docs(rtm): trace the grouped-view contained-card layout (#827)

Refs #827

.gitea/workflows/nightly.yml

@@ -192,17 +192,52 @@ jobs:
           REPO="${{ github.repository }}"
           RUN_URL="${GITEA_URL}/${REPO}/actions/runs/${{ github.run_id }}"
 
+          # --- Gitea API helper ---
+          # api METHOD URL [extra curl args...] — authenticated Gitea API call.
+          # `curl -sf` collapses every HTTP >=400 into a bare "exit 22", which
+          # surfaces as an opaque step failure (issue #839). Instead we read the
+          # status code and, on a >=400 response, print an actionable ::error::
+          # to stderr (so a calling command substitution does not swallow it) and
+          # return 1 — `set -e` then still fails the step. The token is never
+          # echoed (no set -x; never placed in the message).
+          api() {
+            local method="$1" url="$2"; shift 2
+            local resp http
+            resp=$(curl -s -w '\n%{http_code}' -X "$method" \
+              -H "Authorization: token $NIGHTLY_AUDIT_TOKEN" "$@" -- "$url")
+            http=${resp##*$'\n'}
+            printf '%s' "${resp%$'\n'*}"
+            case "$http" in
+              2*|3*) return 0 ;;
+              401|403)
+                echo "::error::Gitea returned HTTP $http for $method ${url%%\?*} — the NIGHTLY_AUDIT_TOKEN secret is missing, expired, or lacks issue read+write scope; recreate the renovate_bot PAT and update the secret." >&2
+                return 1 ;;
+              *)
+                echo "::error::Gitea returned HTTP ${http:-(none)} for $method ${url%%\?*}." >&2
+                return 1 ;;
+            esac
+          }
+
           # --- Self-test (mirrors ci.yml §Assert pattern) ---
-          # Tests the exact jq test() call used in the dedupe step, before any
+          # Runs before any real API call so broken logic fails loudly early:
-          # API call, so a broken matcher fails loudly early rather than silently
+          # (a) the jq title matcher used by the dedupe step — proves the regex
-          # opening duplicate issues. Proves the regex only — create-vs-update
+          #     only; the create-vs-update decision is exercised by the
-          # decision is exercised by the workflow_dispatch AC.
+          #     workflow_dispatch AC;
+          # (b) the api helper's HTTP-status handling, driven by a mocked curl so
+          #     it needs no network — proves a 2xx returns the body and a >=400
+          #     fails with an ::error:: instead of an opaque exit 22.
           echo "{\"title\": \"${MARKER}\"}" \
             | jq -e --arg m "$MARKER" '.title | test($m; "i")' > /dev/null \
             || { echo "FAIL: self-test — jq test() missed tracking issue title"; exit 1; }
           echo '{"title": "fix(deps): update dependency esbuild (CVE-2025-12345)"}' \
             | jq -e --arg m "$MARKER" '.title | test($m; "i") | not' > /dev/null \
             || { echo "FAIL: self-test — jq test() incorrectly matched unrelated title"; exit 1; }
+          ( curl() { printf 'OK\n200'; }; [ "$(api GET selftest)" = "OK" ] ) \
+            || { echo "FAIL: self-test — api helper dropped body on HTTP 200"; exit 1; }
+          ( curl() { printf 'nope\n401'; }
+            if api GET selftest >/dev/null 2>/tmp/api_selftest_err; then exit 1; fi
+            grep -q '::error::' /tmp/api_selftest_err ) \
+            || { echo "FAIL: self-test — api helper did not emit ::error:: on HTTP 401"; exit 1; }
           echo "Self-test passed."
 
           # --- Run audit ---
@@ -237,8 +272,7 @@ jobs:
             # Renovate vuln PRs also carry the "security" label, so >1 open
             # "security" issue WILL occur. Title-match (not just label) ensures
             # we deduplicate only our own tracking issue.
-            OPEN_ISSUES=$(curl -sf \
+            OPEN_ISSUES=$(api GET \
-              -H "Authorization: token $NIGHTLY_AUDIT_TOKEN" \
               "${GITEA_URL}/api/v1/repos/${REPO}/issues?state=open&type=issues&labels=security&limit=50")
 
             MATCHED=$(echo "$OPEN_ISSUES" | jq \
@@ -255,11 +289,10 @@ jobs:
                 --arg run_url "$RUN_URL" \
                 '$existing + "\n\n---\n\nUpdated by run: " + $run_url')
               PAYLOAD=$(jq -n --arg body "$NEW_BODY" '{"body": $body}')
-              curl -sf -X PATCH \
+              api PATCH \
-                -H "Authorization: token $NIGHTLY_AUDIT_TOKEN" \
+                "${GITEA_URL}/api/v1/repos/${REPO}/issues/${ISSUE_NUMBER}" \
                 -H "Content-Type: application/json" \
-                -d "$PAYLOAD" \
+                -d "$PAYLOAD" > /dev/null
-                "${GITEA_URL}/api/v1/repos/${REPO}/issues/${ISSUE_NUMBER}" > /dev/null
               echo "Updated tracking issue #${ISSUE_NUMBER}"
             else
               # Closed prior issue that recurs → new issue (not reopened).
@@ -268,24 +301,21 @@ jobs:
                 --arg title "$MARKER" \
                 --arg body "$ISSUE_BODY" \
                 '{"title": $title, "body": $body}')
-              CREATED=$(curl -sf -X POST \
+              CREATED=$(api POST \
-                -H "Authorization: token $NIGHTLY_AUDIT_TOKEN" \
+                "${GITEA_URL}/api/v1/repos/${REPO}/issues" \
                 -H "Content-Type: application/json" \
-                -d "$PAYLOAD" \
+                -d "$PAYLOAD")
-                "${GITEA_URL}/api/v1/repos/${REPO}/issues")
               NEW_NUMBER=$(echo "$CREATED" | jq -r '.number')
               echo "Opened new tracking issue #${NEW_NUMBER}"
 
               # Labels are ignored on issue create in Gitea — add in a follow-up call.
-              LABEL_IDS=$(curl -sf \
+              LABEL_IDS=$(api GET \
-                -H "Authorization: token $NIGHTLY_AUDIT_TOKEN" \
                 "${GITEA_URL}/api/v1/repos/${REPO}/labels?limit=50" \
                 | jq '[.[] | select(.name == "security" or .name == "devops" or .name == "P1-high") | .id]')
-              curl -sf -X POST \
+              api POST \
-                -H "Authorization: token $NIGHTLY_AUDIT_TOKEN" \
+                "${GITEA_URL}/api/v1/repos/${REPO}/issues/${NEW_NUMBER}/labels" \
                 -H "Content-Type: application/json" \
-                -d "{\"labels\": $LABEL_IDS}" \
+                -d "{\"labels\": $LABEL_IDS}" > /dev/null
-                "${GITEA_URL}/api/v1/repos/${REPO}/issues/${NEW_NUMBER}/labels" > /dev/null
             fi
 
             exit "$AUDIT_EXIT"

.specify/rtm.md

@@ -2,7 +2,7 @@
 
 > Living document. One row per `REQ-NNN` across all in-flight and shipped features. The spec
 > itself lives in the **Gitea issue** (issue-only — there is no committed `spec.md`); this
-> matrix is the part of the spec that *is* committed: it links each requirement to its issue,
+> matrix is the part of the spec that _is_ committed: it links each requirement to its issue,
 > the code that implements it, and the test(s) that prove it — so any requirement traces end
 > to end, and any orphan (a requirement with no test) is visible on `main`.
 
@@ -25,16 +25,16 @@
 ## Matrix
 
 | REQ-ID  | Requirement Summary                                                    | Issue    | Feature                            | Implementation File(s)                            | Test(s)                                                                                                                                                                                                                    | Status  |
-|---|---|---|---|---|---|---|
+| ------- | ---------------------------------------------------------------------- | -------- | ---------------------------------- | ------------------------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------- |
-| REQ-001 | Store avatar at `avatars/{userId}`, overwrite | #example | profile-picture-upload (_example) | `UserService` (planned) | `UserServiceAvatarTest#storesUnderUserKey`, `#replaceLeavesNoOrphan` | Planned |
+| REQ-001 | Store avatar at `avatars/{userId}`, overwrite                          | #example | profile-picture-upload (\_example) | `UserService` (planned)                           | `UserServiceAvatarTest#storesUnderUserKey`, `#replaceLeavesNoOrphan`                                                                                                                                                       | Planned |
-| REQ-002 | Upload self avatar → 200 + avatarUrl | #example | profile-picture-upload (_example) | `UserAvatarController`, `UserService` (planned) | `UserAvatarControllerTest#uploadReturnsAvatarUrl` | Planned |
+| REQ-002 | Upload self avatar → 200 + avatarUrl                                   | #example | profile-picture-upload (\_example) | `UserAvatarController`, `UserService` (planned)   | `UserAvatarControllerTest#uploadReturnsAvatarUrl`                                                                                                                                                                          | Planned |
-| REQ-003 | Delete self avatar → avatarUrl null | #example | profile-picture-upload (_example) | `UserAvatarController` (planned) | `UserAvatarControllerTest#deleteClearsAvatar` | Planned |
+| REQ-003 | Delete self avatar → avatarUrl null                                    | #example | profile-picture-upload (\_example) | `UserAvatarController` (planned)                  | `UserAvatarControllerTest#deleteClearsAvatar`                                                                                                                                                                              | Planned |
-| REQ-004 | No avatar → null + initials placeholder | #example | profile-picture-upload (_example) | `UserProfileView`, avatar component (planned) | `avatar-placeholder.svelte.spec.ts` | Planned |
+| REQ-004 | No avatar → null + initials placeholder                                | #example | profile-picture-upload (\_example) | `UserProfileView`, avatar component (planned)     | `avatar-placeholder.svelte.spec.ts`                                                                                                                                                                                        | Planned |
-| REQ-005 | ADMIN_USER may delete others' avatar | #example | profile-picture-upload (_example) | `UserAvatarController` (planned) | `UserAvatarControllerTest#adminDeletesOthersAvatar` | Planned |
+| REQ-005 | ADMIN_USER may delete others' avatar                                   | #example | profile-picture-upload (\_example) | `UserAvatarController` (planned)                  | `UserAvatarControllerTest#adminDeletesOthersAvatar`                                                                                                                                                                        | Planned |
-| REQ-006 | Unauthenticated → 401, store nothing | #example | profile-picture-upload (_example) | `SecurityConfig`, controller (planned) | `UserAvatarControllerTest#unauthenticatedReturns401` | Planned |
+| REQ-006 | Unauthenticated → 401, store nothing                                   | #example | profile-picture-upload (\_example) | `SecurityConfig`, controller (planned)            | `UserAvatarControllerTest#unauthenticatedReturns401`                                                                                                                                                                       | Planned |
-| REQ-007 | Non-image → 400 UNSUPPORTED_FILE_TYPE | #example | profile-picture-upload (_example) | `UserService` (planned) | `UserAvatarControllerTest#rejectsNonImage` | Planned |
+| REQ-007 | Non-image → 400 UNSUPPORTED_FILE_TYPE                                  | #example | profile-picture-upload (\_example) | `UserService` (planned)                           | `UserAvatarControllerTest#rejectsNonImage`                                                                                                                                                                                 | Planned |
-| REQ-008 | Over 2 MB → 400 AVATAR_TOO_LARGE | #example | profile-picture-upload (_example) | `UserService`, `ErrorCode` (planned) | `UserAvatarControllerTest#rejectsOversize` | Planned |
+| REQ-008 | Over 2 MB → 400 AVATAR_TOO_LARGE                                       | #example | profile-picture-upload (\_example) | `UserService`, `ErrorCode` (planned)              | `UserAvatarControllerTest#rejectsOversize`                                                                                                                                                                                 | Planned |
-| REQ-009 | Non-admin on others → 403 FORBIDDEN | #example | profile-picture-upload (_example) | `UserAvatarController` (planned) | `UserAvatarControllerTest#nonAdminForbiddenOnOthers` | Planned |
+| REQ-009 | Non-admin on others → 403 FORBIDDEN                                    | #example | profile-picture-upload (\_example) | `UserAvatarController` (planned)                  | `UserAvatarControllerTest#nonAdminForbiddenOnOthers`                                                                                                                                                                       | Planned |
 | REQ-001 | Render dated entry via shared `formatDocumentDate` (de/en/es)          | #778     | timeline-date-label                | `frontend/src/lib/timeline/dateLabel.ts`          | `dateLabel.spec.ts` › `renders a DAY date localized in German`, `renders a SEASON date with the German season word`, `delegates a same-year RANGE to formatDocumentDate`                                                   | Done    |
 | REQ-002 | Non-UNKNOWN + non-empty date → shared label, `raw=null`, `getLocale()` | #778     | timeline-date-label                | `frontend/src/lib/timeline/dateLabel.ts`          | `dateLabel.spec.ts` › `renders a DAY date localized in German`, `renders a DAY date localized in English`                                                                                                                  | Done    |
 | REQ-003 | `UNKNOWN` → `null` (no chip)                                           | #778     | timeline-date-label                | `frontend/src/lib/timeline/dateLabel.ts`          | `dateLabel.spec.ts` › `returns null for UNKNOWN precision even with a date`, `returns null for UNKNOWN precision without a date`                                                                                           | Done    |
@@ -43,11 +43,12 @@
 | REQ-006 | `timeline` in coverage `include` (80% branch gate)                     | #778     | timeline-date-label                | `frontend/vite.config.ts`                         | coverage `include` now lists `src/lib/timeline/**`; covered by all `dateLabel.spec.ts` cases                                                                                                                               | Done    |
 
 <!-- Append real features below this line, one row per REQ-NNN, with the real issue number. Keep the header row above. -->
+
 | REQ-001 | family-member Person with birthDate → 1 BIRTH event, precision passed through | #776 | derive-person-life-events | `timeline/TimelineEventService#buildBirthEvents` | `DerivedEventsAssemblyTest#should_emit_one_geburt_for_person_with_birthdate`, `#should_pass_birth_precision_through_unchanged` | Done |
 | REQ-002 | family-member Person with deathDate → 1 DEATH event | #776 | derive-person-life-events | `timeline/TimelineEventService#buildDeathEvents` | `DerivedEventsAssemblyTest#should_emit_one_tod_for_person_with_deathdate`, `#should_emit_one_tod_and_zero_geburt_for_person_with_deathdate_only` | Done |
 | REQ-003 | null birthDate → 0 Geburt events | #776 | derive-person-life-events | `timeline/TimelineEventService#buildBirthEvents` | `DerivedEventsAssemblyTest#should_emit_zero_tod_when_person_has_birthdate_but_no_deathdate`, `#should_emit_one_tod_and_zero_geburt_for_person_with_deathdate_only` | Done |
 | REQ-004 | null deathDate → 0 Tod events; no dates → 0 events | #776 | derive-person-life-events | `timeline/TimelineEventService#buildDeathEvents` | `DerivedEventsAssemblyTest#should_emit_no_events_for_person_with_neither_date` | Done |
-| REQ-005 | SPOUSE_OF edge with fromYear → MARRIAGE event, eventDate={fromYear}-01-01, precision=YEAR | #776 | derive-person-life-events | `timeline/TimelineEventService#buildMarriageEvents` | `DerivedEventsAssemblyTest#should_emit_one_heirat_for_spouse_edge_with_fromYear` | Done |
+| REQ-005 | SPOUSE*OF edge with fromYear → MARRIAGE event, eventDate={fromYear}-01-01, precision=YEAR | #776 | derive-person-life-events | `timeline/TimelineEventService#buildMarriageEvents` | `DerivedEventsAssemblyTest#should_emit_one_heirat_for_spouse_edge_with_fromYear` | Done |
 | REQ-006 | SPOUSE_OF edge with null fromYear → MARRIAGE emitted, eventDate=null, precision=UNKNOWN | #776 | derive-person-life-events | `timeline/TimelineEventService#buildMarriageEvents` | `DerivedEventsAssemblyTest#should_emit_unknown_precision_heirat_when_fromYear_is_null` | Done |
 | REQ-007 | exactly one MARRIAGE per SPOUSE_OF row (dedup on relationship id) | #776 | derive-person-life-events | `timeline/TimelineEventService#buildMarriageEvents` | `DerivedEventsAssemblyTest#should_emit_exactly_one_heirat_when_both_spouses_in_scope`, `#should_emit_two_heirat_for_person_married_to_two_partners` | Done |
 | REQ-008 | synthetic prefixed ids (birth:/death:/marriage:), never parseable as UUID | #776 | derive-person-life-events | `timeline/TimelineEventService#buildBirthEvents,#buildDeathEvents,#buildMarriageEvents` | `DerivedEventsAssemblyTest#should_mint_prefixed_synthetic_ids_never_uuid` | Done |
@@ -139,6 +140,25 @@
 | REQ-014 | no change to DTO order, density threshold (12), gap-folding, or ol/section/h2 structure | #833 | zeitstrahl-visual-fidelity | `frontend/src/lib/timeline/*` | existing timeline + `zeitstrahl/page.server.test.ts` suites stay green (142 tests) | Done |
 | REQ-015 | new user-facing strings are Paraglide keys present in de/en/es with matching key sets | #833 | zeitstrahl-visual-fidelity | `frontend/messages/{de,en,es}.json` | `messages.spec.ts#zeitstrahl visual-fidelity keys are present in all locales`, `#identical key sets` | Done |
 | REQ-016 | LetterCard with no title → no ✉, no sr-only "Brief"; sender→receiver + date still render | #833 | zeitstrahl-visual-fidelity | `frontend/src/lib/timeline/LetterCard.svelte` | `LetterCard.svelte.spec.ts#renders no ✉ glyph and no "Brief" label when the title is empty` | Done |
+| REQ-001 | store relationship from/to as nullable LocalDate + NOT-NULL DatePrecision (default UNKNOWN) | #837 | relationship-edit-dates | `person/relationship/PersonRelationship.java`, `V78__relationship_years_to_localdate.sql` | `RelationshipMigrationTest#yearColumnsDropped_andNamedCheckConstraintsExist`, `RelationshipServiceTest#addRelationship_persists_with_storage_truth` | Done |
+| REQ-002 | V78 backfills non-null years as `{year}-01-01`/YEAR, nulls → null/UNKNOWN, rows preserved | #837 | relationship-edit-dates | `V78__relationship_years_to_localdate.sql` | `RelationshipMigrationTest#backfill_fromYearAndToYear_becomeYearPrecisionDates`, `#backfill_bothNull_leavesDatesNullAndPrecisionsUnknown`, `#backfill_preservesRowCount` | Done |
+| REQ-003 | named DB CHECKs: coherence both ends + fromDate ≤ toDate | #837 | relationship-edit-dates | `V78__relationship_years_to_localdate.sql` | `RelationshipMigrationTest#orderCheckConstraint_rejectsToDateBeforeFromDate`, `#coherenceCheckConstraint_rejectsDatePresentWithUnknownPrecision` | Done |
+| REQ-004 | PUT updates the relationship → 200 RelationshipDTO | #837 | relationship-edit-dates | `person/relationship/RelationshipController#updateRelationship`, `RelationshipService#updateRelationship` | `RelationshipControllerTest#updateRelationship_returns200_with_RelationshipDTO_for_WRITE_ALL_user`, `RelationshipServiceIntegrationTest#updateRelationship_persists_new_type_dates_and_notes`, `page.server.spec.ts#updateRelationship PUTs to the relId path with the new body` | Done |
+| REQ-005 | create + update rejected with 403 without WRITE_ALL | #837 | relationship-edit-dates | `person/relationship/RelationshipController` (`@RequirePermission`) | `RelationshipControllerTest#updateRelationship_returns403_for_READ_ALL_only_user`, `#addRelationship_returns403_for_user_with_READ_ALL_only` | Done |
+| REQ-006 | relId not existing / not owned by person → 404 RELATIONSHIP_NOT_FOUND | #837 | relationship-edit-dates | `person/relationship/RelationshipService#loadOwnedRelationship` | `RelationshipServiceTest#updateRelationship_throws_NOT_FOUND_when_rel_belongs_to_different_person`, `RelationshipServiceIntegrationTest#updateRelationship_throws_404_when_rel_belongs_to_different_person` | Done |
+| REQ-007 | update with relatedPersonId == {id} → 400 VALIDATION_ERROR | #837 | relationship-edit-dates | `person/relationship/RelationshipService#updateRelationship` | `RelationshipServiceTest#updateRelationship_throws_VALIDATION_ERROR_on_self_relation` | Done |
+| REQ-008 | resulting (person, relatedPerson, type) duplicate → 409 DUPLICATE_RELATIONSHIP | #837 | relationship-edit-dates | `person/relationship/RelationshipService#updateRelationship` | `RelationshipServiceTest#updateRelationship_throws_DUPLICATE_when_db_constraint_violated` | Done |
+| REQ-009 | update to PARENT_OF with reverse PARENT_OF present → 409 CIRCULAR_RELATIONSHIP | #837 | relationship-edit-dates | `person/relationship/RelationshipService#updateRelationship` | `RelationshipServiceTest#updateRelationship_throws_CIRCULAR_when_reverse_PARENT_OF_exists` | Done |
+| REQ-010 | toDate before fromDate → 400 INVALID_RELATIONSHIP_DATES | #837 | relationship-edit-dates | `person/relationship/RelationshipService#validateRelationshipDates`, `exception/ErrorCode`, `frontend/src/lib/shared/errors.ts` | `RelationshipServiceTest#addRelationship_throws_INVALID_RELATIONSHIP_DATES_when_toDate_before_fromDate`, `#updateRelationship_throws_INVALID_RELATIONSHIP_DATES_when_toDate_before_fromDate` | Done |
+| REQ-011 | date+UNKNOWN precision, or precision without date → 400 INVALID_DATE_PRECISION | #837 | relationship-edit-dates | `person/relationship/RelationshipService#requireDatePrecisionCoherence` | `RelationshipServiceTest#addRelationship_throws_INVALID_DATE_PRECISION_when_date_present_but_precision_unknown`, `#addRelationship_throws_INVALID_DATE_PRECISION_when_precision_set_without_date` | Done |
+| REQ-012 | invalid enum / missing relatedPersonId·relationType / notes > 2000 → 400 VALIDATION_ERROR | #837 | relationship-edit-dates | `person/relationship/RelationshipUpsertRequest` (Bean Validation), `RelationshipController` | `RelationshipControllerTest#updateRelationship_returns400_when_relationType_is_unknown_value`, `#addRelationship_returns400_when_relationType_is_unknown_value` | Done |
+| REQ-013 | updating into a family type flags both endpoints (additive) | #837 | relationship-edit-dates | `person/relationship/RelationshipService#updateRelationship` | `RelationshipServiceTest#updateRelationship_marks_both_endpoints_family_when_updated_to_family_type` | Done |
+| REQ-014 | persist + display notes on create, update, read and edit views | #837 | relationship-edit-dates | `person/relationship/RelationshipService`, `frontend/.../AddRelationshipForm.svelte`, `routes/persons/[id]/PersonRelationshipsCard.svelte` | `RelationshipServiceIntegrationTest#updateRelationship_persists_new_type_dates_and_notes`, `AddRelationshipForm.svelte.spec.ts#round-trips the notes into the textarea`, `PersonRelationshipsCard.svelte.test.ts#shows the notes line` | Done |
+| REQ-015 | detail view shows the date range at its precision; no dates → no date line | #837 | relationship-edit-dates | `frontend/src/lib/person/relationshipDates.ts`, `routes/persons/[id]/PersonRelationshipsCard.svelte` | `relationshipDates.spec.ts`, `PersonRelationshipsCard.svelte.test.ts#renders the date range at its stored precision`, `#renders no date line when the relationship has no dates` | Done |
+| REQ-016 | edit affordance opens a form pre-filled with type/person/dates+precision/notes; precision DAY/MONTH/YEAR | #837 | relationship-edit-dates | `frontend/.../AddRelationshipForm.svelte`, `RelationshipDateField.svelte`, `RelationshipChip.svelte` | `AddRelationshipForm.svelte.spec.ts#pre-fills the from-date as dd.mm.yyyy`, `#offers only DAY/MONTH/YEAR in each precision select`, `RelationshipChip.svelte.spec.ts#shows an Edit affordance with an accessible name when canWrite and onEdit` | Done |
+| REQ-017 | derived Heirat sources SPOUSE_OF.fromDate + fromDatePrecision | #837 | relationship-edit-dates | `timeline/TimelineEventService#buildMarriageEvents` | `DerivedEventsAssemblyTest#should_emit_day_precision_heirat_from_spouse_fromDate` | Done |
+| REQ-018 | unauthenticated PUT → 401, no row modified | #837 | relationship-edit-dates | `person/relationship/RelationshipController` (SecurityConfig) | `RelationshipControllerTest#updateRelationship_returns401_whenUnauthenticated_and_does_not_touch_service` | Done |
+| REQ-019 | while a create/update request is in flight, submit is disabled + shows a progress indicator | #837 | relationship-edit-dates | `frontend/src/lib/person/relationship/AddRelationshipForm.svelte` | `AddRelationshipForm.svelte.spec.ts#disables the submit and shows a progress spinner while a submit is in flight` | Done |
 | REQ-001 | TimelineEntryDTO carries rootTagId/rootTagName/rootTagColor for LETTER entries, assembled in-transaction (id+name+token only) | #835 | zeitstrahl-tag-chips | `timeline/TimelineEntryDTO`, `timeline/TimelineService#mapDocument` | `TimelineServiceTest#letter_with_tags_carries_its_primary_root_tag` | Done |
 | REQ-002 | the three root-tag fields are nullable and not `@Schema(requiredMode = REQUIRED)` | #835 | zeitstrahl-tag-chips | `timeline/TimelineEntryDTO`, `frontend/src/lib/generated/api.ts` (optional) | `TimelineServiceTest#untagged_letter_has_no_root_tag_fields` (+ regenerated `api.ts` shows `rootTag*?`) | Done |
 | REQ-003 | primary tag = root ancestor of the alphabetically-first assigned tag, resolved via TagService | #835 | zeitstrahl-tag-chips | `tag/TagService#resolveRootTags`, `timeline/TimelineService#primaryTag` | `TimelineServiceTest#letter_with_tags_carries_its_primary_root_tag`, `TagServiceTest#resolveRootTags_walksChildToRoot_withRootColor`, `TagServiceIntegrationTest#resolveRootTags_walksPersistedChainToRoot_withRootColor` | Done |
@@ -154,3 +174,45 @@
 | REQ-012 | chip renders wherever a LetterCard renders (global timeline + expanded YearLetterStrip) | #835 | zeitstrahl-tag-chips | `frontend/src/lib/timeline/LetterCard.svelte` | `LetterCard.svelte.spec.ts#renders the chip inside an expanded YearLetterStrip too` | Done |
 | REQ-013 | sr-only theme label is a Paraglide key present in de/en/es | #835 | zeitstrahl-tag-chips | `frontend/messages/{de,en,es}.json` | `messages.spec.ts#zeitstrahl tag-chip label key is present in all locales` | Done |
 | REQ-014 | GET /api/timeline stays read-only (READ_ALL); no new endpoint/ErrorCode/IDOR; assembly logs UUIDs only | #835 | zeitstrahl-tag-chips | `timeline/TimelineController` (unchanged), `timeline/TimelineService` | `TimelineControllerTest#returns_200_with_read_all_permission`, `#returns_403_when_authenticated_without_read_all` (unchanged path); no tag names logged (review) | Done |
+| REQ-001 | TimelineFilters is presentation-only (3 $bindable layer booleans + onChange); no goto/url.searchParams/api.GET/fetch | #780 | timeline-layer-filter | `frontend/src/lib/timeline/TimelineFilters.svelte` | `TimelineFilters.svelte.spec.ts#renders the three layer toggles with accessible names`, `#reflects a layer as pressed and flips it, firing onChange`; `timelineFilterBoundary.spec.ts` | Done |
+| REQ-002 | route derives a client-side $derived filtered view, passes it to TimelineView; no goto/fetch on toggle | #780 | timeline-layer-filter | `frontend/src/routes/zeitstrahl/+page.svelte`, `frontend/src/lib/timeline/timelineFilter.ts#filterTimeline` | `page.svelte.spec.ts#hides letter cards when the Letters layer is off ... with no fetch`; `timelineFilterBoundary.spec.ts` | Done |
+| REQ-003 | Personal off → personal events (curated + derived life-events) hidden client-side | #780 | timeline-layer-filter | `frontend/src/lib/timeline/timelineFilter.ts#filterTimeline` | `timelineFilter.spec.ts#hides personal events — curated and derived`, `page.svelte.spec.ts#hides personal event cards` | Done |
+| REQ-004 | Historical off → historical event entries hidden client-side | #780 | timeline-layer-filter | `frontend/src/lib/timeline/timelineFilter.ts#filterTimeline` | `timelineFilter.spec.ts#hides HISTORICAL events`, `page.svelte.spec.ts#hides historical event cards` | Done |
+| REQ-005 | Letters off → letter entries hidden client-side | #780 | timeline-layer-filter | `frontend/src/lib/timeline/timelineFilter.ts#filterTimeline` | `timelineFilter.spec.ts#hides LETTER entries`, `page.svelte.spec.ts#hides letter cards` | Done |
+| REQ-006 | zero visible → filter empty-state + one-click reset below the open bar (never blank, never generic empty) | #780 | timeline-layer-filter | `frontend/src/routes/zeitstrahl/+page.svelte`, `frontend/src/lib/timeline/timelineFilter.ts#filterTimeline` | `page.svelte.spec.ts#shows the filtered-empty message + reset below the open bar`, `timelineFilter.spec.ts#drops year bands that become empty` | Done |
+| REQ-007 | sticky "Filter (N aktiv)" trigger; N from isDefaultState/hiddenLayerCount; 44px target | #780 | timeline-layer-filter | `frontend/src/lib/timeline/timelineFilter.ts`, `frontend/src/lib/timeline/TimelineFilters.svelte` | `timelineFilter.spec.ts#isDefaultState`, `#hiddenLayerCount`; `TimelineFilters.svelte.spec.ts#shows a plain trigger ... and a count`, `#gives the trigger a 44px touch target` | Done |
+| REQ-008 | reset text button restores all layers on; visibility tracks a $derived any-layer-off flag | #780 | timeline-layer-filter | `frontend/src/lib/timeline/TimelineFilters.svelte` | `TimelineFilters.svelte.spec.ts#hides the reset button by default and restores all layers when activated` | Done |
+| REQ-009 | prefers-reduced-motion → slide duration 0 (matchMedia guard reused from documents/[id]/+page.svelte:57) | #780 | timeline-layer-filter | `frontend/src/lib/timeline/TimelineFilters.svelte` | manual reduced-motion check + svelte-autofixer/code review (guard reused, only the slide `duration` zeroed) | Done |
+| REQ-010 | 8 timeline_filter*_ keys in de/en/es; trigger vs trigger*active({count}) distinct | #780 | timeline-layer-filter | `frontend/messages/{de,en,es}.json` | `messages.spec.ts#zeitstrahl layer-filter keys are present in all locales (#780 REQ-010)` | Done |
+| REQ-001 | WRITE_ALL viewer → "Ereignis hinzufügen" link to /zeitstrahl/events/new in the wrapping Zeitstrahl header | #842 | timeline-curator-affordances | `frontend/src/routes/zeitstrahl/+page.svelte`, `frontend/messages/{de,en,es}.json` | `zeitstrahl/page.svelte.spec.ts#renders the add-event CTA in a wrapping header when the viewer can write` | Done |
+| REQ-002 | viewer without WRITE_ALL → no add-event affordance on /zeitstrahl | #842 | timeline-curator-affordances | `frontend/src/routes/zeitstrahl/+page.svelte` | `zeitstrahl/page.svelte.spec.ts#renders no add-event CTA when the viewer cannot write` | Done |
+| REQ-003 | WRITE_ALL viewer → person-page "Ereignis für diese Person" link to /zeitstrahl/events/new?personId={id} | #842 | timeline-curator-affordances | `frontend/src/routes/persons/[id]/PersonCard.svelte`, `frontend/messages/{de,en,es}.json` | `PersonCard.svelte.spec.ts#shows an add-event link pre-seeded with the person to a curator` | Done |
+| REQ-004 | viewer without WRITE_ALL → no add-event affordance on /persons/{id} | #842 | timeline-curator-affordances | `frontend/src/routes/persons/[id]/PersonCard.svelte` | `PersonCard.svelte.spec.ts#renders no add-event link to a reader` | Done |
+| REQ-005 | WRITE_ALL → EventPill edit link /zeitstrahl/events/{eventId}/edit for a curated PERSONAL event | #842 | timeline-curator-affordances | `frontend/src/lib/timeline/EventPill.svelte` | `EventPill.svelte.spec.ts#shows an edit affordance for a curated PERSONAL event when canWrite is true` | Done |
+| REQ-006 | WRITE_ALL → WorldBand edit link /zeitstrahl/events/{eventId}/edit for a curated HISTORICAL event (new inline ✎) | #842 | timeline-curator-affordances | `frontend/src/lib/timeline/WorldBand.svelte` | `WorldBand.svelte.spec.ts#shows an edit affordance for a curated HISTORICAL event when canWrite is true`, `#mirrors the EventPill pencil` | Done |
+| REQ-007 | viewer without WRITE_ALL → neither EventPill nor WorldBand renders an edit link | #842 | timeline-curator-affordances | `frontend/src/lib/timeline/EventPill.svelte`, `frontend/src/lib/timeline/WorldBand.svelte` | `EventPill.svelte.spec.ts#renders no edit affordance for a curated PERSONAL event when canWrite is false`, `WorldBand.svelte.spec.ts#renders no edit affordance for a curated HISTORICAL event when canWrite is false`, `TimelineView.svelte.spec.ts#renders no edit links in either path when canWrite is false` | Done |
+| REQ-008 | derived OR null eventId → no edit link regardless of permission (contract preserved) | #842 | timeline-curator-affordances | `frontend/src/lib/timeline/EventPill.svelte`, `frontend/src/lib/timeline/WorldBand.svelte` | `EventPill.svelte.spec.ts#shows no edit affordance when eventId is null even with canWrite`, `#shows no edit affordance for a derived event even with canWrite`, `WorldBand.svelte.spec.ts#shows no edit affordance when eventId is null even with canWrite` | Done |
+| REQ-009 | TimelineView threads canWrite through the year-band path and the undated bucket (identical gate) | #842 | timeline-curator-affordances | `frontend/src/lib/timeline/TimelineView.svelte`, `frontend/src/lib/timeline/YearBand.svelte` | `TimelineView.svelte.spec.ts#threads canWrite to a curated event in both a year band and the undated bucket`, `#threads canWrite to a curated HISTORICAL world band in both paths` | Done |
+| REQ-010 | person add-event opens #781 create form prefilled with the person, returns to /persons/{id} on save | #842 | timeline-curator-affordances | `frontend/src/routes/persons/[id]/PersonCard.svelte`, `frontend/src/routes/zeitstrahl/events/new/+page.server.ts` (#781) | `PersonCard.svelte.spec.ts#shows an add-event link pre-seeded with the person to a curator` (URL), `zeitstrahl/events/new/page.server.spec.ts#redirects to /persons/{id} when originPersonId is a valid UUID` (#781) | Done |
+| REQ-011 | non-curator direct nav to /zeitstrahl/events/new or /{id}/edit → 403 (existing #781 route guard, regression) | #842 | timeline-curator-affordances | `frontend/src/routes/zeitstrahl/events/new/+page.server.ts`, `frontend/src/routes/zeitstrahl/events/[id]/edit/+page.server.ts` (#781, unchanged — both share `requireWriteAll`) | `zeitstrahl/events/new/page.server.spec.ts#throws 403 for an authenticated user without WRITE_ALL`, `zeitstrahl/events/[id]/edit/page.server.spec.ts#throws 403 for a user without WRITE_ALL` | Done |
+| REQ-001 | axis-fixed layers (life-events, pills, world-bands) render identically across all 3 modes; only loose letters re-bundle | #827 | timeline-grouping-modes | `frontend/src/lib/timeline/TimelineView.svelte`, `frontend/src/lib/timeline/YearBand.svelte` | `grouping-event-layer-identity.svelte.spec.ts#renders the event pills and world-bands identically across all three grouping modes`, `YearBand.svelte.spec.ts#still renders the event world-band in Ereignis mode` | Done |
+| REQ-002 | mode switch re-bundles loose letters over the layer-filtered view, no GET /api/timeline refetch | #827 | timeline-grouping-modes | `frontend/src/routes/zeitstrahl/+page.svelte`, `frontend/src/lib/timeline/timelineGrouping.ts`, `frontend/src/lib/timeline/TimelineView.svelte` | `zeitstrahl/page.svelte.spec.ts#regroups loose letters under their event client-side`, `e2e/zeitstrahl-grouping.spec.ts#switching grouping modes issues no extra timeline fetch` | Done |
+| REQ-003 | Ereignis clusters each loose letter under the curated event whose documents contain it | #827 | timeline-grouping-modes | `frontend/src/lib/timeline/timelineGrouping.ts#bucketLetters`, `frontend/src/lib/timeline/YearBand.svelte`, `frontend/src/lib/timeline/LetterBucket.svelte` | `timelineGrouping.spec.ts#clusters letters under the curated event named by linkedEventId`, `YearBand.svelte.spec.ts#clusters loose letters under their linked event in Ereignis mode` | Done |
+| REQ-004 | Thema buckets each loose letter per year under its primary root tag (rootTagId) | #827 | timeline-grouping-modes | `frontend/src/lib/timeline/timelineGrouping.ts#bucketLetters`, `frontend/src/lib/timeline/YearBand.svelte`, `frontend/src/lib/timeline/LetterBucket.svelte` | `timelineGrouping.spec.ts#buckets letters under their primary root tag with name and colour`, `YearBand.svelte.spec.ts#buckets loose letters under their root tag in Thema mode` | Done |
+| REQ-005 | TimelineEntryDTO carries nullable linkedEventId, resolved in one batched membership pass | #827 | timeline-grouping-modes | `backend/.../timeline/TimelineEntryDTO.java`, `backend/.../timeline/TimelineService.java#resolveLetterEventLinks`, `frontend/src/lib/generated/api.ts` | `TimelineServiceTest#letter_in_a_curated_events_documents_carries_that_events_id` | Done |
+| REQ-005b | linkedEventId is nullable / not @Schema REQUIRED; null for non-letter entries | #827 | timeline-grouping-modes | `backend/.../timeline/TimelineEntryDTO.java`, `frontend/src/lib/generated/api.ts` (`linkedEventId?`) | `TimelineServiceTest#letter_in_no_curated_event_has_null_linkedEventId` | Done |
+| REQ-006 | Ereignis: letter with null linkedEventId → per-year "Weitere Briefe" bucket | #827 | timeline-grouping-modes | `frontend/src/lib/timeline/timelineGrouping.ts`, `frontend/src/lib/timeline/LetterBucket.svelte` | `timelineGrouping.spec.ts#drops a letter with no linkedEventId into the fallback bucket`, `LetterBucket.svelte.spec.ts#uses the localized "Weitere Briefe" label` | Done |
+| REQ-007 | Thema: untagged letter → per-year "Ohne Thema" bucket | #827 | timeline-grouping-modes | `frontend/src/lib/timeline/timelineGrouping.ts`, `frontend/src/lib/timeline/LetterBucket.svelte` | `timelineGrouping.spec.ts#drops an untagged letter into the "Ohne Thema" fallback bucket`, `LetterBucket.svelte.spec.ts#uses the localized "Ohne Thema" label` | Done |
+| REQ-008 | multi-tagged letter appears under exactly one root tag, never duplicated | #827 | timeline-grouping-modes | `frontend/src/lib/timeline/timelineGrouping.ts` | `timelineGrouping.spec.ts#places a letter in exactly one bucket` | Done |
+| REQ-009 | tag names + hint render via `{...}` escaping; grep gate forbids `{@html}` in lib/timeline | #827 | timeline-grouping-modes | `frontend/src/lib/timeline/BucketHeaderChip.svelte`, `frontend/src/lib/timeline/LetterCard.svelte`, `frontend/src/lib/timeline/TagChip.svelte` | `BucketHeaderChip.svelte.spec.ts#renders an HTML-bearing name as inert text`, `timeline-no-raw-html.spec.ts#no timeline component contains the raw-HTML directive` | Done |
+| REQ-010 | grouping control is a keyboard-navigable role=radiogroup, ≥44px text segments, default Datum, dark-mode contrast | #827 | timeline-grouping-modes | `frontend/src/lib/timeline/GroupingControl.svelte` | `GroupingControl.svelte.spec.ts#renders three radios inside a radiogroup`, `#moves the selection forward with the right arrow key`, `#each segment has a tap target of at least 44×44px`, `#defaults to Datum`; `e2e/zeitstrahl-grouping.spec.ts#no wcag2a/wcag2aa violations ... (light + dark)` | Done |
+| REQ-011 | ≤320px: control overflow-free + tap ≥44px, each abbreviation carries its full word as aria-label | #827 | timeline-grouping-modes | `frontend/src/lib/timeline/GroupingControl.svelte` | `GroupingControl.svelte.spec.ts#exposes each segment full word as an aria-label`, `e2e/zeitstrahl-grouping.spec.ts#the control stays overflow-free and operable at 320px` | Done |
+| REQ-012 | new grouping/bucket Paraglide keys in de/en/es; no collision with existing timeline*_ keys | #827 | timeline-grouping-modes | `frontend/messages/{de,en,es}.json` | `messages.spec.ts#zeitstrahl grouping + bucket keys are present in all locales (#827 REQ-012)`, `messages.spec.ts#de, en, and es have identical key sets` | Done |
+| REQ-013 | failed timeline fetch → existing localized error via getErrorMessage; grouping has no independent failure mode | #827 | timeline-grouping-modes | `frontend/src/routes/zeitstrahl/+page.server.ts` (#779, unchanged) | `zeitstrahl/page.server` error path (#779 — getErrorMessage(extractErrorCode)) | Done |
+| REQ-014 | Ereignis event-clustered letters live inside a **contained card whose header is the same-year curated event** (glyph, title, date, provenance, edit pencil) — the title reads once, no separate floating pill; letters render as the compact `.lcard.ev` variant, first 5 + show-more (redesign #847 → #827 grouped-card layout) | #827 | timeline-grouping-modes | `frontend/src/lib/timeline/LetterCard.svelte`, `frontend/src/lib/timeline/LetterBucket.svelte`, `frontend/src/lib/timeline/YearBand.svelte` | `LetterCard.svelte.spec.ts#carries the .lcard.ev class in the event variant`, `LetterBucket.svelte.spec.ts#renders the curated event as the card header when given an `event` (no separate pill)`, `LetterBucket.svelte.spec.ts#shows no edit affordance in the header when canWrite is false`, `YearBand.svelte.spec.ts#renders a same-year curated event as one card header, with no separate pill and no duplicate title` | Done |
+| REQ-015 | Thema bucket-header chip tinted via rootTagColor `var(--c-tag-*)`, neutral fallback when null/unknown; **label kept in a fixed ink for ≥4.5:1 contrast** (redesign #847) | #827 | timeline-grouping-modes | `frontend/src/lib/timeline/BucketHeaderChip.svelte` | `BucketHeaderChip.svelte.spec.ts#tints the chip with var(--c-tag-{token})`, `#renders a neutral chip with no --c-tag- binding when colour is null`, `#falls back to neutral for an unknown colour token`, `#paints the label in a fixed ink colour, never the saturated tag token` | Done |
+| REQ-016 | header meta-line grouping segment tracks the active mode (date/event/thema keys) | #827 | timeline-grouping-modes | `frontend/src/routes/zeitstrahl/+page.svelte` | `zeitstrahl/page.svelte.spec.ts#updates the meta-line grouping label when a mode is chosen` | Done |
+| REQ-017 | Thema: per-letter TagChip suppressed inside its own bucket; still shown in Datum/Ereignis | #827 | timeline-grouping-modes | `frontend/src/lib/timeline/LetterCard.svelte`, `frontend/src/lib/timeline/LetterBucket.svelte` | `LetterCard.svelte.spec.ts#suppresses the per-letter tag chip when asked`, `#still shows the per-letter tag chip when not suppressed`, `LetterBucket.svelte.spec.ts#suppresses the per-letter tag chip inside its own root-tag bucket` | Done |
+| REQ-018 | Letters layer off → grouping control disabled (kept in place), mode retained | #827 | timeline-grouping-modes | `frontend/src/routes/zeitstrahl/+page.svelte`, `frontend/src/lib/timeline/GroupingControl.svelte`, `frontend/src/lib/timeline/timelineGrouping.ts#hasLooseLetters` | `zeitstrahl/page.svelte.spec.ts#disables the grouping control when the Letters layer is off`, `GroupingControl.svelte.spec.ts#retains the active mode while disabled`, `timelineGrouping.spec.ts#hasLooseLetters` | Done |
+| REQ-019 | Ereignis: letter whose only linking event was filtered off → "Weitere Briefe" (never re-introduced) | #827 | timeline-grouping-modes | `frontend/src/lib/timeline/timelineGrouping.ts#buildEventLookup`, `frontend/src/lib/timeline/TimelineView.svelte` | `timelineGrouping.spec.ts#drops a letter whose linked event is absent from the lookup into fallback` | Done |
+| REQ-020 | Grouped clusters are **contained colour-railed cards** (bordered, rounded, surface) carrying compact cards; a cluster shows the first `CLUSTER_PREVIEW` (5) letters behind a show-more toggle, and the leftover bin is a **collapsed count-only drawer** revealed on demand — the month-density `YearLetterStrip` is no longer used in grouped mode (still used in Datum dense years) (redesign #847 → #827 grouped-card layout) | #827 | timeline-grouping-modes | `frontend/src/lib/timeline/LetterBucket.svelte`, `frontend/src/lib/timeline/timelineGrouping.ts#CLUSTER_PREVIEW`, `frontend/src/lib/timeline/LetterCard.svelte` | `LetterBucket.svelte.spec.ts#renders the cluster as a contained card (bordered, rounded, surface)`, `#binds a tag bucket together with a coloured left rail from its token`, `#shows only the first 5 letters with a show-more toggle when the cluster is larger`, `#expands to all letters and collapses back on toggle`, `#renders collapsed — count + reveal, no letter cards — until opened`, `#reveals the first 5 letters when opened`, `LetterCard.svelte.spec.ts#renders the compact variant on a single tighter row` | Done |

CLAUDE.md

@@ -170,7 +170,7 @@ Input DTOs live flat in the domain package. Response types are the model entitie
 
 → See [CONTRIBUTING.md §Error handling](./CONTRIBUTING.md#error-handling)
 
-**LLM reminder:** use `DomainException.notFound/forbidden/conflict/internal()` from service methods — never throw raw exceptions. When adding a new `ErrorCode`: (1) add to `ErrorCode.java`, (2) add to `ErrorCode` type in `frontend/src/lib/shared/errors.ts`, (3) add a `case` in `getErrorMessage()`, (4) add i18n keys in `messages/{de,en,es}.json`. Valid error codes include: `TOO_MANY_LOGIN_ATTEMPTS` (returned by `LoginRateLimiter` as HTTP 429 when a brute-force threshold is exceeded); `JOURNEY_NOTE_TOO_LONG`, `JOURNEY_DOCUMENT_ALREADY_ADDED`, `GESCHICHTE_TYPE_IMMUTABLE`, `GESCHICHTE_TITLE_TOO_LONG`, `GESCHICHTE_INTRO_TOO_LONG` (journey/geschichte domain constraints); `TIMELINE_EVENT_NOT_FOUND`, `TIMELINE_EVENT_CONFLICT`, `TIMELINE_TITLE_TOO_LONG` (timeline event CRUD), plus a generic `CONFLICT` (409 optimistic-lock backstop).
+**LLM reminder:** use `DomainException.notFound/forbidden/conflict/internal()` from service methods — never throw raw exceptions. When adding a new `ErrorCode`: (1) add to `ErrorCode.java`, (2) add to `ErrorCode` type in `frontend/src/lib/shared/errors.ts`, (3) add a `case` in `getErrorMessage()`, (4) add i18n keys in `messages/{de,en,es}.json`. Valid error codes include: `TOO_MANY_LOGIN_ATTEMPTS` (returned by `LoginRateLimiter` as HTTP 429 when a brute-force threshold is exceeded); `JOURNEY_NOTE_TOO_LONG`, `JOURNEY_DOCUMENT_ALREADY_ADDED`, `GESCHICHTE_TYPE_IMMUTABLE`, `GESCHICHTE_TITLE_TOO_LONG`, `GESCHICHTE_INTRO_TOO_LONG` (journey/geschichte domain constraints); `TIMELINE_EVENT_NOT_FOUND`, `TIMELINE_EVENT_CONFLICT`, `TIMELINE_TITLE_TOO_LONG` (timeline event CRUD); `INVALID_RELATIONSHIP_DATES` (relationship `toDate` before `fromDate`), plus a generic `CONFLICT` (409 optimistic-lock backstop).
 
 ### Security / Permissions
 
@@ -280,7 +280,7 @@ Back button pattern — use the shared `<BackButton>` component from `$lib/share
 
 → See [CONTRIBUTING.md §Error handling](./CONTRIBUTING.md#error-handling)
 
-**LLM reminder:** when adding a new `ErrorCode`: (1) add to `ErrorCode.java`, (2) add to `ErrorCode` type in `frontend/src/lib/shared/errors.ts`, (3) add a `case` in `getErrorMessage()`, (4) add i18n keys in `messages/{de,en,es}.json`. Valid error codes include: `TOO_MANY_LOGIN_ATTEMPTS` (returned by `LoginRateLimiter` as HTTP 429 when a brute-force threshold is exceeded); `JOURNEY_NOTE_TOO_LONG`, `JOURNEY_DOCUMENT_ALREADY_ADDED`, `GESCHICHTE_TYPE_IMMUTABLE`, `GESCHICHTE_TITLE_TOO_LONG`, `GESCHICHTE_INTRO_TOO_LONG` (journey/geschichte domain constraints); `TIMELINE_EVENT_NOT_FOUND`, `TIMELINE_EVENT_CONFLICT`, `TIMELINE_TITLE_TOO_LONG` (timeline event CRUD), plus a generic `CONFLICT` (409 optimistic-lock backstop).
+**LLM reminder:** when adding a new `ErrorCode`: (1) add to `ErrorCode.java`, (2) add to `ErrorCode` type in `frontend/src/lib/shared/errors.ts`, (3) add a `case` in `getErrorMessage()`, (4) add i18n keys in `messages/{de,en,es}.json`. Valid error codes include: `TOO_MANY_LOGIN_ATTEMPTS` (returned by `LoginRateLimiter` as HTTP 429 when a brute-force threshold is exceeded); `JOURNEY_NOTE_TOO_LONG`, `JOURNEY_DOCUMENT_ALREADY_ADDED`, `GESCHICHTE_TYPE_IMMUTABLE`, `GESCHICHTE_TITLE_TOO_LONG`, `GESCHICHTE_INTRO_TOO_LONG` (journey/geschichte domain constraints); `TIMELINE_EVENT_NOT_FOUND`, `TIMELINE_EVENT_CONFLICT`, `TIMELINE_TITLE_TOO_LONG` (timeline event CRUD); `INVALID_RELATIONSHIP_DATES` (relationship `toDate` before `fromDate`), plus a generic `CONFLICT` (409 optimistic-lock backstop).
 
 ---
 

backend/src/main/java/org/raddatz/familienarchiv/document/DatePrecisionValidation.java

@@ -0,0 +1,42 @@
+package org.raddatz.familienarchiv.document;
+
+import org.raddatz.familienarchiv.exception.DomainException;
+import org.raddatz.familienarchiv.exception.ErrorCode;
+
+import java.time.LocalDate;
+
+/**
+ * Cross-field validation and normalization shared by every domain that stores a
+ * {@link LocalDate} + {@link DatePrecision} pair — a person's life dates (ADR-039 / V76)
+ * and a relationship's from/to dates (ADR-044 / V78). Kept out of {@link DatePrecision}
+ * itself because that enum is a frozen contract mirror of the import normalizer (ADR-025)
+ * and must carry no behaviour.
+ */
+public final class DatePrecisionValidation {
+
+    private DatePrecisionValidation() {}
+
+    /**
+     * Enforces the date ⇔ precision coherence the V76/V78 CHECK constraints also enforce:
+     * a date requires a non-{@code UNKNOWN} precision, and a non-{@code UNKNOWN} precision
+     * requires a date. Validated in-service so the caller gets a structured 400 instead of
+     * the database constraint's raw 500.
+     *
+     * @param side human-readable field label woven into the error message ("birth", "from", …)
+     */
+    public static void requireCoherence(LocalDate date, DatePrecision precision, String side) {
+        if (date != null && (precision == null || precision == DatePrecision.UNKNOWN)) {
+            throw DomainException.badRequest(ErrorCode.INVALID_DATE_PRECISION,
+                    side + " date is set but its precision is missing or UNKNOWN");
+        }
+        if (date == null && precision != null && precision != DatePrecision.UNKNOWN) {
+            throw DomainException.badRequest(ErrorCode.INVALID_DATE_PRECISION,
+                    side + " date precision " + precision + " is set without a date");
+        }
+    }
+
+    /** A null precision means "no precision recorded" → {@link DatePrecision#UNKNOWN}. */
+    public static DatePrecision normalize(DatePrecision precision) {
+        return precision == null ? DatePrecision.UNKNOWN : precision;
+    }
+}

backend/src/main/java/org/raddatz/familienarchiv/exception/ErrorCode.java

@@ -122,6 +122,8 @@ public enum ErrorCode {
     CIRCULAR_RELATIONSHIP,
     /** A relationship with the same (person, relatedPerson, type) already exists. 409 */
     DUPLICATE_RELATIONSHIP,
+    /** A relationship's toDate is before its fromDate. 400 */
+    INVALID_RELATIONSHIP_DATES,
 
     // --- Geschichten (Stories) ---
     /** A Geschichte (story) with the given ID does not exist, or is a DRAFT and the caller lacks BLOG_WRITE. 404 */

backend/src/main/java/org/raddatz/familienarchiv/importing/PersonTreeImporter.java

@@ -13,7 +13,7 @@ import org.raddatz.familienarchiv.person.PersonType;
 import org.raddatz.familienarchiv.person.PersonUpsertCommand;
 import org.raddatz.familienarchiv.person.relationship.RelationType;
 import org.raddatz.familienarchiv.person.relationship.RelationshipService;
-import org.raddatz.familienarchiv.person.relationship.dto.CreateRelationshipRequest;
+import org.raddatz.familienarchiv.person.relationship.dto.RelationshipUpsertRequest;
 import org.springframework.stereotype.Component;
 
 import java.io.File;
@@ -126,7 +126,7 @@ public class PersonTreeImporter {
     private boolean addRelationshipIdempotently(UUID person, UUID related, String type) {
         try {
             relationshipService.addRelationship(person,
-                    new CreateRelationshipRequest(related, RelationType.valueOf(type), null, null, null));
+                    new RelationshipUpsertRequest(related, RelationType.valueOf(type), null, null, null, null, null));
             return true;
         } catch (DomainException e) {
             if (e.getCode() == ErrorCode.DUPLICATE_RELATIONSHIP

backend/src/main/java/org/raddatz/familienarchiv/person/PersonService.java

@@ -18,6 +18,7 @@ import org.raddatz.familienarchiv.person.PersonNameAliasDTO;
 import org.raddatz.familienarchiv.person.PersonSummaryDTO;
 import org.raddatz.familienarchiv.person.PersonUpdateDTO;
 import org.raddatz.familienarchiv.document.DatePrecision;
+import org.raddatz.familienarchiv.document.DatePrecisionValidation;
 import org.raddatz.familienarchiv.exception.DomainException;
 import org.raddatz.familienarchiv.exception.ErrorCode;
 import org.raddatz.familienarchiv.person.Person;
@@ -448,41 +449,28 @@ public class PersonService {
                 .alias(dto.getAlias() == null || dto.getAlias().isBlank() ? null : dto.getAlias().trim())
                 .notes(dto.getNotes() == null || dto.getNotes().isBlank() ? null : dto.getNotes().trim())
                 .birthDate(dto.getBirthDate())
-                .birthDatePrecision(normalizePrecision(dto.getBirthDatePrecision()))
+                .birthDatePrecision(DatePrecisionValidation.normalize(dto.getBirthDatePrecision()))
                 .deathDate(dto.getDeathDate())
-                .deathDatePrecision(normalizePrecision(dto.getDeathDatePrecision()))
+                .deathDatePrecision(DatePrecisionValidation.normalize(dto.getDeathDatePrecision()))
                 .generation(dto.getGeneration())
                 .build();
         return personRepository.save(person);
     }
 
     // Cross-field invariants the V76 CHECK constraints also enforce — validated here so the
-    // user gets a structured ErrorCode instead of a raw constraint-violation 500.
+    // user gets a structured ErrorCode instead of a raw constraint-violation 500. Coherence
+    // is shared with the relationship domain (DatePrecisionValidation); only the order check
+    // (and its BIRTH_AFTER_DEATH code) is life-date specific.
     private void validateLifeDates(LocalDate birthDate, DatePrecision birthPrecision,
                                    LocalDate deathDate, DatePrecision deathPrecision) {
-        requireDatePrecisionCoherence(birthDate, birthPrecision, "birth");
+        DatePrecisionValidation.requireCoherence(birthDate, birthPrecision, "birth");
-        requireDatePrecisionCoherence(deathDate, deathPrecision, "death");
+        DatePrecisionValidation.requireCoherence(deathDate, deathPrecision, "death");
         if (birthDate != null && deathDate != null && birthDate.isAfter(deathDate)) {
             throw DomainException.badRequest(ErrorCode.BIRTH_AFTER_DEATH,
                     "Birth date " + birthDate + " is after death date " + deathDate);
         }
     }
 
-    private static void requireDatePrecisionCoherence(LocalDate date, DatePrecision precision, String side) {
-        if (date != null && (precision == null || precision == DatePrecision.UNKNOWN)) {
-            throw DomainException.badRequest(ErrorCode.INVALID_DATE_PRECISION,
-                    side + " date is set but its precision is missing or UNKNOWN");
-        }
-        if (date == null && precision != null && precision != DatePrecision.UNKNOWN) {
-            throw DomainException.badRequest(ErrorCode.INVALID_DATE_PRECISION,
-                    side + " date precision " + precision + " is set without a date");
-        }
-    }
-
-    private static DatePrecision normalizePrecision(DatePrecision precision) {
-        return precision == null ? DatePrecision.UNKNOWN : precision;
-    }
-
     @Transactional
     public Person updatePerson(UUID id, PersonUpdateDTO dto) {
         if (dto.getPersonType() == PersonType.SKIP) {
@@ -499,9 +487,9 @@ public class PersonService {
         person.setAlias(dto.getAlias() == null || dto.getAlias().isBlank() ? null : dto.getAlias().trim());
         person.setNotes(dto.getNotes() == null || dto.getNotes().isBlank() ? null : dto.getNotes().trim());
         person.setBirthDate(dto.getBirthDate());
-        person.setBirthDatePrecision(normalizePrecision(dto.getBirthDatePrecision()));
+        person.setBirthDatePrecision(DatePrecisionValidation.normalize(dto.getBirthDatePrecision()));
         person.setDeathDate(dto.getDeathDate());
-        person.setDeathDatePrecision(normalizePrecision(dto.getDeathDatePrecision()));
+        person.setDeathDatePrecision(DatePrecisionValidation.normalize(dto.getDeathDatePrecision()));
         // Form path: a human can clear generation back to null. Unlike the importer
         // which routes through preferHuman, we write the DTO value verbatim.
         person.setGeneration(dto.getGeneration());

backend/src/main/java/org/raddatz/familienarchiv/person/relationship/PersonRelationship.java

@@ -5,9 +5,11 @@ import io.swagger.v3.oas.annotations.media.Schema;
 import jakarta.persistence.*;
 import lombok.*;
 import org.hibernate.annotations.CreationTimestamp;
+import org.raddatz.familienarchiv.document.DatePrecision;
 import org.raddatz.familienarchiv.person.Person;
 
 import java.time.Instant;
+import java.time.LocalDate;
 import java.util.UUID;
 
 @Entity
@@ -39,11 +41,25 @@ public class PersonRelationship {
     @Schema(requiredMode = Schema.RequiredMode.REQUIRED)
     private RelationType relationType;
 
-    @Column(name = "from_year")
+    // Start/end of the relationship (wedding, employment start, …). The date column
-    private Integer fromYear;
+    // is nullable, the precision column is NOT NULL with UNKNOWN meaning "no date" —
+    // the V78 CHECK constraints enforce (date IS NULL) = (precision = UNKNOWN) and
+    // from_date <= to_date. Mirrors Person.{birth,death}Date (ADR-039 / ADR-044).
+    private LocalDate fromDate;
 
-    @Column(name = "to_year")
+    @Enumerated(EnumType.STRING)
-    private Integer toYear;
+    @Column(name = "from_date_precision", nullable = false, length = 16)
+    @Builder.Default
+    @Schema(requiredMode = Schema.RequiredMode.REQUIRED)
+    private DatePrecision fromDatePrecision = DatePrecision.UNKNOWN;
+
+    private LocalDate toDate;
+
+    @Enumerated(EnumType.STRING)
+    @Column(name = "to_date_precision", nullable = false, length = 16)
+    @Builder.Default
+    @Schema(requiredMode = Schema.RequiredMode.REQUIRED)
+    private DatePrecision toDatePrecision = DatePrecision.UNKNOWN;
 
     @Column(length = 2000)
     private String notes;

backend/src/main/java/org/raddatz/familienarchiv/person/relationship/RelationshipController.java

@@ -3,7 +3,7 @@ package org.raddatz.familienarchiv.person.relationship;
 import jakarta.validation.Valid;
 import lombok.RequiredArgsConstructor;
 import org.raddatz.familienarchiv.person.Person;
-import org.raddatz.familienarchiv.person.relationship.dto.CreateRelationshipRequest;
+import org.raddatz.familienarchiv.person.relationship.dto.RelationshipUpsertRequest;
 import org.raddatz.familienarchiv.person.relationship.dto.FamilyMemberPatchDTO;
 import org.raddatz.familienarchiv.person.relationship.dto.InferredRelationshipDTO;
 import org.raddatz.familienarchiv.person.relationship.dto.InferredRelationshipWithPersonDTO;
@@ -63,11 +63,20 @@ public class RelationshipController {
     @RequirePermission(Permission.WRITE_ALL)
     public ResponseEntity<RelationshipDTO> addRelationship(
             @PathVariable UUID id,
-            @Valid @RequestBody CreateRelationshipRequest dto) {
+            @Valid @RequestBody RelationshipUpsertRequest dto) {
         return ResponseEntity.status(HttpStatus.CREATED)
                 .body(relationshipService.addRelationship(id, dto));
     }
 
+    @PutMapping("/api/persons/{id}/relationships/{relId}")
+    @RequirePermission(Permission.WRITE_ALL)
+    public RelationshipDTO updateRelationship(
+            @PathVariable UUID id,
+            @PathVariable UUID relId,
+            @Valid @RequestBody RelationshipUpsertRequest dto) {
+        return relationshipService.updateRelationship(id, relId, dto);
+    }
+
     @DeleteMapping("/api/persons/{id}/relationships/{relId}")
     @ResponseStatus(HttpStatus.NO_CONTENT)
     @RequirePermission(Permission.WRITE_ALL)

backend/src/main/java/org/raddatz/familienarchiv/person/relationship/RelationshipService.java

@@ -1,10 +1,12 @@
 package org.raddatz.familienarchiv.person.relationship;
 
 import lombok.RequiredArgsConstructor;
+import org.raddatz.familienarchiv.document.DatePrecision;
+import org.raddatz.familienarchiv.document.DatePrecisionValidation;
 import org.raddatz.familienarchiv.exception.DomainException;
 import org.raddatz.familienarchiv.exception.ErrorCode;
 import org.raddatz.familienarchiv.person.Person;
-import org.raddatz.familienarchiv.person.relationship.dto.CreateRelationshipRequest;
+import org.raddatz.familienarchiv.person.relationship.dto.RelationshipUpsertRequest;
 import org.raddatz.familienarchiv.person.relationship.dto.InferredRelationshipDTO;
 import org.raddatz.familienarchiv.person.relationship.dto.InferredRelationshipWithPersonDTO;
 import org.raddatz.familienarchiv.person.relationship.dto.NetworkDTO;
@@ -96,65 +98,129 @@ public class RelationshipService {
     }
 
     @Transactional
-    public RelationshipDTO addRelationship(UUID personId, CreateRelationshipRequest dto) {
+    public RelationshipDTO addRelationship(UUID personId, RelationshipUpsertRequest dto) {
-        if (personId.equals(dto.relatedPersonId())) {
+        requireNotSelf(personId, dto.relatedPersonId());
-            throw DomainException.badRequest(
-                    ErrorCode.VALIDATION_ERROR, "Cannot relate a person to themselves");
-        }
         Person person = personService.getById(personId);
         Person relatedPerson = personService.getById(dto.relatedPersonId());
 
-        validateYears(dto.fromYear(), dto.toYear());
+        validateRelationshipDates(dto.fromDate(), dto.fromDatePrecision(), dto.toDate(), dto.toDatePrecision());
-
+        requireNoReverseParent(person.getId(), relatedPerson.getId(), dto.relationType());
-        if (dto.relationType() == RelationType.PARENT_OF
-                && relationshipRepository.existsByPersonIdAndRelatedPersonIdAndRelationType(
-                        relatedPerson.getId(), personId, RelationType.PARENT_OF)) {
-            throw DomainException.conflict(
-                    ErrorCode.CIRCULAR_RELATIONSHIP,
-                    "Reverse PARENT_OF already exists between " + personId + " and " + relatedPerson.getId());
-        }
 
         PersonRelationship rel = PersonRelationship.builder()
                 .person(person)
                 .relatedPerson(relatedPerson)
                 .relationType(dto.relationType())
-                .fromYear(dto.fromYear())
+                .fromDate(dto.fromDate())
-                .toYear(dto.toYear())
+                .fromDatePrecision(DatePrecisionValidation.normalize(dto.fromDatePrecision()))
+                .toDate(dto.toDate())
+                .toDatePrecision(DatePrecisionValidation.normalize(dto.toDatePrecision()))
                 .notes(blankToNull(dto.notes()))
                 .build();
 
-        PersonRelationship saved;
+        PersonRelationship saved = persistOrConflict(rel, person.getId(), relatedPerson.getId(), dto.relationType());
-        try {
+        flagFamilyMembership(dto.relationType(), person.getId(), relatedPerson.getId());
-            // saveAndFlush so the unique_rel constraint violates synchronously and is
-            // caught here, not at commit time outside the @Transactional boundary.
-            saved = relationshipRepository.saveAndFlush(rel);
-        } catch (DataIntegrityViolationException e) {
-            throw DomainException.conflict(
-                    ErrorCode.DUPLICATE_RELATIONSHIP,
-                    "Relationship already exists for (" + personId + ", " + relatedPerson.getId() + ", " + dto.relationType() + ")");
-        }
-        // Family-graph edges imply both endpoints are family members. Idempotent: the
-        // setter is a no-op when the person is already flagged, so re-imports stay clean.
-        if (FAMILY_RELATION_TYPES.contains(dto.relationType())) {
-            personService.setFamilyMember(person.getId(), true);
-            personService.setFamilyMember(relatedPerson.getId(), true);
-        }
         return toDTO(saved);
     }
 
+    @Transactional
+    public RelationshipDTO updateRelationship(UUID personId, UUID relId, RelationshipUpsertRequest dto) {
+        PersonRelationship rel = loadOwnedRelationship(personId, relId);
+
+        // The other party from {personId}'s viewpoint cannot be {personId} itself.
+        requireNotSelf(personId, dto.relatedPersonId());
+        validateRelationshipDates(dto.fromDate(), dto.fromDatePrecision(), dto.toDate(), dto.toDatePrecision());
+
+        // Preserve the directed orientation: {personId} keeps whichever role (subject or
+        // object) it already holds on the row, and the edited "related person" takes the
+        // other role. So a PARENT_OF edge stays parent→child whether the curator edits it
+        // from the parent's page or the child's.
+        boolean viewpointIsSubject = personId.equals(rel.getPerson().getId());
+        Person viewpoint = viewpointIsSubject ? rel.getPerson() : rel.getRelatedPerson();
+        Person other = personService.getById(dto.relatedPersonId());
+        Person newSubject = viewpointIsSubject ? viewpoint : other;
+        Person newObject = viewpointIsSubject ? other : viewpoint;
+
+        requireNoReverseParent(newSubject.getId(), newObject.getId(), dto.relationType());
+
+        rel.setPerson(newSubject);
+        rel.setRelatedPerson(newObject);
+        rel.setRelationType(dto.relationType());
+        rel.setFromDate(dto.fromDate());
+        rel.setFromDatePrecision(DatePrecisionValidation.normalize(dto.fromDatePrecision()));
+        rel.setToDate(dto.toDate());
+        rel.setToDatePrecision(DatePrecisionValidation.normalize(dto.toDatePrecision()));
+        rel.setNotes(blankToNull(dto.notes()));
+
+        PersonRelationship saved = persistOrConflict(rel, newSubject.getId(), newObject.getId(), dto.relationType());
+        flagFamilyMembership(dto.relationType(), newSubject.getId(), newObject.getId());
+        return toDTO(saved);
+    }
+
+    // --- shared create/update invariants ---------------------------------------------
+
+    // A person cannot be related to themselves, from either viewpoint.
+    private static void requireNotSelf(UUID viewpointId, UUID relatedPersonId) {
+        if (viewpointId.equals(relatedPersonId)) {
+            throw DomainException.badRequest(
+                    ErrorCode.VALIDATION_ERROR, "Cannot relate a person to themselves");
+        }
+    }
+
+    // A PARENT_OF edge must not already have its mirror (child PARENT_OF parent) stored —
+    // that would be a cycle. No-op for every other relation type.
+    private void requireNoReverseParent(UUID subjectId, UUID objectId, RelationType type) {
+        if (type == RelationType.PARENT_OF
+                && relationshipRepository.existsByPersonIdAndRelatedPersonIdAndRelationType(
+                        objectId, subjectId, RelationType.PARENT_OF)) {
+            throw DomainException.conflict(
+                    ErrorCode.CIRCULAR_RELATIONSHIP,
+                    "Reverse PARENT_OF already exists between " + subjectId + " and " + objectId);
+        }
+    }
+
+    // saveAndFlush so the unique_rel constraint violates synchronously and is caught here,
+    // inside the @Transactional boundary, not at commit time as a raw 500.
+    private PersonRelationship persistOrConflict(PersonRelationship rel, UUID subjectId, UUID objectId, RelationType type) {
+        try {
+            return relationshipRepository.saveAndFlush(rel);
+        } catch (DataIntegrityViolationException e) {
+            throw DomainException.conflict(
+                    ErrorCode.DUPLICATE_RELATIONSHIP,
+                    "Relationship already exists for (" + subjectId + ", " + objectId + ", " + type + ")");
+        }
+    }
+
+    // Family-graph edges imply both endpoints are family members. Idempotent (the setter is
+    // a no-op when already flagged, so re-imports stay clean) and additive — an edit never
+    // auto-unflags.
+    private void flagFamilyMembership(RelationType type, UUID subjectId, UUID objectId) {
+        if (FAMILY_RELATION_TYPES.contains(type)) {
+            personService.setFamilyMember(subjectId, true);
+            personService.setFamilyMember(objectId, true);
+        }
+    }
+
     @Transactional
     public void deleteRelationship(UUID personId, UUID relId) {
+        PersonRelationship rel = loadOwnedRelationship(personId, relId);
+        relationshipRepository.delete(rel);
+    }
+
+    // Loads the row and verifies {personId} is one of its endpoints. A mismatch is 404
+    // (not 403): an anti-enumeration choice so a curator cannot probe relationship ids
+    // belonging to people they cannot see. Shared by update + delete for consistency.
+    private PersonRelationship loadOwnedRelationship(UUID personId, UUID relId) {
         PersonRelationship rel = relationshipRepository.findById(relId)
                 .orElseThrow(() -> DomainException.notFound(
                         ErrorCode.RELATIONSHIP_NOT_FOUND, "Relationship not found: " + relId));
-
         UUID storageSubject = rel.getPerson().getId();
         UUID storageObject = rel.getRelatedPerson().getId();
         if (!personId.equals(storageSubject) && !personId.equals(storageObject)) {
-            throw DomainException.forbidden(
+            throw DomainException.notFound(
+                    ErrorCode.RELATIONSHIP_NOT_FOUND,
                     "Relationship " + relId + " does not belong to person " + personId);
         }
-        relationshipRepository.delete(rel);
+        return rel;
     }
 
     @Transactional
@@ -173,10 +239,17 @@ public class RelationshipService {
         return date != null ? date.getYear() : null;
     }
 
-    private static void validateYears(Integer fromYear, Integer toYear) {
+    // Mirrors PersonService.validateLifeDates (ADR-039/044): coherence first so the
-        if (fromYear != null && toYear != null && toYear < fromYear) {
+    // user gets a structured 400 instead of the DB CHECK constraint's 500, then order.
-            throw DomainException.badRequest(
+    // Coherence is shared with the person domain (DatePrecisionValidation); only the order
-                    ErrorCode.VALIDATION_ERROR, "toYear must not be before fromYear");
+    // check (and its INVALID_RELATIONSHIP_DATES code) is relationship specific.
+    private static void validateRelationshipDates(LocalDate fromDate, DatePrecision fromPrecision,
+                                                  LocalDate toDate, DatePrecision toPrecision) {
+        DatePrecisionValidation.requireCoherence(fromDate, fromPrecision, "from");
+        DatePrecisionValidation.requireCoherence(toDate, toPrecision, "to");
+        if (fromDate != null && toDate != null && toDate.isBefore(fromDate)) {
+            throw DomainException.badRequest(ErrorCode.INVALID_RELATIONSHIP_DATES,
+                    "toDate " + toDate + " is before fromDate " + fromDate);
         }
     }
 
@@ -194,8 +267,10 @@ public class RelationshipService {
                 yearOf(rp.getBirthDate()),
                 yearOf(rp.getDeathDate()),
                 r.getRelationType(),
-                r.getFromYear(),
+                r.getFromDate(),
-                r.getToYear(),
+                r.getFromDatePrecision(),
+                r.getToDate(),
+                r.getToDatePrecision(),
                 r.getNotes());
     }
 }

backend/src/main/java/org/raddatz/familienarchiv/person/relationship/dto/CreateRelationshipRequest.java

@@ -1,15 +0,0 @@
-package org.raddatz.familienarchiv.person.relationship.dto;
-
-import jakarta.validation.constraints.NotNull;
-import jakarta.validation.constraints.Size;
-import org.raddatz.familienarchiv.person.relationship.RelationType;
-
-import java.util.UUID;
-
-public record CreateRelationshipRequest(
-        @NotNull UUID relatedPersonId,
-        @NotNull RelationType relationType,
-        Integer fromYear,
-        Integer toYear,
-        @Size(max = 2000) String notes
-) {}

backend/src/main/java/org/raddatz/familienarchiv/person/relationship/dto/RelationshipDTO.java

@@ -1,8 +1,10 @@
 package org.raddatz.familienarchiv.person.relationship.dto;
 
 import io.swagger.v3.oas.annotations.media.Schema;
+import org.raddatz.familienarchiv.document.DatePrecision;
 import org.raddatz.familienarchiv.person.relationship.RelationType;
 
+import java.time.LocalDate;
 import java.util.UUID;
 
 /**
@@ -26,7 +28,9 @@ public record RelationshipDTO(
         Integer relatedPersonBirthYear,
         Integer relatedPersonDeathYear,
         @Schema(requiredMode = Schema.RequiredMode.REQUIRED) RelationType relationType,
-        Integer fromYear,
+        LocalDate fromDate,
-        Integer toYear,
+        @Schema(requiredMode = Schema.RequiredMode.REQUIRED) DatePrecision fromDatePrecision,
+        LocalDate toDate,
+        @Schema(requiredMode = Schema.RequiredMode.REQUIRED) DatePrecision toDatePrecision,
         String notes
 ) {}

backend/src/main/java/org/raddatz/familienarchiv/person/relationship/dto/RelationshipUpsertRequest.java

@@ -0,0 +1,26 @@
+package org.raddatz.familienarchiv.person.relationship.dto;
+
+import jakarta.validation.constraints.NotNull;
+import jakarta.validation.constraints.Size;
+import org.raddatz.familienarchiv.document.DatePrecision;
+import org.raddatz.familienarchiv.person.relationship.RelationType;
+
+import java.time.LocalDate;
+import java.util.UUID;
+
+/**
+ * Request body for both creating and updating a relationship — the fields are
+ * identical, so one record serves {@code POST} and {@code PUT} (DRY). A null
+ * {@code *DatePrecision} is normalized to {@code UNKNOWN} by the service; the
+ * service then enforces coherence (date ⇔ non-UNKNOWN precision) and order
+ * (fromDate ≤ toDate).
+ */
+public record RelationshipUpsertRequest(
+        @NotNull UUID relatedPersonId,
+        @NotNull RelationType relationType,
+        LocalDate fromDate,
+        DatePrecision fromDatePrecision,
+        LocalDate toDate,
+        DatePrecision toDatePrecision,
+        @Size(max = 2000) String notes
+) {}

backend/src/main/java/org/raddatz/familienarchiv/timeline/TimelineEntryDTO.java

@@ -28,6 +28,13 @@ import java.util.UUID;
  * They are deliberately NOT {@code @Schema(requiredMode = REQUIRED)} so the generated TypeScript
  * types stay optional.
  *
+ * <p><b>Letter→event link ({@code linkedEventId}):</b> for a {@link Kind#LETTER} entry, the id of
+ * the curated {@link TimelineEvent} whose {@code documents} set contains the letter's document, or
+ * {@code null} when the letter is referenced by no curated event (#827). Computed on read from the
+ * existing {@code timeline_event_documents} join — no new column. {@code null} for non-letter
+ * entries. Deliberately NOT {@code @Schema(requiredMode = REQUIRED)} so the generated TypeScript
+ * type stays optional.
+ *
  * <p>Callers of {@code TimelineEventService.assembleDerivedEvents()} must independently enforce
  * {@code READ_ALL} authorization before invoking that method (see ADR-043).
  */
@@ -47,6 +54,7 @@ public record TimelineEntryDTO(
         DerivedEventType derivedType,
         UUID rootTagId,
         String rootTagName,
-        String rootTagColor
+        String rootTagColor,
+        UUID linkedEventId
 ) {
 }

backend/src/main/java/org/raddatz/familienarchiv/timeline/TimelineEventService.java

@@ -267,7 +267,7 @@ public class TimelineEventService {
                         p.getBirthDate(), null,
                         p.getDisplayName(), EventType.PERSONAL,
                         null, null, List.of(p.getId()), DerivedEventType.BIRTH,
-                        null, null, null))
+                        null, null, null, null))
                 .toList();
     }
 
@@ -279,7 +279,7 @@ public class TimelineEventService {
                         p.getDeathDate(), null,
                         p.getDisplayName(), EventType.PERSONAL,
                         null, null, List.of(p.getId()), DerivedEventType.DEATH,
-                        null, null, null))
+                        null, null, null, null))
                 .toList();
     }
 
@@ -290,13 +290,11 @@ public class TimelineEventService {
         List<TimelineEntryDTO> result = new ArrayList<>();
         for (PersonRelationship r : spouseEdges) {
             if (seen.add(r.getId())) {
-                // JOIN FETCH in findAllSpouseEdges() guarantees person/relatedPerson are loaded
+                // JOIN FETCH in findAllSpouseEdges() guarantees person/relatedPerson are loaded.
-                LocalDate eventDate = r.getFromYear() != null
+                // The marriage date is the relationship's from_date at its stored precision
-                        ? LocalDate.of(r.getFromYear(), 1, 1)
+                // (ADR-044): a DAY-precision wedding now surfaces the exact day, not just the year.
-                        : null;
+                LocalDate eventDate = r.getFromDate();
-                DatePrecision precision = r.getFromYear() != null
+                DatePrecision precision = r.getFromDatePrecision();
-                        ? DatePrecision.YEAR
-                        : DatePrecision.UNKNOWN;
                 String title = r.getPerson().getDisplayName()
                         + " & " + r.getRelatedPerson().getDisplayName();
                 result.add(new TimelineEntryDTO(
@@ -306,7 +304,7 @@ public class TimelineEventService {
                         null, null,
                         List.of(r.getPerson().getId(), r.getRelatedPerson().getId()),
                         DerivedEventType.MARRIAGE,
-                        null, null, null));
+                        null, null, null, null));
             }
         }
         return result;

backend/src/main/java/org/raddatz/familienarchiv/timeline/TimelineService.java

@@ -80,9 +80,14 @@ public class TimelineService {
         // Resolve generation person IDs once — used across all three layers
         Set<UUID> genPersonIds = resolveGenerationPersonIds(filter.generation());
 
+        // Fetch curated events once — reused for both the event entries below and the
+        // batched letter→event link resolution (resolveLetterEventLinks), so the
+        // membership pass costs no extra query. REQ-005.
+        List<TimelineEvent> allEvents = eventRepository.findAll();
+
         // ── curated events ───────────────────────────────────────────────────
         List<TimelineEntryDTO> entries = new ArrayList<>();
-        for (TimelineEvent ev : eventRepository.findAll()) {
+        for (TimelineEvent ev : allEvents) {
             if (!passesTypeFilter(ev.getType(), filter.type())) continue;
             if (!passesPersonFilter(ev.getPersons(), filter.personId())) continue;
             if (!passesGenerationFilter(ev.getPersons(), genPersonIds)) continue;
@@ -107,8 +112,9 @@ public class TimelineService {
             letters.add(doc);
         }
         Map<UUID, RootTag> rootByDocId = resolveLetterRootTags(letters);
+        Map<UUID, UUID> eventByDocId = resolveLetterEventLinks(letters, allEvents);
         for (Document doc : letters) {
-            entries.add(mapDocument(doc, rootByDocId));
+            entries.add(mapDocument(doc, rootByDocId, eventByDocId));
         }
 
         return bucket(entries);
@@ -229,11 +235,13 @@ public class TimelineService {
                 null,
                 null,
                 null,
+                null,
                 null
         );
     }
 
-    private TimelineEntryDTO mapDocument(Document doc, Map<UUID, RootTag> rootByDocId) {
+    private TimelineEntryDTO mapDocument(Document doc, Map<UUID, RootTag> rootByDocId,
+                                         Map<UUID, UUID> eventByDocId) {
         RootTag root = rootByDocId.get(doc.getId());
         return new TimelineEntryDTO(
                 Kind.LETTER,
@@ -251,10 +259,38 @@ public class TimelineService {
                 null,
                 root == null ? null : root.id(),
                 root == null ? null : root.name(),
-                root == null ? null : root.color()
+                root == null ? null : root.color(),
+                eventByDocId.get(doc.getId())
         );
     }
 
+    /**
+     * Resolves each letter's linked curated event in one batched pass, keyed by document id: the
+     * event whose {@code documents} set contains the letter (REQ-005). A single doc→event map is
+     * built over the already-loaded events — no per-letter query ({@code TimelineEvent.documents}
+     * carries {@code @BatchSize(50)}). When a document is referenced by more than one curated
+     * event, the first by repository iteration order wins ({@code putIfAbsent}). The map is built
+     * from <em>all</em> events (not just the year/type-filtered ones) so the link is a stable
+     * property of the data; the frontend's filter-then-group decides whether the linked event is
+     * actually on screen (#827). Logs nothing — the assembly path keeps UUIDs out of logs (§2.7).
+     */
+    private Map<UUID, UUID> resolveLetterEventLinks(List<Document> letters, List<TimelineEvent> events) {
+        Set<UUID> letterDocIds = letters.stream().map(Document::getId).collect(Collectors.toSet());
+        if (letterDocIds.isEmpty()) return Map.of();
+
+        Map<UUID, UUID> eventByDocId = new HashMap<>();
+        for (TimelineEvent ev : events) {
+            Set<Document> linkedDocs = ev.getDocuments();
+            if (linkedDocs == null) continue;
+            for (Document linked : linkedDocs) {
+                if (letterDocIds.contains(linked.getId())) {
+                    eventByDocId.putIfAbsent(linked.getId(), ev.getId());
+                }
+            }
+        }
+        return eventByDocId;
+    }
+
     /**
      * Resolves each letter's primary root tag in one batched pass, keyed by document id — no
      * per-letter N+1: each letter contributes only its alphabetically-first assigned tag (#835),

backend/src/main/resources/db/migration/V78__relationship_years_to_localdate.sql

@@ -0,0 +1,43 @@
+-- V78: person_relationships.from_year/to_year (integer) → from_date/to_date (date)
+-- plus NOT NULL precision columns, mirroring persons.{birth,death}_date (V76 / ADR-039).
+-- Existing years are backfilled as YYYY-01-01 at YEAR precision (ADR-044).
+-- One-way migration: rollback is a targeted pg_restore -t person_relationships from
+-- the pre-deploy backup (see docs/DEPLOYMENT.md). The column drop is NOT
+-- rolling-deploy-safe — stop the old JAR before running this migration.
+
+-- Pre-check (data quality gate — not a race guard): abort on corrupt year data
+-- before any DDL runs. Single-writer family archive, so no race window matters.
+DO $$ BEGIN
+  IF EXISTS (SELECT 1 FROM person_relationships WHERE from_year IS NOT NULL AND to_year IS NOT NULL AND from_year > to_year)
+    THEN RAISE EXCEPTION 'V78 aborted: % relationships have from_year > to_year — fix data before migrating',
+      (SELECT COUNT(*) FROM person_relationships WHERE from_year IS NOT NULL AND to_year IS NOT NULL AND from_year > to_year);
+  END IF;
+  IF EXISTS (SELECT 1 FROM person_relationships WHERE from_year = 0 OR to_year = 0)
+    THEN RAISE EXCEPTION 'V78 aborted: person_relationships table contains from_year=0 or to_year=0 rows — clean data before migrating';
+  END IF;
+END $$;
+
+ALTER TABLE person_relationships ADD COLUMN from_date date;
+ALTER TABLE person_relationships ADD COLUMN from_date_precision varchar(16) NOT NULL DEFAULT 'UNKNOWN';
+ALTER TABLE person_relationships ADD COLUMN to_date date;
+ALTER TABLE person_relationships ADD COLUMN to_date_precision varchar(16) NOT NULL DEFAULT 'UNKNOWN';
+
+UPDATE person_relationships SET from_date = make_date(from_year, 1, 1), from_date_precision = 'YEAR'
+    WHERE from_year IS NOT NULL;
+UPDATE person_relationships SET to_date = make_date(to_year, 1, 1), to_date_precision = 'YEAR'
+    WHERE to_year IS NOT NULL;
+
+-- Named constraints: readable Postgres error messages when violated.
+ALTER TABLE person_relationships ADD CONSTRAINT chk_relationship_from_coherence
+    CHECK ((from_date IS NULL) = (from_date_precision = 'UNKNOWN'));
+ALTER TABLE person_relationships ADD CONSTRAINT chk_relationship_to_coherence
+    CHECK ((to_date IS NULL) = (to_date_precision = 'UNKNOWN'));
+ALTER TABLE person_relationships ADD CONSTRAINT chk_relationship_date_order
+    CHECK (from_date IS NULL OR to_date IS NULL OR from_date <= to_date);
+ALTER TABLE person_relationships ADD CONSTRAINT chk_relationship_from_precision_values
+    CHECK (from_date_precision IN ('DAY', 'MONTH', 'SEASON', 'YEAR', 'RANGE', 'APPROX', 'UNKNOWN'));
+ALTER TABLE person_relationships ADD CONSTRAINT chk_relationship_to_precision_values
+    CHECK (to_date_precision IN ('DAY', 'MONTH', 'SEASON', 'YEAR', 'RANGE', 'APPROX', 'UNKNOWN'));
+
+ALTER TABLE person_relationships DROP COLUMN from_year;
+ALTER TABLE person_relationships DROP COLUMN to_year;

backend/src/test/java/org/raddatz/familienarchiv/importing/CanonicalImportOrchestratorTest.java

@@ -6,6 +6,7 @@ import org.junit.jupiter.api.io.TempDir;
 import org.mockito.InOrder;
 import org.mockito.Mock;
 import org.mockito.junit.jupiter.MockitoExtension;
+import org.raddatz.familienarchiv.document.DatePrecision;
 import org.raddatz.familienarchiv.exception.DomainException;
 import org.raddatz.familienarchiv.person.relationship.RelationType;
 import org.raddatz.familienarchiv.person.relationship.RelationshipService;
@@ -169,7 +170,7 @@ class CanonicalImportOrchestratorTest {
         RelationshipDTO edge = new RelationshipDTO(
                 UUID.randomUUID(), parentId, childId,
                 "Parent", null, null, "Child", null, null,
-                RelationType.PARENT_OF, null, null, null);
+                RelationType.PARENT_OF, null, DatePrecision.UNKNOWN, null, DatePrecision.UNKNOWN, null);
         when(relationshipService.getFamilyNetwork())
                 .thenReturn(new NetworkDTO(List.of(parent, child), List.of(edge)));
         when(documentImporter.load(any())).thenReturn(new DocumentImporter.LoadResult(0, List.of()));

backend/src/test/java/org/raddatz/familienarchiv/importing/PersonTreeImporterTest.java

@@ -12,7 +12,7 @@ import org.raddatz.familienarchiv.person.PersonService;
 import org.raddatz.familienarchiv.person.PersonUpsertCommand;
 import org.raddatz.familienarchiv.person.relationship.RelationType;
 import org.raddatz.familienarchiv.person.relationship.RelationshipService;
-import org.raddatz.familienarchiv.person.relationship.dto.CreateRelationshipRequest;
+import org.raddatz.familienarchiv.person.relationship.dto.RelationshipUpsertRequest;
 
 import java.nio.file.Files;
 import java.nio.file.Path;
@@ -76,7 +76,7 @@ class PersonTreeImporterTest {
         new PersonTreeImporter(personService, relationshipService)
                 .load(json.toFile());
 
-        ArgumentCaptor<CreateRelationshipRequest> captor = ArgumentCaptor.forClass(CreateRelationshipRequest.class);
+        ArgumentCaptor<RelationshipUpsertRequest> captor = ArgumentCaptor.forClass(RelationshipUpsertRequest.class);
         verify(relationshipService).addRelationship(eq(idA), captor.capture());
         assertThat(captor.getValue().relatedPersonId()).isEqualTo(idB);
         assertThat(captor.getValue().relationType()).isEqualTo(RelationType.SPOUSE_OF);

backend/src/test/java/org/raddatz/familienarchiv/person/relationship/RelationshipControllerTest.java

@@ -1,6 +1,7 @@
 package org.raddatz.familienarchiv.person.relationship;
 
 import org.junit.jupiter.api.Test;
+import org.raddatz.familienarchiv.document.DatePrecision;
 import org.raddatz.familienarchiv.security.SecurityConfig;
 import org.raddatz.familienarchiv.exception.ErrorCode;
 import org.raddatz.familienarchiv.person.relationship.dto.InferredRelationshipWithPersonDTO;
@@ -25,6 +26,8 @@ import java.util.UUID;
 
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.doNothing;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
 import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.*;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.*;
@@ -98,7 +101,7 @@ class RelationshipControllerTest {
                 UUID.randomUUID(), PERSON_ID, OTHER_ID,
                 "Alice Müller", 1900, 1980,
                 "Bob Müller", 1930, null,
-                RelationType.PARENT_OF, null, null, null);
+                RelationType.PARENT_OF, null, DatePrecision.UNKNOWN, null, DatePrecision.UNKNOWN, null);
         when(relationshipService.getFamilyNetwork())
                 .thenReturn(new NetworkDTO(List.of(node), List.of(edge)));
 
@@ -139,7 +142,7 @@ class RelationshipControllerTest {
                 UUID.randomUUID(), PERSON_ID, OTHER_ID,
                 "Alice Müller", null, null,
                 "Bob Müller", null, null,
-                RelationType.PARENT_OF, null, null, null);
+                RelationType.PARENT_OF, null, DatePrecision.UNKNOWN, null, DatePrecision.UNKNOWN, null);
         when(relationshipService.addRelationship(any(), any())).thenReturn(created);
 
         mockMvc.perform(post("/api/persons/{id}/relationships", PERSON_ID).with(csrf())
@@ -158,4 +161,51 @@ class RelationshipControllerTest {
         mockMvc.perform(delete("/api/persons/{id}/relationships/{relId}", PERSON_ID, relId).with(csrf()))
                 .andExpect(status().isNoContent());
     }
+
+    // ─── PUT /api/persons/{id}/relationships/{relId} ──────────────────────────
+
+    @Test
+    @WithMockUser(username = "testuser", authorities = {"WRITE_ALL"})
+    void updateRelationship_returns200_with_RelationshipDTO_for_WRITE_ALL_user() throws Exception {
+        UUID relId = UUID.randomUUID();
+        RelationshipDTO updated = new RelationshipDTO(
+                relId, PERSON_ID, OTHER_ID,
+                "Alice Müller", null, null,
+                "Bob Müller", null, null,
+                RelationType.SPOUSE_OF, null, DatePrecision.UNKNOWN, null, DatePrecision.UNKNOWN, null);
+        when(relationshipService.updateRelationship(any(), any(), any())).thenReturn(updated);
+
+        mockMvc.perform(put("/api/persons/{id}/relationships/{relId}", PERSON_ID, relId).with(csrf())
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"relatedPersonId\":\"" + OTHER_ID + "\",\"relationType\":\"SPOUSE_OF\"}"))
+                .andExpect(status().isOk())
+                .andExpect(jsonPath("$.relationType").value("SPOUSE_OF"));
+    }
+
+    @Test
+    void updateRelationship_returns401_whenUnauthenticated_and_does_not_touch_service() throws Exception {
+        mockMvc.perform(put("/api/persons/{id}/relationships/{relId}", PERSON_ID, UUID.randomUUID()).with(csrf())
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"relatedPersonId\":\"" + OTHER_ID + "\",\"relationType\":\"SPOUSE_OF\"}"))
+                .andExpect(status().isUnauthorized());
+        verify(relationshipService, never()).updateRelationship(any(), any(), any());
+    }
+
+    @Test
+    @WithMockUser(username = "testuser", authorities = {"READ_ALL"})
+    void updateRelationship_returns403_for_READ_ALL_only_user() throws Exception {
+        mockMvc.perform(put("/api/persons/{id}/relationships/{relId}", PERSON_ID, UUID.randomUUID()).with(csrf())
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"relatedPersonId\":\"" + OTHER_ID + "\",\"relationType\":\"SPOUSE_OF\"}"))
+                .andExpect(status().isForbidden());
+    }
+
+    @Test
+    @WithMockUser(username = "testuser", authorities = {"WRITE_ALL"})
+    void updateRelationship_returns400_when_relationType_is_unknown_value() throws Exception {
+        mockMvc.perform(put("/api/persons/{id}/relationships/{relId}", PERSON_ID, UUID.randomUUID()).with(csrf())
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"relatedPersonId\":\"" + OTHER_ID + "\",\"relationType\":\"NOT_A_REAL_TYPE\"}"))
+                .andExpect(status().isBadRequest());
+    }
 }

backend/src/test/java/org/raddatz/familienarchiv/person/relationship/RelationshipMigrationTest.java

@@ -0,0 +1,306 @@
+package org.raddatz.familienarchiv.person.relationship;
+
+import org.flywaydb.core.Flyway;
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.testcontainers.containers.PostgreSQLContainer;
+
+import java.sql.Connection;
+import java.sql.DriverManager;
+import java.sql.PreparedStatement;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.sql.Statement;
+import java.util.Map;
+import java.util.UUID;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+/**
+ * Verifies V78: person_relationships.from_year/to_year (integer) become
+ * from_date/to_date (date) + *_date_precision columns, with backfill to
+ * YYYY-01-01 at YEAR precision, named CHECK constraints, and a data-quality
+ * pre-check that aborts the migration on corrupt year data. Mirrors
+ * {@code PersonBirthDeathMigrationTest} (V76 / ADR-039).
+ *
+ * <p>Runs Flyway programmatically (no Spring context): each test gets its own
+ * database so the staged migrate-to-V77 → seed → migrate-to-latest flow and
+ * the abort cases cannot interfere with each other. Uses a real Postgres
+ * container — H2 does not honour CHECK constraints.
+ */
+class RelationshipMigrationTest {
+
+    private static final PostgreSQLContainer<?> POSTGRES = new PostgreSQLContainer<>("postgres:16-alpine");
+    private static final AtomicInteger DB_COUNTER = new AtomicInteger();
+
+    private String dbUrl;
+
+    @BeforeAll
+    static void startContainer() {
+        POSTGRES.start();
+    }
+
+    @AfterAll
+    static void stopContainer() {
+        POSTGRES.stop();
+    }
+
+    @BeforeEach
+    void createFreshDatabase() throws SQLException {
+        String dbName = "mig_v78_" + DB_COUNTER.incrementAndGet();
+        try (Connection conn = DriverManager.getConnection(
+                baseUrl("postgres"), POSTGRES.getUsername(), POSTGRES.getPassword());
+             Statement stmt = conn.createStatement()) {
+            stmt.execute("CREATE DATABASE " + dbName);
+        }
+        dbUrl = baseUrl(dbName);
+    }
+
+    @Test
+    void precheck_abortsWhenFromYearAfterToYear() throws SQLException {
+        migrateTo("77");
+        UUID a = seedPerson("Alpha");
+        UUID b = seedPerson("Beta");
+        seedRelationship(a, b, "SPOUSE_OF", 1958, 1923);
+
+        assertThatThrownBy(this::migrateToLatest)
+                .hasMessageContaining("V78 aborted")
+                .hasMessageContaining("from_year > to_year");
+    }
+
+    @Test
+    void precheck_abortsWhenYearZeroPresent() throws SQLException {
+        migrateTo("77");
+        UUID a = seedPerson("Alpha");
+        UUID b = seedPerson("Beta");
+        seedRelationship(a, b, "FRIEND", 0, null);
+
+        assertThatThrownBy(this::migrateToLatest)
+                .hasMessageContaining("V78 aborted")
+                .hasMessageContaining("from_year=0 or to_year=0");
+    }
+
+    @Test
+    void backfill_fromYearAndToYear_becomeYearPrecisionDates() throws SQLException {
+        migrateTo("77");
+        UUID a = seedPerson("Alpha");
+        UUID b = seedPerson("Beta");
+        seedRelationship(a, b, "SPOUSE_OF", 1923, 1958);
+
+        migrateToLatest();
+
+        RelationDates row = relationDates(a, b, "SPOUSE_OF");
+        assertThat(row.fromDate()).hasToString("1923-01-01");
+        assertThat(row.fromPrecision()).isEqualTo("YEAR");
+        assertThat(row.toDate()).hasToString("1958-01-01");
+        assertThat(row.toPrecision()).isEqualTo("YEAR");
+    }
+
+    @Test
+    void backfill_bothNull_leavesDatesNullAndPrecisionsUnknown() throws SQLException {
+        migrateTo("77");
+        UUID a = seedPerson("Alpha");
+        UUID b = seedPerson("Beta");
+        seedRelationship(a, b, "FRIEND", null, null);
+
+        migrateToLatest();
+
+        RelationDates row = relationDates(a, b, "FRIEND");
+        assertThat(row.fromDate()).isNull();
+        assertThat(row.fromPrecision()).isEqualTo("UNKNOWN");
+        assertThat(row.toDate()).isNull();
+        assertThat(row.toPrecision()).isEqualTo("UNKNOWN");
+    }
+
+    @Test
+    void backfill_preservesRowCount() throws SQLException {
+        migrateTo("77");
+        UUID a = seedPerson("Alpha");
+        UUID b = seedPerson("Beta");
+        UUID c = seedPerson("Gamma");
+        seedRelationship(a, b, "SPOUSE_OF", 1923, 1958);
+        seedRelationship(a, c, "FRIEND", null, null);
+
+        migrateToLatest();
+
+        assertThat(countWhere("1 = 1")).isEqualTo(2);
+    }
+
+    @Test
+    void orderCheckConstraint_rejectsToDateBeforeFromDate() throws SQLException {
+        migrateTo("77");
+        UUID a = seedPerson("Alpha");
+        UUID b = seedPerson("Beta");
+        migrateToLatest();
+
+        assertThatThrownBy(() -> insertDatedRelationship(
+                a, b, "FRIEND", "1958-01-01", "YEAR", "1923-01-01", "YEAR"))
+                .hasMessageContaining("chk_relationship_date_order");
+    }
+
+    @Test
+    void coherenceCheckConstraint_rejectsDatePresentWithUnknownPrecision() throws SQLException {
+        migrateTo("77");
+        UUID a = seedPerson("Alpha");
+        UUID b = seedPerson("Beta");
+        migrateToLatest();
+
+        assertThatThrownBy(() -> insertDatedRelationship(
+                a, b, "FRIEND", "1923-01-01", "UNKNOWN", null, "UNKNOWN"))
+                .hasMessageContaining("chk_relationship_from_coherence");
+    }
+
+    @Test
+    void yearColumnsDropped_andNamedCheckConstraintsExist() throws SQLException {
+        migrateTo("77");
+        UUID a = seedPerson("Alpha");
+        UUID b = seedPerson("Beta");
+        seedRelationship(a, b, "SPOUSE_OF", 1923, 1958);
+
+        migrateToLatest();
+
+        assertThat(columnExists("from_year")).isFalse();
+        assertThat(columnExists("to_year")).isFalse();
+        assertThat(columnExists("from_date")).isTrue();
+        assertThat(columnExists("to_date")).isTrue();
+        for (String constraint : new String[]{
+                "chk_relationship_from_coherence",
+                "chk_relationship_to_coherence",
+                "chk_relationship_date_order",
+                "chk_relationship_from_precision_values",
+                "chk_relationship_to_precision_values"}) {
+            assertThat(constraintExists(constraint)).as(constraint).isTrue();
+        }
+    }
+
+    // --- helpers ---
+
+    private static String baseUrl(String dbName) {
+        return "jdbc:postgresql://" + POSTGRES.getHost() + ":" + POSTGRES.getMappedPort(5432) + "/" + dbName;
+    }
+
+    private void migrateTo(String targetVersion) {
+        flywayBuilder().target(targetVersion).load().migrate();
+    }
+
+    private void migrateToLatest() {
+        flywayBuilder().load().migrate();
+    }
+
+    private org.flywaydb.core.api.configuration.FluentConfiguration flywayBuilder() {
+        return Flyway.configure()
+                .dataSource(dbUrl, POSTGRES.getUsername(), POSTGRES.getPassword())
+                .locations("classpath:db/migration")
+                .placeholders(Map.of("grafanaDbPassword", "test-only"));
+    }
+
+    private UUID seedPerson(String lastName) throws SQLException {
+        UUID id = UUID.randomUUID();
+        try (Connection conn = connect();
+             PreparedStatement stmt = conn.prepareStatement(
+                     "INSERT INTO persons (id, last_name, person_type, family_member, provisional) "
+                             + "VALUES (?, ?, 'PERSON', false, false)")) {
+            stmt.setObject(1, id);
+            stmt.setString(2, lastName);
+            stmt.executeUpdate();
+        }
+        return id;
+    }
+
+    private void seedRelationship(UUID personId, UUID relatedId, String type, Integer fromYear, Integer toYear)
+            throws SQLException {
+        try (Connection conn = connect();
+             PreparedStatement stmt = conn.prepareStatement(
+                     "INSERT INTO person_relationships (id, person_id, related_person_id, relation_type, from_year, to_year) "
+                             + "VALUES (gen_random_uuid(), ?, ?, ?, ?, ?)")) {
+            stmt.setObject(1, personId);
+            stmt.setObject(2, relatedId);
+            stmt.setString(3, type);
+            stmt.setObject(4, fromYear);
+            stmt.setObject(5, toYear);
+            stmt.executeUpdate();
+        }
+    }
+
+    private void insertDatedRelationship(UUID personId, UUID relatedId, String type,
+                                         String fromDate, String fromPrecision,
+                                         String toDate, String toPrecision) throws SQLException {
+        try (Connection conn = connect();
+             PreparedStatement stmt = conn.prepareStatement(
+                     "INSERT INTO person_relationships "
+                             + "(id, person_id, related_person_id, relation_type, from_date, from_date_precision, to_date, to_date_precision) "
+                             + "VALUES (gen_random_uuid(), ?, ?, ?, CAST(? AS date), ?, CAST(? AS date), ?)")) {
+            stmt.setObject(1, personId);
+            stmt.setObject(2, relatedId);
+            stmt.setString(3, type);
+            stmt.setObject(4, fromDate);
+            stmt.setString(5, fromPrecision);
+            stmt.setObject(6, toDate);
+            stmt.setString(7, toPrecision);
+            stmt.executeUpdate();
+        }
+    }
+
+    private record RelationDates(Object fromDate, String fromPrecision, Object toDate, String toPrecision) {}
+
+    private RelationDates relationDates(UUID personId, UUID relatedId, String type) throws SQLException {
+        try (Connection conn = connect();
+             PreparedStatement stmt = conn.prepareStatement(
+                     "SELECT from_date, from_date_precision, to_date, to_date_precision "
+                             + "FROM person_relationships WHERE person_id = ? AND related_person_id = ? AND relation_type = ?")) {
+            stmt.setObject(1, personId);
+            stmt.setObject(2, relatedId);
+            stmt.setString(3, type);
+            try (ResultSet rs = stmt.executeQuery()) {
+                assertThat(rs.next()).as("relationship exists").isTrue();
+                return new RelationDates(
+                        rs.getObject("from_date"),
+                        rs.getString("from_date_precision"),
+                        rs.getObject("to_date"),
+                        rs.getString("to_date_precision"));
+            }
+        }
+    }
+
+    private long countWhere(String condition) throws SQLException {
+        try (Connection conn = connect();
+             Statement stmt = conn.createStatement();
+             ResultSet rs = stmt.executeQuery("SELECT COUNT(*) FROM person_relationships WHERE " + condition)) {
+            rs.next();
+            return rs.getLong(1);
+        }
+    }
+
+    private boolean columnExists(String columnName) throws SQLException {
+        try (Connection conn = connect();
+             PreparedStatement stmt = conn.prepareStatement(
+                     "SELECT COUNT(*) FROM information_schema.columns "
+                             + "WHERE table_schema = 'public' AND table_name = 'person_relationships' AND column_name = ?")) {
+            stmt.setString(1, columnName);
+            try (ResultSet rs = stmt.executeQuery()) {
+                rs.next();
+                return rs.getInt(1) > 0;
+            }
+        }
+    }
+
+    private boolean constraintExists(String constraintName) throws SQLException {
+        try (Connection conn = connect();
+             PreparedStatement stmt = conn.prepareStatement(
+                     "SELECT COUNT(*) FROM pg_constraint WHERE conname = ?")) {
+            stmt.setString(1, constraintName);
+            try (ResultSet rs = stmt.executeQuery()) {
+                rs.next();
+                return rs.getInt(1) > 0;
+            }
+        }
+    }
+
+    private Connection connect() throws SQLException {
+        return DriverManager.getConnection(dbUrl, POSTGRES.getUsername(), POSTGRES.getPassword());
+    }
+}

backend/src/test/java/org/raddatz/familienarchiv/person/relationship/RelationshipServiceIntegrationTest.java

@@ -4,10 +4,11 @@ import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.raddatz.familienarchiv.PostgresContainerConfig;
 import org.raddatz.familienarchiv.config.FlywayConfig;
+import org.raddatz.familienarchiv.document.DatePrecision;
 import org.raddatz.familienarchiv.exception.DomainException;
 import org.raddatz.familienarchiv.exception.ErrorCode;
 import org.raddatz.familienarchiv.person.Person;
-import org.raddatz.familienarchiv.person.relationship.dto.CreateRelationshipRequest;
+import org.raddatz.familienarchiv.person.relationship.dto.RelationshipUpsertRequest;
 import org.raddatz.familienarchiv.person.relationship.dto.NetworkDTO;
 import org.raddatz.familienarchiv.person.relationship.dto.RelationshipDTO;
 import org.raddatz.familienarchiv.person.PersonNameAliasRepository;
@@ -20,6 +21,7 @@ import org.springframework.context.annotation.Import;
 
 import jakarta.persistence.EntityManager;
 
+import java.time.LocalDate;
 import java.util.List;
 import java.util.UUID;
 
@@ -65,13 +67,17 @@ class RelationshipServiceIntegrationTest {
 
     @Test
     void addRelationship_stores_and_is_readable() {
-        var dto = new CreateRelationshipRequest(bob.getId(), RelationType.PARENT_OF, 1900, null, null);
+        var dto = new RelationshipUpsertRequest(bob.getId(), RelationType.PARENT_OF,
+                LocalDate.of(1900, 1, 1), DatePrecision.YEAR, null, null, null);
 
         RelationshipDTO created = relationshipService.addRelationship(alice.getId(), dto);
 
         assertThat(created.id()).isNotNull();
         assertThat(created.personId()).isEqualTo(alice.getId());
         assertThat(created.relatedPersonId()).isEqualTo(bob.getId());
+        assertThat(created.fromDate()).isEqualTo(LocalDate.of(1900, 1, 1));
+        assertThat(created.fromDatePrecision()).isEqualTo(DatePrecision.YEAR);
+        assertThat(created.toDatePrecision()).isEqualTo(DatePrecision.UNKNOWN);
 
         List<RelationshipDTO> rels = relationshipService.getRelationships(alice.getId());
         assertThat(rels).hasSize(1);
@@ -80,7 +86,7 @@ class RelationshipServiceIntegrationTest {
 
     @Test
     void addRelationship_throws_409_when_duplicate() {
-        var dto = new CreateRelationshipRequest(bob.getId(), RelationType.PARENT_OF, null, null, null);
+        var dto = new RelationshipUpsertRequest(bob.getId(), RelationType.PARENT_OF, null, null, null, null, null);
         relationshipService.addRelationship(alice.getId(), dto);
 
         assertThatThrownBy(() -> relationshipService.addRelationship(alice.getId(), dto))
@@ -93,9 +99,9 @@ class RelationshipServiceIntegrationTest {
     void addRelationship_throws_409_when_circular_parent() {
         // alice PARENT_OF bob; now try bob PARENT_OF alice → must be rejected.
         relationshipService.addRelationship(alice.getId(),
-                new CreateRelationshipRequest(bob.getId(), RelationType.PARENT_OF, null, null, null));
+                new RelationshipUpsertRequest(bob.getId(), RelationType.PARENT_OF, null, null, null, null, null));
 
-        var reverse = new CreateRelationshipRequest(alice.getId(), RelationType.PARENT_OF, null, null, null);
+        var reverse = new RelationshipUpsertRequest(alice.getId(), RelationType.PARENT_OF, null, null, null, null, null);
         assertThatThrownBy(() -> relationshipService.addRelationship(bob.getId(), reverse))
                 .isInstanceOf(DomainException.class)
                 .extracting("code")
@@ -103,28 +109,58 @@ class RelationshipServiceIntegrationTest {
     }
 
     @Test
-    void deleteRelationship_throws_403_when_rel_belongs_to_different_person() {
+    void deleteRelationship_throws_404_when_rel_belongs_to_different_person() {
         RelationshipDTO created = relationshipService.addRelationship(alice.getId(),
-                new CreateRelationshipRequest(bob.getId(), RelationType.PARENT_OF, null, null, null));
+                new RelationshipUpsertRequest(bob.getId(), RelationType.PARENT_OF, null, null, null, null, null));
 
-        // Charlie is unrelated to this row.
+        // Charlie is unrelated to this row. Ownership mismatch is 404, not 403, so a
+        // curator cannot enumerate relationship ids belonging to people they can't see
+        // (anti-enumeration; aligned with the PUT endpoint — ADR-044).
         assertThatThrownBy(() -> relationshipService.deleteRelationship(charlie.getId(), created.id()))
                 .isInstanceOf(DomainException.class)
                 .extracting("code")
-                .isEqualTo(ErrorCode.FORBIDDEN);
+                .isEqualTo(ErrorCode.RELATIONSHIP_NOT_FOUND);
 
         // The row is still there.
         assertThat(relationshipRepository.findById(created.id())).isPresent();
     }
 
+    @Test
+    void updateRelationship_persists_new_type_dates_and_notes() {
+        RelationshipDTO created = relationshipService.addRelationship(alice.getId(),
+                new RelationshipUpsertRequest(bob.getId(), RelationType.FRIEND, null, null, null, null, null));
+
+        RelationshipDTO updated = relationshipService.updateRelationship(alice.getId(), created.id(),
+                new RelationshipUpsertRequest(bob.getId(), RelationType.SPOUSE_OF,
+                        LocalDate.of(1923, 5, 12), DatePrecision.DAY, null, null, "wedding day"));
+
+        assertThat(updated.id()).isEqualTo(created.id());
+        assertThat(updated.relationType()).isEqualTo(RelationType.SPOUSE_OF);
+        assertThat(updated.fromDate()).isEqualTo(LocalDate.of(1923, 5, 12));
+        assertThat(updated.fromDatePrecision()).isEqualTo(DatePrecision.DAY);
+        assertThat(updated.notes()).isEqualTo("wedding day");
+    }
+
+    @Test
+    void updateRelationship_throws_404_when_rel_belongs_to_different_person() {
+        RelationshipDTO created = relationshipService.addRelationship(alice.getId(),
+                new RelationshipUpsertRequest(bob.getId(), RelationType.PARENT_OF, null, null, null, null, null));
+
+        assertThatThrownBy(() -> relationshipService.updateRelationship(charlie.getId(), created.id(),
+                new RelationshipUpsertRequest(bob.getId(), RelationType.FRIEND, null, null, null, null, null)))
+                .isInstanceOf(DomainException.class)
+                .extracting("code")
+                .isEqualTo(ErrorCode.RELATIONSHIP_NOT_FOUND);
+    }
+
     @Test
     void addRelationship_throws_409_when_reverse_SPOUSE_OF_pair_already_exists() {
         // V55 enforces symmetric uniqueness for SPOUSE_OF. Inserting (alice, bob, SPOUSE_OF)
         // and then (bob, alice, SPOUSE_OF) must be rejected, just like reverse SIBLING_OF.
         relationshipService.addRelationship(alice.getId(),
-                new CreateRelationshipRequest(bob.getId(), RelationType.SPOUSE_OF, null, null, null));
+                new RelationshipUpsertRequest(bob.getId(), RelationType.SPOUSE_OF, null, null, null, null, null));
 
-        var reverse = new CreateRelationshipRequest(alice.getId(), RelationType.SPOUSE_OF, null, null, null);
+        var reverse = new RelationshipUpsertRequest(alice.getId(), RelationType.SPOUSE_OF, null, null, null, null, null);
         assertThatThrownBy(() -> relationshipService.addRelationship(bob.getId(), reverse))
                 .isInstanceOf(DomainException.class)
                 .extracting("code")
@@ -135,7 +171,7 @@ class RelationshipServiceIntegrationTest {
     void deleteRelationship_succeeds_for_symmetric_type_from_either_side() {
         // alice SPOUSE_OF bob. Bob deletes from his side.
         RelationshipDTO created = relationshipService.addRelationship(alice.getId(),
-                new CreateRelationshipRequest(bob.getId(), RelationType.SPOUSE_OF, null, null, null));
+                new RelationshipUpsertRequest(bob.getId(), RelationType.SPOUSE_OF, null, null, null, null, null));
 
         relationshipService.deleteRelationship(bob.getId(), created.id());
 
@@ -148,7 +184,7 @@ class RelationshipServiceIntegrationTest {
         // edges (PARENT_OF/SPOUSE_OF/SIBLING_OF). Reset charlie so the explicit
         // setFamilyMember(true) call below is the thing under test, not the auto-flip.
         relationshipService.addRelationship(alice.getId(),
-                new CreateRelationshipRequest(charlie.getId(), RelationType.PARENT_OF, null, null, null));
+                new RelationshipUpsertRequest(charlie.getId(), RelationType.PARENT_OF, null, null, null, null, null));
         relationshipService.setFamilyMember(charlie.getId(), false);
 
         NetworkDTO before = relationshipService.getFamilyNetwork();
@@ -165,7 +201,7 @@ class RelationshipServiceIntegrationTest {
     @Test
     void delete_person_cascades_to_relationships() {
         RelationshipDTO created = relationshipService.addRelationship(alice.getId(),
-                new CreateRelationshipRequest(bob.getId(), RelationType.PARENT_OF, null, null, null));
+                new RelationshipUpsertRequest(bob.getId(), RelationType.PARENT_OF, null, null, null, null, null));
         UUID relId = created.id();
         assertThat(relationshipRepository.findById(relId)).isPresent();
 

backend/src/test/java/org/raddatz/familienarchiv/person/relationship/RelationshipServiceTest.java

@@ -6,16 +6,18 @@ import org.junit.jupiter.api.extension.ExtendWith;
 import org.mockito.InjectMocks;
 import org.mockito.Mock;
 import org.mockito.junit.jupiter.MockitoExtension;
+import org.raddatz.familienarchiv.document.DatePrecision;
 import org.raddatz.familienarchiv.exception.DomainException;
 import org.raddatz.familienarchiv.exception.ErrorCode;
 import org.raddatz.familienarchiv.person.Person;
-import org.raddatz.familienarchiv.person.relationship.dto.CreateRelationshipRequest;
+import org.raddatz.familienarchiv.person.relationship.dto.RelationshipUpsertRequest;
 import org.raddatz.familienarchiv.person.PersonService;
 import org.springframework.dao.DataIntegrityViolationException;
 
 import org.raddatz.familienarchiv.person.relationship.dto.NetworkDTO;
 
 import java.time.Instant;
+import java.time.LocalDate;
 import java.util.List;
 import java.util.Optional;
 import java.util.UUID;
@@ -59,9 +61,9 @@ class RelationshipServiceTest {
         charlie = person("Charlie");
     }
 
-    // --- Nora blocker 1 ---
+    // --- Nora blocker 1 (anti-enumeration: ownership mismatch is 404, aligned with PUT) ---
     @Test
-    void deleteRelationship_throws_FORBIDDEN_when_rel_belongs_to_different_person() {
+    void deleteRelationship_throws_NOT_FOUND_when_rel_belongs_to_different_person() {
         UUID relId = UUID.randomUUID();
         PersonRelationship rel = parentOf(alice, bob, relId);
         when(relationshipRepository.findById(relId)).thenReturn(Optional.of(rel));
@@ -69,7 +71,7 @@ class RelationshipServiceTest {
         assertThatThrownBy(() -> service.deleteRelationship(charlie.getId(), relId))
                 .isInstanceOf(DomainException.class)
                 .extracting("code")
-                .isEqualTo(ErrorCode.FORBIDDEN);
+                .isEqualTo(ErrorCode.RELATIONSHIP_NOT_FOUND);
         verify(relationshipRepository, never()).delete(any());
     }
 
@@ -82,7 +84,7 @@ class RelationshipServiceTest {
         when(relationshipRepository.existsByPersonIdAndRelatedPersonIdAndRelationType(
                 alice.getId(), bob.getId(), RelationType.PARENT_OF)).thenReturn(true);
 
-        var dto = new CreateRelationshipRequest(alice.getId(), RelationType.PARENT_OF, null, null, null);
+        var dto = new RelationshipUpsertRequest(alice.getId(), RelationType.PARENT_OF, null, null, null, null, null);
         assertThatThrownBy(() -> service.addRelationship(bob.getId(), dto))
                 .isInstanceOf(DomainException.class)
                 .extracting("code")
@@ -98,7 +100,7 @@ class RelationshipServiceTest {
                 bob.getId(), alice.getId(), RelationType.PARENT_OF)).thenReturn(false);
         when(relationshipRepository.saveAndFlush(any())).thenThrow(new DataIntegrityViolationException("unique_rel"));
 
-        var dto = new CreateRelationshipRequest(bob.getId(), RelationType.PARENT_OF, null, null, null);
+        var dto = new RelationshipUpsertRequest(bob.getId(), RelationType.PARENT_OF, null, null, null, null, null);
         assertThatThrownBy(() -> service.addRelationship(alice.getId(), dto))
                 .isInstanceOf(DomainException.class)
                 .extracting("code")
@@ -107,7 +109,7 @@ class RelationshipServiceTest {
 
     @Test
     void addRelationship_throws_BAD_REQUEST_when_self_relationship() {
-        var dto = new CreateRelationshipRequest(alice.getId(), RelationType.FRIEND, null, null, null);
+        var dto = new RelationshipUpsertRequest(alice.getId(), RelationType.FRIEND, null, null, null, null, null);
         assertThatThrownBy(() -> service.addRelationship(alice.getId(), dto))
                 .isInstanceOf(DomainException.class)
                 .extracting("code")
@@ -116,14 +118,42 @@ class RelationshipServiceTest {
     }
 
     @Test
-    void addRelationship_throws_BAD_REQUEST_when_to_year_before_from_year() {
+    void addRelationship_throws_INVALID_RELATIONSHIP_DATES_when_toDate_before_fromDate() {
         when(personService.getById(alice.getId())).thenReturn(alice);
         when(personService.getById(bob.getId())).thenReturn(bob);
-        var dto = new CreateRelationshipRequest(bob.getId(), RelationType.FRIEND, 1950, 1940, null);
+        var dto = new RelationshipUpsertRequest(bob.getId(), RelationType.FRIEND,
+                LocalDate.of(1950, 1, 1), DatePrecision.YEAR,
+                LocalDate.of(1940, 1, 1), DatePrecision.YEAR, null);
         assertThatThrownBy(() -> service.addRelationship(alice.getId(), dto))
                 .isInstanceOf(DomainException.class)
                 .extracting("code")
-                .isEqualTo(ErrorCode.VALIDATION_ERROR);
+                .isEqualTo(ErrorCode.INVALID_RELATIONSHIP_DATES);
+        verify(relationshipRepository, never()).saveAndFlush(any());
+    }
+
+    @Test
+    void addRelationship_throws_INVALID_DATE_PRECISION_when_date_present_but_precision_unknown() {
+        when(personService.getById(alice.getId())).thenReturn(alice);
+        when(personService.getById(bob.getId())).thenReturn(bob);
+        var dto = new RelationshipUpsertRequest(bob.getId(), RelationType.FRIEND,
+                LocalDate.of(1950, 1, 1), DatePrecision.UNKNOWN, null, null, null);
+        assertThatThrownBy(() -> service.addRelationship(alice.getId(), dto))
+                .isInstanceOf(DomainException.class)
+                .extracting("code")
+                .isEqualTo(ErrorCode.INVALID_DATE_PRECISION);
+        verify(relationshipRepository, never()).saveAndFlush(any());
+    }
+
+    @Test
+    void addRelationship_throws_INVALID_DATE_PRECISION_when_precision_set_without_date() {
+        when(personService.getById(alice.getId())).thenReturn(alice);
+        when(personService.getById(bob.getId())).thenReturn(bob);
+        var dto = new RelationshipUpsertRequest(bob.getId(), RelationType.FRIEND,
+                null, DatePrecision.DAY, null, null, null);
+        assertThatThrownBy(() -> service.addRelationship(alice.getId(), dto))
+                .isInstanceOf(DomainException.class)
+                .extracting("code")
+                .isEqualTo(ErrorCode.INVALID_DATE_PRECISION);
         verify(relationshipRepository, never()).saveAndFlush(any());
     }
 
@@ -140,13 +170,16 @@ class RelationshipServiceTest {
             return r;
         });
 
-        var dto = new CreateRelationshipRequest(bob.getId(), RelationType.PARENT_OF, 1900, null, "first born");
+        var dto = new RelationshipUpsertRequest(bob.getId(), RelationType.PARENT_OF,
+                LocalDate.of(1900, 1, 1), DatePrecision.YEAR, null, null, "first born");
         var result = service.addRelationship(alice.getId(), dto);
 
         assertThat(result.personId()).isEqualTo(alice.getId());
         assertThat(result.relatedPersonId()).isEqualTo(bob.getId());
         assertThat(result.relationType()).isEqualTo(RelationType.PARENT_OF);
-        assertThat(result.fromYear()).isEqualTo(1900);
+        assertThat(result.fromDate()).isEqualTo(LocalDate.of(1900, 1, 1));
+        assertThat(result.fromDatePrecision()).isEqualTo(DatePrecision.YEAR);
+        assertThat(result.toDatePrecision()).isEqualTo(DatePrecision.UNKNOWN);
         assertThat(result.notes()).isEqualTo("first born");
     }
 
@@ -166,7 +199,7 @@ class RelationshipServiceTest {
             return r;
         });
 
-        var dto = new CreateRelationshipRequest(bob.getId(), RelationType.PARENT_OF, null, null, null);
+        var dto = new RelationshipUpsertRequest(bob.getId(), RelationType.PARENT_OF, null, null, null, null, null);
         service.addRelationship(alice.getId(), dto);
 
         verify(personService).setFamilyMember(alice.getId(), true);
@@ -187,7 +220,7 @@ class RelationshipServiceTest {
             return r;
         });
 
-        var dto = new CreateRelationshipRequest(bob.getId(), RelationType.FRIEND, null, null, null);
+        var dto = new RelationshipUpsertRequest(bob.getId(), RelationType.FRIEND, null, null, null, null, null);
         service.addRelationship(alice.getId(), dto);
 
         verify(personService, never()).setFamilyMember(eq(alice.getId()), anyBoolean());
@@ -216,6 +249,131 @@ class RelationshipServiceTest {
                 .isEqualTo(ErrorCode.RELATIONSHIP_NOT_FOUND);
     }
 
+    // --- updateRelationship (REQ-004/006/007/008/009/010/013) ---
+
+    @Test
+    void updateRelationship_throws_NOT_FOUND_when_relId_unknown() {
+        UUID relId = UUID.randomUUID();
+        when(relationshipRepository.findById(relId)).thenReturn(Optional.empty());
+
+        var dto = new RelationshipUpsertRequest(bob.getId(), RelationType.FRIEND, null, null, null, null, null);
+        assertThatThrownBy(() -> service.updateRelationship(alice.getId(), relId, dto))
+                .isInstanceOf(DomainException.class)
+                .extracting("code")
+                .isEqualTo(ErrorCode.RELATIONSHIP_NOT_FOUND);
+        verify(relationshipRepository, never()).saveAndFlush(any());
+    }
+
+    @Test
+    void updateRelationship_throws_NOT_FOUND_when_rel_belongs_to_different_person() {
+        UUID relId = UUID.randomUUID();
+        PersonRelationship rel = parentOf(alice, bob, relId);
+        when(relationshipRepository.findById(relId)).thenReturn(Optional.of(rel));
+
+        var dto = new RelationshipUpsertRequest(bob.getId(), RelationType.FRIEND, null, null, null, null, null);
+        assertThatThrownBy(() -> service.updateRelationship(charlie.getId(), relId, dto))
+                .isInstanceOf(DomainException.class)
+                .extracting("code")
+                .isEqualTo(ErrorCode.RELATIONSHIP_NOT_FOUND);
+        verify(relationshipRepository, never()).saveAndFlush(any());
+    }
+
+    @Test
+    void updateRelationship_throws_VALIDATION_ERROR_on_self_relation() {
+        UUID relId = UUID.randomUUID();
+        PersonRelationship rel = relOf(alice, bob, RelationType.FRIEND, relId);
+        when(relationshipRepository.findById(relId)).thenReturn(Optional.of(rel));
+
+        var dto = new RelationshipUpsertRequest(alice.getId(), RelationType.FRIEND, null, null, null, null, null);
+        assertThatThrownBy(() -> service.updateRelationship(alice.getId(), relId, dto))
+                .isInstanceOf(DomainException.class)
+                .extracting("code")
+                .isEqualTo(ErrorCode.VALIDATION_ERROR);
+        verify(relationshipRepository, never()).saveAndFlush(any());
+    }
+
+    @Test
+    void updateRelationship_throws_INVALID_RELATIONSHIP_DATES_when_toDate_before_fromDate() {
+        UUID relId = UUID.randomUUID();
+        PersonRelationship rel = relOf(alice, bob, RelationType.FRIEND, relId);
+        when(relationshipRepository.findById(relId)).thenReturn(Optional.of(rel));
+
+        var dto = new RelationshipUpsertRequest(bob.getId(), RelationType.FRIEND,
+                LocalDate.of(1950, 1, 1), DatePrecision.YEAR,
+                LocalDate.of(1940, 1, 1), DatePrecision.YEAR, null);
+        assertThatThrownBy(() -> service.updateRelationship(alice.getId(), relId, dto))
+                .isInstanceOf(DomainException.class)
+                .extracting("code")
+                .isEqualTo(ErrorCode.INVALID_RELATIONSHIP_DATES);
+        verify(relationshipRepository, never()).saveAndFlush(any());
+    }
+
+    @Test
+    void updateRelationship_throws_CIRCULAR_when_reverse_PARENT_OF_exists() {
+        UUID relId = UUID.randomUUID();
+        PersonRelationship rel = relOf(alice, bob, RelationType.FRIEND, relId);
+        when(relationshipRepository.findById(relId)).thenReturn(Optional.of(rel));
+        when(personService.getById(bob.getId())).thenReturn(bob);
+        when(relationshipRepository.existsByPersonIdAndRelatedPersonIdAndRelationType(
+                bob.getId(), alice.getId(), RelationType.PARENT_OF)).thenReturn(true);
+
+        var dto = new RelationshipUpsertRequest(bob.getId(), RelationType.PARENT_OF, null, null, null, null, null);
+        assertThatThrownBy(() -> service.updateRelationship(alice.getId(), relId, dto))
+                .isInstanceOf(DomainException.class)
+                .extracting("code")
+                .isEqualTo(ErrorCode.CIRCULAR_RELATIONSHIP);
+        verify(relationshipRepository, never()).saveAndFlush(any());
+    }
+
+    @Test
+    void updateRelationship_throws_DUPLICATE_when_db_constraint_violated() {
+        UUID relId = UUID.randomUUID();
+        PersonRelationship rel = relOf(alice, bob, RelationType.FRIEND, relId);
+        when(relationshipRepository.findById(relId)).thenReturn(Optional.of(rel));
+        when(personService.getById(bob.getId())).thenReturn(bob);
+        when(relationshipRepository.saveAndFlush(any())).thenThrow(new DataIntegrityViolationException("unique_rel"));
+
+        var dto = new RelationshipUpsertRequest(bob.getId(), RelationType.SPOUSE_OF, null, null, null, null, null);
+        assertThatThrownBy(() -> service.updateRelationship(alice.getId(), relId, dto))
+                .isInstanceOf(DomainException.class)
+                .extracting("code")
+                .isEqualTo(ErrorCode.DUPLICATE_RELATIONSHIP);
+    }
+
+    @Test
+    void updateRelationship_updates_fields_and_returns_dto() {
+        UUID relId = UUID.randomUUID();
+        PersonRelationship rel = relOf(alice, bob, RelationType.FRIEND, relId);
+        when(relationshipRepository.findById(relId)).thenReturn(Optional.of(rel));
+        when(personService.getById(bob.getId())).thenReturn(bob);
+        when(relationshipRepository.saveAndFlush(any())).thenAnswer(inv -> inv.getArgument(0));
+
+        var dto = new RelationshipUpsertRequest(bob.getId(), RelationType.SPOUSE_OF,
+                LocalDate.of(1923, 5, 12), DatePrecision.DAY, null, null, "wedding day");
+        var result = service.updateRelationship(alice.getId(), relId, dto);
+
+        assertThat(result.relationType()).isEqualTo(RelationType.SPOUSE_OF);
+        assertThat(result.fromDate()).isEqualTo(LocalDate.of(1923, 5, 12));
+        assertThat(result.fromDatePrecision()).isEqualTo(DatePrecision.DAY);
+        assertThat(result.toDatePrecision()).isEqualTo(DatePrecision.UNKNOWN);
+        assertThat(result.notes()).isEqualTo("wedding day");
+    }
+
+    @Test
+    void updateRelationship_marks_both_endpoints_family_when_updated_to_family_type() {
+        UUID relId = UUID.randomUUID();
+        PersonRelationship rel = relOf(alice, bob, RelationType.FRIEND, relId);
+        when(relationshipRepository.findById(relId)).thenReturn(Optional.of(rel));
+        when(personService.getById(bob.getId())).thenReturn(bob);
+        when(relationshipRepository.saveAndFlush(any())).thenAnswer(inv -> inv.getArgument(0));
+
+        var dto = new RelationshipUpsertRequest(bob.getId(), RelationType.SIBLING_OF, null, null, null, null, null);
+        service.updateRelationship(alice.getId(), relId, dto);
+
+        verify(personService).setFamilyMember(alice.getId(), true);
+        verify(personService).setFamilyMember(bob.getId(), true);
+    }
+
     @Test
     void getFamilyNetwork_excludes_edges_where_one_endpoint_is_not_a_family_member() {
         // alice and bob are family members; charlie is NOT (not in findAllFamilyMembers result).
@@ -260,11 +418,15 @@ class RelationshipServiceTest {
     }
 
     private static PersonRelationship parentOf(Person parent, Person child, UUID id) {
+        return relOf(parent, child, RelationType.PARENT_OF, id);
+    }
+
+    private static PersonRelationship relOf(Person subject, Person object, RelationType type, UUID id) {
         return PersonRelationship.builder()
                 .id(id)
-                .person(parent)
+                .person(subject)
-                .relatedPerson(child)
+                .relatedPerson(object)
-                .relationType(RelationType.PARENT_OF)
+                .relationType(type)
                 .createdAt(Instant.now())
                 .build();
     }

backend/src/test/java/org/raddatz/familienarchiv/timeline/DerivedEventsAssemblyTest.java

@@ -81,12 +81,19 @@ class DerivedEventsAssemblyTest {
     }
 
     private PersonRelationship makeSpouseEdge(Person a, Person b, Integer fromYear) {
+        return makeSpouseEdgeWithDate(a, b,
+                fromYear != null ? LocalDate.of(fromYear, 1, 1) : null,
+                fromYear != null ? DatePrecision.YEAR : DatePrecision.UNKNOWN);
+    }
+
+    private PersonRelationship makeSpouseEdgeWithDate(Person a, Person b, LocalDate fromDate, DatePrecision precision) {
         return PersonRelationship.builder()
                 .id(UUID.randomUUID())
                 .person(a)
                 .relatedPerson(b)
                 .relationType(RelationType.SPOUSE_OF)
-                .fromYear(fromYear)
+                .fromDate(fromDate)
+                .fromDatePrecision(precision)
                 .build();
     }
 
@@ -223,6 +230,24 @@ class DerivedEventsAssemblyTest {
         assertThat(heirat.precision()).isEqualTo(DatePrecision.UNKNOWN);
     }
 
+    // --- REQ-017 (#837): derived Heirat sources SPOUSE_OF.fromDate at its stored precision ---
+
+    @Test
+    void should_emit_day_precision_heirat_from_spouse_fromDate() {
+        Person anna = makePerson(null, DatePrecision.UNKNOWN);
+        Person hans = makePersonWithDeath(null, DatePrecision.UNKNOWN);
+        PersonRelationship edge = makeSpouseEdgeWithDate(anna, hans, LocalDate.of(1923, 5, 12), DatePrecision.DAY);
+        when(personService.findAllFamilyMembers()).thenReturn(List.of(anna, hans));
+        when(relationshipService.findAllSpouseEdges()).thenReturn(List.of(edge));
+
+        TimelineEntryDTO heirat = service.assembleDerivedEvents().stream()
+                .filter(e -> e.derivedType() == DerivedEventType.MARRIAGE)
+                .findFirst().orElseThrow();
+
+        assertThat(heirat.eventDate()).isEqualTo(LocalDate.of(1923, 5, 12));
+        assertThat(heirat.precision()).isEqualTo(DatePrecision.DAY);
+    }
+
     // --- REQ-007: exactly one Heirat per SPOUSE_OF edge (dedup) ---
 
     @Test

backend/src/test/java/org/raddatz/familienarchiv/timeline/TimelineServiceTest.java

@@ -69,10 +69,10 @@ class TimelineServiceTest {
         UUID id2 = UUID.fromString("00000000-0000-0000-0000-000000000002");
         var e1 = new TimelineEntryDTO(Kind.LETTER, DatePrecision.DAY, false, "", "",
                 LocalDate.of(1914, 7, 28), null, "Same Title", null, null, id1, List.of(), null,
-                null, null, null);
+                null, null, null, null);
         var e2 = new TimelineEntryDTO(Kind.LETTER, DatePrecision.DAY, false, "", "",
                 LocalDate.of(1914, 7, 28), null, "Same Title", null, null, id2, List.of(), null,
-                null, null, null);
+                null, null, null, null);
 
         var sorted = List.of(e2, e1).stream()
                 .sorted(TimelineService.WITHIN_BAND_ORDER)
@@ -511,6 +511,44 @@ class TimelineServiceTest {
         verify(tagService, times(1)).resolveRootTags(anyList());
     }
 
+    // ─── letter→event link (#827, REQ-005/006) ───────────────────────────────
+
+    @Test
+    void letter_in_a_curated_events_documents_carries_that_events_id() {
+        // REQ-005: linkedEventId = the curated event whose documents set contains the letter.
+        Document letterDoc = docWithDate(LocalDate.of(1915, 5, 1), DatePrecision.MONTH);
+        UUID eventId = UUID.randomUUID();
+        TimelineEvent event = TimelineEvent.builder().id(eventId)
+                .title("Briefe von der Front").type(EventType.PERSONAL)
+                .documents(new HashSet<>(Set.of(letterDoc)))
+                .build(); // no eventDate → event lands undated, leaving the year band to the letter
+        when(eventRepository.findAll()).thenReturn(List.of(event));
+        when(timelineEventService.assembleDerivedEvents()).thenReturn(List.of());
+        when(documentService.getAllForTimeline()).thenReturn(List.of(letterDoc));
+
+        TimelineEntryDTO entry = onlyLetterEntry(timelineService.assemble(noFilters()));
+
+        assertThat(entry.linkedEventId()).isEqualTo(eventId);
+    }
+
+    @Test
+    void letter_in_no_curated_event_has_null_linkedEventId() {
+        // REQ-006: a letter referenced by no curated event → linkedEventId null (frontend falls
+        // back to the per-year "Weitere Briefe" bucket).
+        Document letterDoc = docWithDate(LocalDate.of(1915, 5, 1), DatePrecision.MONTH);
+        TimelineEvent event = TimelineEvent.builder().id(UUID.randomUUID())
+                .title("Anderes Ereignis").type(EventType.PERSONAL)
+                .documents(new HashSet<>(Set.of(Document.builder().id(UUID.randomUUID()).build())))
+                .build();
+        when(eventRepository.findAll()).thenReturn(List.of(event));
+        when(timelineEventService.assembleDerivedEvents()).thenReturn(List.of());
+        when(documentService.getAllForTimeline()).thenReturn(List.of(letterDoc));
+
+        TimelineEntryDTO entry = onlyLetterEntry(timelineService.assemble(noFilters()));
+
+        assertThat(entry.linkedEventId()).isNull();
+    }
+
     private static TimelineEntryDTO onlyLetterEntry(TimelineDTO result) {
         assertThat(result.years()).hasSize(1);
         return result.years().get(0).entries().get(0);
@@ -523,7 +561,7 @@ class TimelineServiceTest {
     private static TimelineEntryDTO letter(LocalDate date, DatePrecision precision, String title) {
         return new TimelineEntryDTO(Kind.LETTER, precision, false, "", "",
                 date, null, title, null, null, UUID.randomUUID(), List.of(), null,
-                null, null, null);
+                null, null, null, null);
     }
 
     private static Document docWithDate(LocalDate date, DatePrecision precision) {

docs/DEPLOYMENT.md

@@ -538,6 +538,29 @@ pg_restore -t persons -d ${POSTGRES_DB} backup-YYYYMMDD.dump
 
 (For a plain-SQL dump, extract the persons COPY block instead of replaying the full file.)
 
+### Deploy note — V78 (person_relationships from/to → date + precision, #837)
+
+V78 drops `person_relationships.from_year`/`to_year` after backfilling the new
+`from_date`/`to_date` + precision columns — a **one-way migration** (Flyway cannot roll
+it back). Like V76 it runs its pre-check + DDL in one atomic Flyway transaction and
+needs **no maintenance window** (single-writer archive, no concurrent importers).
+
+It is, however, **not rolling-deploy-safe**: the previously-running JAR still maps the
+`from_year`/`to_year` columns, so it would error against the migrated schema. Deploy in
+this order (the default stop-then-start, single-instance deploy already satisfies it):
+
+1. Take a manual `pg_dump` (see above) and confirm it completed.
+2. **Stop the old JAR**, then **start the new JAR** — Flyway V78 runs first thing on the
+   new JAR's startup, before any request is served. Never run the old and new JARs
+   concurrently across this migration.
+
+If post-deploy data issues are found, restore **only the person_relationships table**
+from the pre-migration dump:
+
+```bash
+pg_restore -t person_relationships -d ${POSTGRES_DB} backup-YYYYMMDD.dump
+```
+
 ### Rollback
 
 Each release tag corresponds to a docker image tag on the host daemon (built via DooD; no registry). Rolling back to a previous tag is one command:

docs/adr/044-relationship-dates-localdate-precision.md

@@ -0,0 +1,91 @@
+# ADR-044 — Relationship dates become LocalDate + DatePrecision; relationships become editable
+
+**Status:** Accepted
+**Date:** 2026-06-14
+**Issue:** #837 (Zeitstrahl milestone; deferred follow-up to #773 / ADR-039)
+
+## Context
+
+`PersonRelationship` stored its span as `Integer fromYear`/`toYear`. A wedding could
+never be more precise than `1923`, while `Person` (ADR-039), `Document`, and
+`TimelineEvent` already carry full `DatePrecision`. Relationships also supported only
+create + delete: fixing a wrong type, a wrong person, or adding a date learned later
+meant deleting and re-creating the edge — losing `createdAt`. A `notes` column existed
+that no form set and nothing displayed.
+
+V78 replaces the two integer columns with `from_date`/`to_date` (`DATE`, nullable) plus
+`from_date_precision`/`to_date_precision` (`VARCHAR(16) NOT NULL DEFAULT 'UNKNOWN'`),
+backfilling existing years as `YYYY-01-01` at `YEAR` precision — exactly the V76 / ADR-039
+pattern applied to the relationship edge. A new `PUT /api/persons/{id}/relationships/{relId}`
+makes relationships editable, and `notes` is activated end to end.
+
+## Decisions
+
+### 1. Mirror ADR-039 verbatim for the relationship edge
+
+`DatePrecision` is imported cross-domain from `document/` (ADR-039 §1 — value-type
+sharing, not a layering breach). The precision columns are NOT NULL default `UNKNOWN`,
+guarded by five named CHECK constraints (`chk_relationship_from_coherence`,
+`chk_relationship_to_coherence`, `chk_relationship_date_order`,
+`chk_relationship_{from,to}_precision_values`). `RelationshipService.validateRelationshipDates`
+enforces the same rules first, so the user gets a structured 400
+(`INVALID_DATE_PRECISION` for coherence, the new `INVALID_RELATIONSHIP_DATES` for a
+`toDate < fromDate` order violation) instead of a constraint-violation 500. The form
+offers only **DAY / MONTH / YEAR**; storage still accepts all seven values, and a
+stored non-offered precision seeds the edit select as `YEAR` (ADR-039 §2).
+
+### 2. Update re-runs every create invariant
+
+An edit can violate the same invariants as a create, so `updateRelationship` re-runs
+all of them: self-relation (`VALIDATION_ERROR`), date coherence + order, reverse
+`PARENT_OF` (`CIRCULAR_RELATIONSHIP`), and the `(person, relatedPerson, type)` unique
+constraint via `saveAndFlush` (`DUPLICATE_RELATIONSHIP`). Editing into a family type
+flags both endpoints as family members (additive; never auto-unflags). The directed
+orientation is preserved per viewpoint — whichever endpoint `{personId}` already holds
+on the row stays put — so a `PARENT_OF` edge remains parent→child whether edited from
+either person's page.
+
+### 3. No optimistic locking (`@Version`)
+
+`PersonRelationship` gains no `@Version`; the edit is last-write-wins, matching the
+person edit form. This is a single-writer family archive, and it avoids the managed-
+`setVersion` pitfall (a `setVersion` on a managed entity is silently ignored by
+Hibernate — see the integration-test note in #496-era work). If concurrent curation
+ever becomes real, add `@Version` plus an explicit client-version compare then.
+
+### 4. IDOR / anti-enumeration: ownership mismatch is 404, for PUT **and** DELETE
+
+A `{relId}` that does not belong to `{personId}` returns 404 `RELATIONSHIP_NOT_FOUND`
+(a shared `loadOwnedRelationship` helper), so a curator cannot probe relationship ids
+belonging to people they cannot see. This **aligns `deleteRelationship`** from its
+former 403 to 404 in the same change, so the two mutating endpoints behave identically
+on the same mismatch.
+
+### 5. Derived marriage events gain precision for free
+
+`TimelineEventService.buildMarriageEvents` now sources the Heirat date from the
+`SPOUSE_OF` row's `from_date` + `from_date_precision` (previously
+`LocalDate.of(fromYear, 1, 1)` at hard-coded `YEAR`). A DAY-precision wedding now
+surfaces the exact day on the Zeitstrahl. `RelationshipInferenceService` is unchanged
+— it is time-ignorant and never read the year fields.
+
+### 6. `relationshipDates.ts` lives in `$lib/person/`, no new boundary
+
+`formatRelationshipDateRange` mirrors `personLifeDates.ts` and delegates entirely to the
+already-tested `formatDocumentDate` (zero new precision logic). It sits in `$lib/person/`
+next to `personLifeDates.ts`; its only cross-domain import is `formatDocumentDate` from
+`$lib/shared/utils/`, which the existing `person → shared` rule in `eslint.config.js`
+already permits — **no new eslint boundary rule is added**.
+
+## Consequences
+
+- V78 is one-way (columns dropped) and is **not** rolling-deploy-safe — the running JAR
+  maps `from_year` until redeploy. Deploy order: **stop old JAR → run Flyway V78 →
+  start new JAR**. Rollback = targeted `pg_restore -t person_relationships` from the
+  pre-deploy dump (see `docs/DEPLOYMENT.md` §8). No maintenance window needed
+  (single-writer archive).
+- Relationships are fully editable (type, related person, dates, notes) and the read
+  view shows the date range + notes.
+- `RelationshipDTO` drops `fromYear`/`toYear` for `fromDate`/`fromDatePrecision`/
+  `toDate`/`toDatePrecision`; the `personBirthYear`/`relatedPersonBirthYear` derived
+  fields are unaffected (ADR-039 §3).

docs/adr/045-timeline-client-side-regroup.md

@@ -0,0 +1,78 @@
+# ADR-045 — The /zeitstrahl Ereignis/Thema regroup is client-side, over a computed letter→event link
+
+**Status:** Accepted
+**Date:** 2026-06-15
+**Issue:** #827 (Zeitstrahl milestone; deferred follow-up to #779, builds on #835/PR #838 and #780)
+
+## Context
+
+#779 shipped `/zeitstrahl` in **Datum** mode only and deferred the Concept-A
+**Datum · Ereignis · Thema** segmented control, because the other two modes need data the
+`TimelineEntryDTO` did not carry: a letter's curated-event association (Ereignis) and a letter's
+primary root tag + colour (Thema). #835 (merged in PR #838) added the Thema fields
+(`rootTagId`/`rootTagName`/`rootTagColor`) and the batched `TimelineService → TagService`
+resolver. Meanwhile #780 added the **layer filter** — `/zeitstrahl/+page.svelte` owns
+`personalOn`/`historicalOn`/`lettersOn` `$state` and renders `TimelineView` over a client-side
+`filterTimeline(data.timeline, …)` view.
+
+This ADR records the three forks specific to **#827** (the Thema enrichment + the
+`TimelineService → TagService` edge are #835's scope, not this one).
+
+## Decisions
+
+### 1. Grouping is a client-side presentation transform — no `grouping=` query param
+
+`GET /api/timeline` already returns the whole timeline in one payload. Regrouping the loose
+letters is an in-memory transform in `lib/timeline/timelineGrouping.ts` (`bucketLetters`,
+`buildEventLookup`, `hasLooseLetters`), driven by a `groupingMode` `$state` in `+page.svelte`.
+A server-side `grouping=DATE|EVENT|TOPIC` parameter was rejected: it would add lasting API
+surface and a bucket query for zero benefit on an already-loaded payload, and switching modes
+must issue **zero** extra fetches (REQ-002). The blast radius stays inside the read view.
+
+### 2. The letter→event link is computed, reusing `timeline_event_documents` — no new column
+
+A letter clusters under a curated event iff that event's `documents` set (ADR-040;
+`@ManyToMany @BatchSize(50)` over join table `timeline_event_documents`) contains the letter's
+document. `TimelineService.assemble` resolves this in **one batched membership pass** —
+`resolveLetterEventLinks` builds a single `docId → eventId` map over the already-loaded events
+(no per-letter query), reusing the same `eventRepository.findAll()` it already iterates for the
+event entries. The result is exposed as one nullable DTO field, `linkedEventId`. A new persisted
+FK on the document/letter row was rejected: it duplicates an existing capability and opens a
+mutating write path + Flyway migration for no gain. **No new column, no migration, no new
+cross-domain edge** (the field derives from data `TimelineService` already loads). `linkedEventId`
+is deliberately **not** `@Schema(requiredMode = REQUIRED)` — it is null for non-letter entries and
+for letters under no curated event — so the generated TypeScript type stays optional.
+
+### 3. Grouping composes with the #780 layer filter as **filter-then-group**
+
+The pipeline is `data.timeline → filterTimeline() (#780) → groupingMode transform → TimelineView`.
+The grouping `$state` lives in `+page.svelte` beside the filter `$state`, and the regroup runs over
+the layer-**filtered** view, never the raw `data.timeline`. Grouping the raw timeline and filtering
+afterward was rejected: the counts and buckets would disagree with the layer toggles, re-opening
+the #780 count-mismatch the page already closed. Two consequences fall out of filter-then-group:
+
+- **Letters layer off → the grouping control disables, kept in place (REQ-018).** With no loose
+  letters in the filtered view there is nothing to regroup; the control renders `aria-disabled`
+  (no header reflow), keeps its selected mode, and announces a screen-reader reason.
+- **A letter whose only linking event was filtered out falls back to "Weitere Briefe" (REQ-019).**
+  `buildEventLookup` is built from the events present in the _filtered_ view, so Ereignis clusters
+  only under events that survived the filter; everything else lands in the per-year fallback bucket.
+
+The control is a `role="radiogroup"` (single-select), deliberately distinct from #780's
+`aria-pressed` toggle filter, stacked above the filter trigger so the two read as one control
+cluster — the top-right corner stays the #842 add-event CTA.
+
+## Consequences
+
+- One nullable field (`linkedEventId`) is added to `TimelineEntryDTO` (17 components); the
+  regenerated `frontend/src/lib/generated/api.ts` is committed in the same PR. No table, column,
+  Flyway migration, endpoint, `ErrorCode`, or `Permission` changes.
+- The regroup is pure and fully unit-tested independently of the components; `TimelineView`/
+  `YearBand` render the axis-fixed event layer identically across all three modes (REQ-001) and
+  only swap the loose-letter rendering for per-year `LetterBucket`s off Datum.
+- The new Thema bucket-header chip (`BucketHeaderChip`) is a filled variant tinted from
+  `rootTagColor`; the shipped neutral per-letter `TagChip` (#838) is reused as-is and suppressed
+  inside its own bucket (REQ-017). All `lib/timeline` components keep the `{...}`-escaping
+  guarantee — a grep gate forbids `{@html}` (REQ-009).
+- Read-only feature: no new authn/authz surface beyond the existing `READ_ALL` on
+  `GET /api/timeline`.

docs/architecture/db/db-orm.puml

@@ -1,6 +1,6 @@
 @startuml db-orm
-' Schema source: Flyway V1–V77 (excl. V37, V43 — intentionally removed)
+' Schema source: Flyway V1–V78 (excl. V37, V43 — intentionally removed)
-' Schema as of:  V77 (2026-06-12)
+' Schema as of:  V78 (2026-06-14)
 ' ⚠ This is a versioned snapshot. Update when the schema changes significantly.
 
 hide circle
@@ -211,8 +211,10 @@ package "Persons" {
     person_id : UUID <<FK>>
     related_person_id : UUID <<FK>>
     relation_type : VARCHAR(30) NOT NULL
-    from_year : INTEGER
+    from_date : DATE
-    to_year : INTEGER
+    from_date_precision : VARCHAR(16) NOT NULL DEFAULT 'UNKNOWN'
+    to_date : DATE
+    to_date_precision : VARCHAR(16) NOT NULL DEFAULT 'UNKNOWN'
     notes : VARCHAR(2000)
     created_at : TIMESTAMPTZ NOT NULL
   }

docs/architecture/db/db-relationships.puml

@@ -7,6 +7,8 @@
 ' Note: V76 swaps persons.birth_year/death_year for birth_date/death_date +
 ' precision columns; columns only, no new FK relationships, diagram unchanged.
 ' Note: V77 adds the timeline_events table + two join tables (Timeline package below).
+' Note: V78 swaps person_relationships.from_year/to_year for from_date/to_date +
+' precision columns; columns only, no new FK relationships, diagram unchanged.
 
 hide circle
 skinparam linetype ortho

docs/superpowers/plans/2026-06-15-zeitstrahl-grouped-card-layout.md

@@ -0,0 +1,374 @@
+# Zeitstrahl grouped-view contained-card layout — Implementation Plan
+
+> **For agentic workers:** REQUIRED SUB-SKILL: Use superpowers:subagent-driven-development (recommended) or superpowers:executing-plans to implement this plan task-by-task. Steps use checkbox (`- [ ]`) syntax for tracking.
+
+**Goal:** Replace the grouped-view's full-width bucket blocks with self-contained cards — a cluster (event or root tag) becomes one bordered card whose header is the event/tag and whose body shows the first 5 letters with a show-more toggle; the leftover bin collapses to a count-only drawer; a same-year curated event renders *as* its card header (no duplicate pill).
+
+**Architecture:** Frontend-only, on branch `feat/issue-827-zeitstrahl-grouping` (worktree `.worktrees/issue-827-zeitstrahl-grouping`). Evolve `LetterBucket.svelte` into the contained card (preview cap + show-more + collapsed drawer + card chrome + optional event header) and rewire `YearBand.svelte`'s Ereignis branch so a same-year curated event becomes the card header instead of a separate pill. Datum mode is untouched. Design doc: `docs/superpowers/specs/2026-06-15-zeitstrahl-grouped-view-layout-design.md`.
+
+**Tech Stack:** Svelte 5 (runes), Tailwind 4, Paraglide i18n, Vitest browser mode (`--project=client` for `*.svelte.spec.ts`, `--project=server` for plain `*.spec.ts`).
+
+**Conventions (read before starting):**
+- Red→green TDD, one logical change per commit, `Refs #827` on the last body line.
+- Run only the specific spec file(s) — never the full suite. Client: `npx vitest run <file> --project=client`; server: `... --project=server`.
+- Before each commit: `npx prettier --write <changed files>`, then `git add <files>` + `git diff --cached --stat` to verify the staged set, then commit (the pre-commit hook runs `prettier --check` + `eslint`).
+- **No `new Set()`/`new Map()` inside a `.svelte` file** — `svelte/prefer-svelte-reactivity` errors even on transient locals. Use plain arrays (`find`/`some`/`filter`) inside `$derived`. (Pure `.ts` modules are fine.)
+- Prettier rewrites `class:foo` shorthand to `class:foo={foo}` — expect that.
+- Factories in `frontend/src/lib/timeline/test-factories.ts`: `makeEntry`, `makeYear`, `makeTimelineDTO`.
+
+---
+
+## File Structure
+
+- `frontend/src/lib/timeline/timelineGrouping.ts` — add `CLUSTER_PREVIEW = 5`; remove `BUCKET_DENSE_THRESHOLD`/`isBucketDense` (no longer used). Keep `bucketLetters`, `buildEventLookup`, `hasLooseLetters`, `tagColorVar`.
+- `frontend/src/lib/timeline/LetterBucket.svelte` — the contained card: card chrome + colour rail + header variants (tag chip / event-header / cross-year text label / drawer label) + body (first-5 preview, show-more toggle, drawer collapsed-by-default). Drop the `YearLetterStrip` branch.
+- `frontend/src/lib/timeline/YearBand.svelte` — Ereignis branch: a same-year curated event renders as a `LetterBucket` card with `event={entry}` (no separate pill); letterless/derived/world events stay plain; cross-year clusters + the fallback drawer render after the axis entries.
+- `frontend/messages/{de,en,es}.json` — two new keys: `timeline_bucket_show_more` (`{count}`), `timeline_bucket_show_less`.
+- Specs: `LetterBucket.svelte.spec.ts`, `YearBand.svelte.spec.ts`, `messages.spec.ts` (extend), plus the route spec stays green.
+- `.specify/rtm.md` — update REQ-014/REQ-020 rows.
+
+---
+
+## Task 1: Preview cap + show-more toggle (drop the sparkline)
+
+**Files:**
+- Modify: `frontend/src/lib/timeline/timelineGrouping.ts`
+- Modify: `frontend/src/lib/timeline/LetterBucket.svelte`
+- Test: `frontend/src/lib/timeline/LetterBucket.svelte.spec.ts`
+
+- [ ] **Step 1: Add the i18n keys** in all three locales (so the toggle has a label).
+
+`frontend/messages/de.json` (next to the existing `timeline_bucket_*` keys):
+```json
+"timeline_bucket_show_more": "+ {count} weitere Briefe anzeigen",
+"timeline_bucket_show_less": "Weniger anzeigen",
+```
+`en.json`: `"+ {count} more letters"`, `"Show fewer"`. `es.json`: `"+ {count} cartas más"`, `"Mostrar menos"`.
+Run `npx @inlang/paraglide-js compile --project ./project.inlang --outdir ./src/lib/paraglide` (from `frontend/`) or let the dev/test build compile them.
+
+- [ ] **Step 2: Write the failing tests** in `LetterBucket.svelte.spec.ts` (replace the `manyLetters`-based density tests from PR #847 — the sparkline is going away).
+
+```ts
+const manyLetters = (n: number) =>
+	Array.from({ length: n }, (_, i) => makeEntry({ documentId: `d${i}`, eventDate: `1916-0${(i % 9) + 1}-01` }));
+
+describe('LetterBucket — preview cap + show-more (#827 redesign)', () => {
+	it('shows only the first 5 letters with a show-more toggle when the cluster is larger', () => {
+		const bucket: Bucket = { key: 'tag:t1', kind: 'tag', title: 'Krieg', color: 'sienna', letters: manyLetters(8) };
+		render(LetterBucket, { bucket, mode: 'thema', year: 1916 });
+		expect(document.querySelectorAll('a.lcard')).toHaveLength(5);
+		expect(document.querySelector('[data-testid="bucket-show-more"]')).not.toBeNull();
+		expect(document.querySelector('[data-testid="strip-expand"]')).toBeNull(); // sparkline gone
+	});
+
+	it('expands to all letters and collapses back on toggle', async () => {
+		const bucket: Bucket = { key: 'tag:t1', kind: 'tag', title: 'Krieg', color: 'sienna', letters: manyLetters(8) };
+		render(LetterBucket, { bucket, mode: 'thema', year: 1916 });
+		(document.querySelector('[data-testid="bucket-show-more"]') as HTMLButtonElement).click();
+		await tick();
+		expect(document.querySelectorAll('a.lcard')).toHaveLength(8);
+		(document.querySelector('[data-testid="bucket-show-more"]') as HTMLButtonElement).click();
+		await tick();
+		expect(document.querySelectorAll('a.lcard')).toHaveLength(5);
+	});
+
+	it('shows all letters and no toggle for a small cluster (<= 5)', () => {
+		const bucket: Bucket = { key: 'tag:t1', kind: 'tag', title: 'Tod', color: null, letters: manyLetters(3) };
+		render(LetterBucket, { bucket, mode: 'thema', year: 1916 });
+		expect(document.querySelectorAll('a.lcard')).toHaveLength(3);
+		expect(document.querySelector('[data-testid="bucket-show-more"]')).toBeNull();
+	});
+});
+```
+Add `import { tick } from 'svelte';` at the top of the spec if absent.
+
+- [ ] **Step 3: Run the tests — verify they fail.** `npx vitest run src/lib/timeline/LetterBucket.svelte.spec.ts --project=client` → FAIL (still rendering the strip / all cards).
+
+- [ ] **Step 4: Implement.** In `timelineGrouping.ts` remove `BUCKET_DENSE_THRESHOLD` + `isBucketDense`, add:
+```ts
+/** Letters shown before a cluster needs a "show more" toggle (#827 redesign). */
+export const CLUSTER_PREVIEW = 5;
+```
+In `LetterBucket.svelte`: remove the `YearLetterStrip` import + the `dense`/strip branch. Add expand state and a visible-slice derived; render `CLUSTER_PREVIEW` compact cards, then a toggle when there are more:
+```svelte
+import { CLUSTER_PREVIEW, tagColorVar, type LetterBucket } from './timelineGrouping';
+import * as m from '$lib/paraglide/messages.js';
+// ...
+let expanded = $state(false);
+const visible = $derived(expanded ? bucket.letters : bucket.letters.slice(0, CLUSTER_PREVIEW));
+const hiddenCount = $derived(bucket.letters.length - CLUSTER_PREVIEW);
+```
+Body markup (replace the `{#if dense}…{:else}…` block):
+```svelte
+<ul class="space-y-1.5">
+	{#each visible as letter (entryKey(letter))}
+		<li><LetterCard entry={letter} variant={cardVariant} suppressTagChip={mode === 'thema'} compact={true} /></li>
+	{/each}
+</ul>
+{#if hiddenCount > 0}
+	<button
+		type="button"
+		data-testid="bucket-show-more"
+		aria-expanded={expanded}
+		onclick={() => (expanded = !expanded)}
+		style="display: inline-flex; align-items: center; min-height: 44px"
+		class="mt-1 px-1 font-sans text-xs font-semibold text-brand-navy hover:underline focus:outline-none focus-visible:ring-2 focus-visible:ring-brand-navy"
+	>
+		{expanded ? m.timeline_bucket_show_less() : m.timeline_bucket_show_more({ count: hiddenCount })}
+	</button>
+{/if}
+```
+
+- [ ] **Step 5: Run the tests — verify they pass.** Same command → PASS. Also run `src/lib/timeline/timelineGrouping.spec.ts --project=server` (still green; only constants changed).
+
+- [ ] **Step 6: Commit.**
+```bash
+npx prettier --write src/lib/timeline/LetterBucket.svelte src/lib/timeline/timelineGrouping.ts src/lib/timeline/LetterBucket.svelte.spec.ts messages/de.json messages/en.json messages/es.json
+cd .. && git add frontend/src/lib/timeline/LetterBucket.svelte frontend/src/lib/timeline/timelineGrouping.ts frontend/src/lib/timeline/LetterBucket.svelte.spec.ts frontend/messages/{de,en,es}.json
+git diff --cached --stat
+git commit -m "$(printf 'feat(timeline): cap grouped clusters at 5 letters with a show-more toggle\n\nReplaces the in-bucket month-density sparkline with a first-5 preview + show-more\n/ show-less toggle, the agreed grouped-view pattern. Datum mode keeps the >12\nYearLetterStrip.\n\nRefs #827')"
+```
+
+---
+
+## Task 2: Collapsed drawer for the leftover bin
+
+**Files:**
+- Modify: `frontend/src/lib/timeline/LetterBucket.svelte`
+- Test: `frontend/src/lib/timeline/LetterBucket.svelte.spec.ts`
+
+The fallback bucket (`kind === 'fallback'` — "Weitere Briefe"/"Ohne Thema") is a junk drawer: render it **collapsed** (count only, no letters) until the user reveals it; revealing shows the same first-5 + show-more body.
+
+- [ ] **Step 1: Write the failing tests.**
+```ts
+describe('LetterBucket — leftover drawer (#827 redesign)', () => {
+	const fb = (n: number, mode: 'event' | 'thema'): Bucket => ({
+		key: '__fallback__', kind: 'fallback', color: null,
+		letters: Array.from({ length: n }, (_, i) => makeEntry({ documentId: `f${i}`, eventDate: `1916-01-0${(i % 9) + 1}` }))
+	});
+	it('renders collapsed — count + reveal, no letter cards — until opened', () => {
+		render(LetterBucket, { bucket: fb(20, 'event'), mode: 'event', year: 1916 });
+		expect(document.querySelector('a.lcard')).toBeNull();
+		expect(document.body.textContent).toContain(m.timeline_bucket_other_letters());
+		expect(document.querySelector('[data-testid="bucket-reveal"]')).not.toBeNull();
+	});
+	it('reveals the first 5 letters when opened', async () => {
+		render(LetterBucket, { bucket: fb(20, 'event'), mode: 'event', year: 1916 });
+		(document.querySelector('[data-testid="bucket-reveal"]') as HTMLButtonElement).click();
+		await tick();
+		expect(document.querySelectorAll('a.lcard')).toHaveLength(5);
+		expect(document.querySelector('[data-testid="bucket-show-more"]')).not.toBeNull();
+	});
+});
+```
+
+- [ ] **Step 2: Run — verify fail.** `npx vitest run src/lib/timeline/LetterBucket.svelte.spec.ts --project=client` → FAIL.
+
+- [ ] **Step 3: Implement.** In `LetterBucket.svelte` add a `revealed` state defaulting to `bucket.kind !== 'fallback'` (non-drawers start open). Gate the body on it; when collapsed, render only the header + a reveal button:
+```svelte
+let revealed = $state(bucket.kind !== 'fallback');
+// header always renders; body only when revealed
+```
+Collapsed drawer markup (when `!revealed`): the fallback label + count already render in the header; add the reveal control:
+```svelte
+{#if !revealed}
+	<button type="button" data-testid="bucket-reveal" onclick={() => (revealed = true)}
+		style="display:inline-flex;align-items:center;min-height:44px"
+		class="px-1 font-sans text-xs font-semibold text-brand-navy hover:underline focus:outline-none focus-visible:ring-2 focus-visible:ring-brand-navy">
+		{m.timeline_bucket_show_more({ count: bucket.letters.length })}
+	</button>
+{:else}
+	<!-- the Task-1 body (ul + show-more) -->
+{/if}
+```
+Give the drawer a dashed neutral rail: add `class:border-dashed={bucket.kind === 'fallback'}` to the card.
+
+- [ ] **Step 4: Run — verify pass.** Same command → PASS. Re-run the Task-1 tests too (still green).
+
+- [ ] **Step 5: Commit.**
+```bash
+npx prettier --write src/lib/timeline/LetterBucket.svelte src/lib/timeline/LetterBucket.svelte.spec.ts
+cd .. && git add frontend/src/lib/timeline/LetterBucket.svelte frontend/src/lib/timeline/LetterBucket.svelte.spec.ts
+git diff --cached --stat
+git commit -m "$(printf 'feat(timeline): collapse the leftover Weitere-Briefe/Ohne-Thema bin to a drawer\n\nThe catch-all bucket renders count-only by default behind a reveal control, then\nexpands to the first-5 + show-more body. Keeps the junk drawer quiet instead of\nflooding the timeline.\n\nRefs #827')"
+```
+
+---
+
+## Task 3: Card chrome (the cluster is one contained card)
+
+**Files:**
+- Modify: `frontend/src/lib/timeline/LetterBucket.svelte`
+- Test: `frontend/src/lib/timeline/LetterBucket.svelte.spec.ts`
+
+Turn the `<section>` (rail-only, from PR #847) into a bordered card: `rounded` + `border border-line` + `bg-surface` + `shadow-sm`, keeping the coloured left rail (mint for event cluster, tag colour for tag, dashed neutral for the drawer). Header on a subtle `bg-canvas`/tint bar.
+
+- [ ] **Step 1: Write the failing test.**
+```ts
+it('renders the cluster as a contained card (bordered, rounded, surface)', () => {
+	const bucket: Bucket = { key: 'tag:t1', kind: 'tag', title: 'Krieg', color: 'sienna', letters: [makeEntry({ documentId: 'a' })] };
+	render(LetterBucket, { bucket, mode: 'thema', year: 1916 });
+	const card = document.querySelector('[data-testid="letter-bucket"]') as HTMLElement;
+	expect(card.className).toMatch(/\brounded\b|rounded-/);
+	expect(card.className).toContain('border');
+	expect(card.className).toContain('bg-surface');
+});
+```
+
+- [ ] **Step 2: Run — verify fail.** → FAIL (current section is `my-3 border-l-2 pl-3`, no `bg-surface`/`rounded`/full `border`).
+
+- [ ] **Step 3: Implement.** Update the `<section data-testid="letter-bucket">` classes to e.g.:
+```
+class="my-3 overflow-hidden rounded-md border border-line border-l-2 bg-surface shadow-sm"
+```
+keep `class:border-l-brand-mint={isEventCluster}`, `class:border-dashed={bucket.kind==='fallback'}`, and the inline `style={railStyle}` for the tag colour. Move the body padding inside (e.g. wrap header + body in a `px-3 py-2`), and give the header a tint bar (`bg-canvas` for events, plain for the drawer). Verify the existing "coloured left rail" test (`expect(section.style).toContain('var(--c-tag-sienna)')`) still holds — keep `railStyle` on the section.
+
+- [ ] **Step 4: Run — verify pass.** Run the whole `LetterBucket.svelte.spec.ts` → all PASS (including the PR #847 rail test).
+
+- [ ] **Step 5: Commit.**
+```bash
+npx prettier --write src/lib/timeline/LetterBucket.svelte src/lib/timeline/LetterBucket.svelte.spec.ts
+cd .. && git add frontend/src/lib/timeline/LetterBucket.svelte frontend/src/lib/timeline/LetterBucket.svelte.spec.ts
+git diff --cached --stat
+git commit -m "$(printf 'feat(timeline): make a grouped cluster one contained card\n\nWraps each cluster in a bordered, rounded surface card (keeping the colour rail)\nso the header and its letters read as a single unit.\n\nRefs #827')"
+```
+
+---
+
+## Task 4: Same-year curated event becomes the card header (kills the duplicate)
+
+**Files:**
+- Modify: `frontend/src/lib/timeline/LetterBucket.svelte` (add `event` + `canWrite` props + event-header rendering)
+- Modify: `frontend/src/lib/timeline/YearBand.svelte` (render the card in place of the pill for a same-year curated event)
+- Test: `frontend/src/lib/timeline/LetterBucket.svelte.spec.ts`, `frontend/src/lib/timeline/YearBand.svelte.spec.ts`
+
+When a curated event has letters in the same band, the event IS the card header — no separate pill. Reuse `getAccentConfig` (glyph/label) + `timelineDateLabel` + the `kuratiert/abgeleitet` provenance + the `✎` edit affordance (curated + eventId + canWrite), mirroring `EventPill.svelte`.
+
+- [ ] **Step 1: Write the failing tests.**
+
+`LetterBucket.svelte.spec.ts`:
+```ts
+import { getAccentConfig } from './eventCardConfig';
+it('renders the curated event as the card header when given an `event` (no separate pill)', () => {
+	const event = makeEntry({ kind: 'EVENT', type: 'PERSONAL', derived: false, eventId: 'e1',
+		title: 'Ein gewaltiger Stadtbrand', eventDate: '1916-07-06', senderName: '', receiverName: '', documentId: undefined });
+	const bucket: Bucket = { key: 'event:e1', kind: 'event', title: 'Ein gewaltiger Stadtbrand', color: null,
+		letters: [makeEntry({ documentId: 'a', linkedEventId: 'e1' })] };
+	render(LetterBucket, { bucket, mode: 'event', year: 1916, event, canWrite: true });
+	const header = document.querySelector('[data-testid="bucket-event-header"]') as HTMLElement;
+	expect(header.textContent).toContain('Ein gewaltiger Stadtbrand');
+	expect(header.textContent).toContain(m.timeline_provenance_curated());
+	expect(document.querySelector('[data-testid="event-edit"]')?.getAttribute('href')).toBe('/zeitstrahl/events/e1/edit');
+});
+it('shows no edit affordance in the header when canWrite is false', () => {
+	const event = makeEntry({ kind: 'EVENT', type: 'PERSONAL', derived: false, eventId: 'e1', title: 'X', senderName: '', receiverName: '', documentId: undefined });
+	const bucket: Bucket = { key: 'event:e1', kind: 'event', title: 'X', color: null, letters: [makeEntry({ documentId: 'a' })] };
+	render(LetterBucket, { bucket, mode: 'event', year: 1916, event, canWrite: false });
+	expect(document.querySelector('[data-testid="event-edit"]')).toBeNull();
+});
+```
+
+`YearBand.svelte.spec.ts` (replace/extend the PR #847 "nests an event cluster under its pill" test — the pill is now the card header):
+```ts
+it('renders a same-year curated event as one card header, with no separate pill and no duplicate title', () => {
+	const pill = makeEntry({ kind: 'EVENT', type: 'PERSONAL', derived: false, eventId: 'e1',
+		title: 'Ein gewaltiger Stadtbrand', eventDate: '1916-07-06', senderName: '', receiverName: '', documentId: undefined });
+	const letter = makeEntry({ documentId: 'a', linkedEventId: 'e1', eventDate: '1916-07-06' });
+	render(YearBand, { year: makeYear(1916, [pill, letter]), groupingMode: 'event', eventLookup: new Map([['e1', 'Ein gewaltiger Stadtbrand']]), canWrite: true });
+	const occurrences = (document.body.textContent ?? '').split('Ein gewaltiger Stadtbrand').length - 1;
+	expect(occurrences).toBe(1);                                  // once — in the card header
+	expect(document.querySelector('[data-testid="bucket-event-header"]')).not.toBeNull();
+	expect(document.querySelector('a.lcard.ev')).not.toBeNull();  // its letter, inside
+});
+```
+
+- [ ] **Step 2: Run — verify fail.** Both specs → FAIL.
+
+- [ ] **Step 3: Implement `LetterBucket` header.** Add props `event?: TimelineEntryDTO` and `canWrite = false`. Derive (mirroring `EventPill.svelte`):
+```svelte
+import { getAccentConfig } from './eventCardConfig';
+import { timelineDateLabel } from './dateLabel';
+// ...
+const accent = $derived(event ? getAccentConfig(event) : null);
+const eventDateLabel = $derived(event ? timelineDateLabel(event.eventDate, event.precision, event.eventDateEnd) : null);
+const provenance = $derived(event?.derived ? m.timeline_provenance_derived() : m.timeline_provenance_curated());
+const eventSubtitle = $derived(eventDateLabel ? `${eventDateLabel} · ${provenance}` : provenance);
+const canEdit = $derived(canWrite && !!event && !event.derived && event.eventId != null);
+```
+Header branch order: `if (event)` → event header (`data-testid="bucket-event-header"`: glyph from `accent.glyph` aria-hidden + sr-only `accent.label`, `event.title`, `eventSubtitle`, count, and the `✎` link `/zeitstrahl/events/{event.eventId}/edit` with `data-testid="event-edit"` when `canEdit`); else the existing `thema/tag` chip / `fallback` label branches.
+
+- [ ] **Step 4: Implement `YearBand` Ereignis branch.** When a curated event entry has a matching same-year bucket, render the card *instead of* the pill, passing `event={entry}` + `canWrite`; do **not** also push the `{ t: 'event' }` pill row for it. Letterless/derived/world events still push their pill/band row. Sketch:
+```svelte
+if (groupingMode === 'event') {
+	const buckets = bucketLetters(letters, 'event', eventLookup);
+	const sameYear = (id) => buckets.find((b) => b.kind === 'event' && b.key === `event:${id}`);
+	for (const entry of year.entries) {
+		if (entry.kind !== 'EVENT') continue;
+		const bucket = entry.eventId ? sameYear(entry.eventId) : undefined;
+		if (bucket) out.push({ t: 'eventcard', entry, bucket });   // card replaces pill
+		else out.push({ t: 'event', entry });                       // plain pill/band
+	}
+	for (const bucket of buckets) {
+		if (bucket.kind === 'fallback' || !year.entries.some((e) => e.kind === 'EVENT' && `event:${e.eventId}` === bucket.key))
+			out.push({ t: 'bucket', bucket, nested: false });         // cross-year cluster / drawer
+	}
+	return out;
+}
+```
+Add a `Row` variant `{ t: 'eventcard'; entry: TimelineEntryDTO; bucket: LetterBucketModel }` and template branch:
+```svelte
+{:else if row.t === 'eventcard'}
+	<LetterBucket bucket={row.bucket} mode="event" year={year.year} event={row.entry} canWrite={canWrite} />
+```
+Keep the existing `{ t: 'bucket' }` branch (cross-year clusters + drawer) rendering `<LetterBucket … nested={false} />` with no `event` prop → text header. Remember: **no `new Map`/`Set` in the component** — use `buckets.find` / `year.entries.some` as above.
+
+- [ ] **Step 5: Run — verify pass.** `npx vitest run src/lib/timeline/LetterBucket.svelte.spec.ts src/lib/timeline/YearBand.svelte.spec.ts src/lib/timeline/grouping-event-layer-identity.svelte.spec.ts --project=client` → PASS. The identity spec (REQ-001) still passes because derived/world fixtures are unchanged; if a now-stale assertion expects a pill for a *curated-with-letters* event, update it to expect the card header (REQ-001 amendment) and note it in the commit.
+
+- [ ] **Step 6: Commit.**
+```bash
+npx prettier --write src/lib/timeline/LetterBucket.svelte src/lib/timeline/YearBand.svelte src/lib/timeline/LetterBucket.svelte.spec.ts src/lib/timeline/YearBand.svelte.spec.ts
+cd .. && git add frontend/src/lib/timeline/LetterBucket.svelte frontend/src/lib/timeline/YearBand.svelte frontend/src/lib/timeline/LetterBucket.svelte.spec.ts frontend/src/lib/timeline/YearBand.svelte.spec.ts
+git diff --cached --stat
+git commit -m "$(printf 'feat(timeline): render a same-year curated event as its cluster card header\n\nA curated event with letters in its own band now becomes the contained card header\n(glyph, title, date, provenance, edit pencil) instead of a separate floating pill —\nthe title reads once. Derived life-events, world-bands, and letterless event pills\nare unchanged (REQ-001 amended for curated-with-letters).\n\nRefs #827')"
+```
+
+---
+
+## Task 5: Regression sweep + route view + docs
+
+**Files:**
+- Verify: route + cross-year + thema specs
+- Modify: `.specify/rtm.md`
+
+- [ ] **Step 1: Run the affected specs (client).**
+```
+npx vitest run \
+  src/lib/timeline/BucketHeaderChip.svelte.spec.ts src/lib/timeline/LetterCard.svelte.spec.ts \
+  src/lib/timeline/LetterBucket.svelte.spec.ts src/lib/timeline/YearBand.svelte.spec.ts \
+  src/lib/timeline/GroupingControl.svelte.spec.ts src/lib/timeline/grouping-event-layer-identity.svelte.spec.ts \
+  src/lib/timeline/TimelineView.svelte.spec.ts src/routes/zeitstrahl/page.svelte.spec.ts --project=client
+```
+Expected: all PASS. Fix any cross-year/thema spec that assumed the old header (it should now find the card; thema card header is still the `BucketHeaderChip`).
+
+- [ ] **Step 2: Run the server specs.** `npx vitest run src/lib/timeline/timelineGrouping.spec.ts src/lib/timeline/timeline-no-raw-html.spec.ts src/lib/messages.spec.ts --project=server` → PASS. If `messages.spec.ts` parity fails, it's the two new keys — they must be in de/en/es.
+
+- [ ] **Step 3: Type-check the changed files.** `npm run check 2>&1 | grep -E "LetterBucket|YearBand|timelineGrouping"` → no ERROR lines (baseline noise elsewhere is fine).
+
+- [ ] **Step 4: Update the RTM.** In `.specify/rtm.md`, edit REQ-014 (event-clustered letters live inside a contained card whose header is the same-year event; first-5 + show-more) and REQ-020 (clusters are contained cards with a 5-letter preview + show-more; the leftover bin is a collapsed drawer; the sparkline is no longer used in grouped mode), citing the new tests.
+
+- [ ] **Step 5: Commit.**
+```bash
+cd .. && git add .specify/rtm.md
+git diff --cached --stat
+git commit -m "$(printf 'docs(rtm): trace the grouped-view contained-card layout (#827)\n\nRefs #827')"
+```
+
+- [ ] **Step 6: Push.** `git push origin feat/issue-827-zeitstrahl-grouping`
+
+---
+
+## Self-Review notes (author)
+
+- **Spec coverage:** contained card (Task 3) ✓; first-5 + show-more (Task 1) ✓; collapsed drawer (Task 2) ✓; same-year event → card header / no duplicate (Task 4) ✓; derived/world unchanged (Task 4 keeps plain rows) ✓; thema chip header reused (existing, verified Task 5) ✓; cross-year text header (existing `{t:'bucket'}` path, verified Task 5) ✓; sparkline dropped from grouped mode (Task 1) ✓.
+- **Naming consistency:** `CLUSTER_PREVIEW` (Task 1) used in Tasks 1–2; testids `bucket-show-more` / `bucket-reveal` / `bucket-event-header` / `event-edit` consistent across tasks; `Row` variant `eventcard` defined and consumed in Task 4.
+- **REQ-001 amendment** is intentional and documented in the spec; Task 4 Step 5 flags fixing any stale identity assertion.

docs/superpowers/specs/2026-06-15-zeitstrahl-grouped-view-layout-design.md

@@ -0,0 +1,102 @@
+# Zeitstrahl grouped-view layout redesign
+
+**Date:** 2026-06-15
+**Feature:** #827 (regroup `/zeitstrahl` by Ereignis/Thema) — layout follow-up on PR #847
+**Status:** Approved (brainstorm), pending implementation plan
+
+> The REQ contract for #827 lives in the Gitea issue body (and the amendment comment of
+> 2026-06-15). This document records the **layout/visual design** agreed in the visual
+> brainstorm and the REQ deltas it implies. Mockups: `.superpowers/brainstorm/*/content/`.
+
+## Problem
+
+The first grouped-view implementation (PR #847) fixed the flood and the duplicate event title,
+but two issues remained on review of the live view:
+
+1. **Weak belonging.** A clustered event's letters dropped below its centered pill as a
+   full-width block with only a thin left rail. The connection between an event and its letters
+   read weakly — the eye couldn't tell the letters belonged to the pill above.
+2. **Layout inconsistency.** In Datum mode letters alternate left/right of the centered spine
+   (events/density centered). In grouped mode the letters became full-width, breaking that
+   rhythm with no clear reason.
+
+## Decision: a cluster is one contained card
+
+A clustered event (Ereignis) or root tag (Thema) renders as **one bordered card** whose header
+is the event/tag itself and whose body holds that cluster's letters. Belonging becomes
+structural (a single container), not positional guesswork. This replaces the full-width block.
+
+### Ereignis mode, per year band
+
+1. **Derived life-events** (Geburt/Tod/Heirat, `abgeleitet`) never cluster — they carry no
+   document links, so they are always **plain axis fixtures, unchanged from Datum mode**. A
+   **world-band** (`historisch`) is normally letterless and stays a plain band; on the rare
+   occasion a historical event has linked letters it follows rule 2 (becomes a card).
+2. **A curated event (PERSONAL or HISTORICAL) with letters in this band** → one mint-bordered card:
+   - **Header** = the event's glyph + title + date + `kuratiert` + edit-✎ + count (the pill's
+     content, laid out as a header bar). This *replaces* the separate floating pill for that
+     event in this band — killing the duplicate title.
+   - **Body** = the cluster's letters, **first 5 shown, then a "+ N weitere Briefe anzeigen"
+     toggle** that expands/collapses the rest. Letters use the compact `LetterCard` variant.
+3. **A curated event with no letters in this band** → stays a plain centered pill (no empty card).
+4. **A curated event whose letters fall in a different year than its pill** → those letters form a
+   labeled card in *their* year (header = event name as text, no ✎/pill since the pill lives
+   elsewhere); the pill stays in its own band. No adjacent duplication.
+5. **Leftover letters** (linked to no surviving curated event) → a collapsed neutral, dashed
+   **"✉ N Briefe ohne Ereignis · anzeigen ›"** drawer. Clicking expands to the same first-5 +
+   show-more list. No preview letters until opened.
+
+### Thema mode
+
+Identical shape. Each card's header is the **tinted root-tag chip** (`● Krieg · 24`,
+`BucketHeaderChip`, fixed-ink label per the contrast fix) instead of an event pill; there is no
+axis pill for a tag, so every tag cluster is a standalone card. The per-letter `TagChip` stays
+suppressed inside its own card (REQ-017). The leftover drawer reads **"Ohne Thema"**.
+
+### Layout / spine
+
+- Cluster cards are **centered on the spine** (like events already are), not full-width-flush —
+  consistent with how grouped units (events) relate to the axis. Individual chronological
+  letters keep alternating left/right only in **Datum** mode.
+- Each card carries a colour left rail: **mint** for an Ereignis cluster, the **tag colour** for
+  a Thema cluster, **neutral dashed** for the leftover drawer.
+
+## Components affected
+
+- `LetterBucket.svelte` — becomes the contained card: header slot (pill-content / tag chip /
+  drawer label / cross-year text label) + body with the first-5 cap and the show-more toggle.
+  Drop the `YearLetterStrip` (sparkline) branch from grouped mode.
+- `YearBand.svelte` — in Ereignis mode, a same-year curated event renders *as* the card header
+  (merge pill into the card) instead of pill-then-nested-bucket; derived/world/letterless events
+  stay plain; cross-year clusters and the leftover drawer render after the axis entries.
+- `LetterCard.svelte` — compact variant already exists (PR #847); reused inside cards.
+- `BucketHeaderChip.svelte` — reused as the Thema card header (contrast fix already shipped).
+- `timelineGrouping.ts` — the first-visible cap (`CLUSTER_PREVIEW = 5`) replaces
+  `BUCKET_DENSE_THRESHOLD`; helpers unchanged otherwise.
+- Possibly a small `ClusterCard`/header sub-component if `LetterBucket` grows too large.
+
+## REQ deltas (to fold into issue #827)
+
+- **REQ-001 (amended):** derived life-events, world-bands, and *letterless* curated event pills
+  render identically across modes; a curated event **that has letters** renders as its cluster
+  card's header in grouped mode (no longer byte-identical to its Datum pill). Every event keeps
+  its spine position (year).
+- **REQ-003 / REQ-014 (amended):** event-clustered letters live inside a contained card; the
+  header is the event (same-year) or a text label (cross-year). First 5 shown + show-more.
+- **REQ-020 (amended):** grouped clusters are contained colour-railed cards with a first-5
+  preview + show-more toggle; the leftover bin is a collapsed count-only drawer. The
+  month-density `YearLetterStrip` is **no longer used in grouped mode** (still used in Datum
+  dense years).
+
+## Out of scope
+
+- Datum mode (untouched — keeps the alternating-axis zigzag and the >12 sparkline strip).
+- Backend / DTO (`linkedEventId` and root-tag fields already shipped; no change).
+- New i18n beyond a show-more / drawer label string set.
+
+## Testing approach
+
+TDD per component, mirroring PR #847: `LetterBucket` (card header variants, first-5 cap,
+show-more expand/collapse, drawer collapsed-by-default, colour rail), `YearBand` (same-year merge
+= no duplicate title; cross-year keeps a label; derived/world pills unchanged), and the route
+spec for the assembled view. Run targeted `--project=client` / `--project=server` specs only.

frontend/CLAUDE.md

@@ -50,7 +50,7 @@ src/
 │   │   ├── relationship/ # Relationship form + chip components
 │   │   └── genealogy/   # Stammbaum (family tree) components
 │   ├── tag/             # Tag domain: TagInput, TagChipList, TagParentPicker
-│   ├── timeline/        # Timeline (Zeitstrahl) domain: TimelineView, YearBand, EventPill, WorldBand, LetterCard, YearLetterStrip, GapSpan; dateLabel + timelineDensity + eventCardConfig (imports $lib/shared only, never document/)
+│   ├── timeline/        # Timeline (Zeitstrahl) domain: TimelineView, YearBand, EventPill, WorldBand, LetterCard, LetterBucket, BucketHeaderChip, GroupingControl, TagChip, YearLetterStrip, GapSpan; dateLabel + timelineDensity + timelineFilter + timelineGrouping + eventCardConfig (imports $lib/shared only, never document/)
 │   ├── geschichte/      # Geschichte (story) domain: editor + card
 │   ├── notification/    # Notification bell + dropdown + store
 │   ├── activity/        # Activity feed (Chronik) components

frontend/e2e/zeitstrahl-filter.spec.ts

@@ -0,0 +1,93 @@
+import AxeBuilder from '@axe-core/playwright';
+import { test, expect, type APIRequestContext } from '@playwright/test';
+
+/**
+ * Global /zeitstrahl layer filter (#780). Runs against the real stack with the
+ * seeded admin session (auth.setup). Covers the primary journey (hide the
+ * Letters layer → letter cards vanish + the trigger reports one active filter →
+ * reset restores everything) and a 375px axe pass with the collapsible open in
+ * both light and dark mode.
+ *
+ * #779 (the /zeitstrahl route) is merged, so this spec is NOT skipped. Per
+ * e2e/CLAUDE.md, E2E is not yet wired into CI — this axe gate runs locally only
+ * for now.
+ */
+
+const stamp = () => new Date().toISOString().replace(/[^0-9]/g, '');
+
+async function createPerson(request: APIRequestContext, firstName: string, lastName: string) {
+	const res = await request.post('/api/persons', {
+		data: { personType: 'PERSON', firstName, lastName }
+	});
+	if (!res.ok()) throw new Error(`create person failed: ${res.status()}`);
+	return (await res.json()).id as string;
+}
+
+/** Seeds one dated letter so the timeline has content (and a LetterCard to hide). */
+async function seedDatedLetter(request: APIRequestContext, isoDate: string, title: string) {
+	const senderId = await createPerson(request, 'Filter-Test', `Absender ${stamp()}`);
+	const receiverId = await createPerson(request, 'Filter-Test', `Empfaenger ${stamp()}`);
+
+	const createRes = await request.post('/api/documents', { multipart: { title } });
+	if (!createRes.ok()) throw new Error(`create document failed: ${createRes.status()}`);
+	const docId = (await createRes.json()).id as string;
+
+	const put = await request.put(`/api/documents/${docId}`, {
+		multipart: {
+			title,
+			documentDate: isoDate,
+			metaDatePrecision: 'DAY',
+			senderId,
+			receiverIds: receiverId
+		}
+	});
+	if (!put.ok()) throw new Error(`update document failed: ${put.status()}`);
+}
+
+test.describe('Zeitstrahl — layer filter (#780)', () => {
+	test('hiding the Letters layer removes letter cards and reports the active count; reset restores', async ({
+		page,
+		request
+	}) => {
+		// A sparse year keeps the seeded letter an individual card (not a dense strip).
+		const title = `E2E Filter Brief ${stamp()}`;
+		await seedDatedLetter(request, '1903-03-03', title);
+
+		await page.goto('/zeitstrahl');
+		await page.waitForSelector('[data-hydrated]');
+		await expect(page.getByText(title)).toBeVisible();
+
+		await page.getByTestId('timeline-filter-trigger').click();
+		await page.getByTestId('timeline-filter-letters').click();
+
+		await expect(page.getByText(title)).toHaveCount(0);
+		await expect(page.getByTestId('timeline-filter-trigger')).toContainText('1 aktiv');
+
+		await page.getByTestId('timeline-filter-reset').click();
+		await expect(page.getByText(title)).toBeVisible();
+	});
+
+	test('no wcag2a/wcag2aa violations at 375px with the filter bar open (light + dark)', async ({
+		page,
+		request
+	}) => {
+		await seedDatedLetter(request, '1915-06-15', `E2E Filter A11y ${stamp()}`);
+
+		await page.setViewportSize({ width: 375, height: 800 });
+		await page.goto('/zeitstrahl');
+		await page.waitForSelector('[data-hydrated]');
+
+		// Open the collapsible so axe scans the toggles, not just the trigger.
+		await page.getByTestId('timeline-filter-trigger').click();
+		await expect(page.getByTestId('timeline-filter-personal')).toBeVisible();
+
+		const scan = () => new AxeBuilder({ page }).withTags(['wcag2a', 'wcag2aa']).analyze();
+
+		const light = await scan();
+		expect(light.violations, JSON.stringify(light.violations, null, 2)).toEqual([]);
+
+		await page.evaluate(() => document.documentElement.setAttribute('data-theme', 'dark'));
+		const dark = await scan();
+		expect(dark.violations, JSON.stringify(dark.violations, null, 2)).toEqual([]);
+	});
+});

frontend/e2e/zeitstrahl-grouping.spec.ts

@@ -0,0 +1,123 @@
+import AxeBuilder from '@axe-core/playwright';
+import { test, expect, type APIRequestContext } from '@playwright/test';
+
+/**
+ * Global /zeitstrahl grouping toggle (#827). Runs against the real stack with the seeded admin
+ * session (auth.setup). Covers REQ-002 (switching modes issues zero extra GET /api/timeline
+ * requests — the regroup is client-side), REQ-011 (the control stays usable and overflow-free at
+ * 320px with full-word aria-labels and ≥44px tap targets), and REQ-010g (a 320px axe pass over
+ * the control in both light and dark mode).
+ *
+ * Per e2e/CLAUDE.md, E2E is not yet wired into CI — this gate runs locally for now, like the
+ * #780 layer-filter spec it mirrors.
+ */
+
+const stamp = () => new Date().toISOString().replace(/[^0-9]/g, '');
+
+async function createPerson(request: APIRequestContext, firstName: string, lastName: string) {
+	const res = await request.post('/api/persons', {
+		data: { personType: 'PERSON', firstName, lastName }
+	});
+	if (!res.ok()) throw new Error(`create person failed: ${res.status()}`);
+	return (await res.json()).id as string;
+}
+
+/** Seeds one dated letter so the timeline has a loose letter and the grouping control is enabled. */
+async function seedDatedLetter(request: APIRequestContext, isoDate: string, title: string) {
+	const senderId = await createPerson(request, 'Group-Test', `Absender ${stamp()}`);
+	const receiverId = await createPerson(request, 'Group-Test', `Empfaenger ${stamp()}`);
+
+	const createRes = await request.post('/api/documents', { multipart: { title } });
+	if (!createRes.ok()) throw new Error(`create document failed: ${createRes.status()}`);
+	const docId = (await createRes.json()).id as string;
+
+	const put = await request.put(`/api/documents/${docId}`, {
+		multipart: {
+			title,
+			documentDate: isoDate,
+			metaDatePrecision: 'DAY',
+			senderId,
+			receiverIds: receiverId
+		}
+	});
+	if (!put.ok()) throw new Error(`update document failed: ${put.status()}`);
+}
+
+test.describe('Zeitstrahl — grouping toggle (#827)', () => {
+	test('switching grouping modes issues no extra timeline fetch (REQ-002)', async ({
+		page,
+		request
+	}) => {
+		await seedDatedLetter(request, '1909-05-05', `E2E Group Brief ${stamp()}`);
+
+		let timelineRequests = 0;
+		page.on('request', (req) => {
+			if (req.url().includes('/api/timeline')) timelineRequests++;
+		});
+
+		await page.goto('/zeitstrahl');
+		await page.waitForSelector('[data-hydrated]');
+		await expect(page.getByTestId('grouping-control')).toBeVisible();
+
+		const afterLoad = timelineRequests;
+		await page.locator('[data-value="event"]').click();
+		await page.locator('[data-value="thema"]').click();
+		await page.locator('[data-value="date"]').click();
+
+		// the regroup is a pure client-side transform — not one more GET /api/timeline
+		expect(timelineRequests).toBe(afterLoad);
+	});
+
+	test('the control stays overflow-free and operable at 320px (REQ-011)', async ({
+		page,
+		request
+	}) => {
+		await seedDatedLetter(request, '1911-02-02', `E2E Group 320 ${stamp()}`);
+
+		await page.setViewportSize({ width: 320, height: 800 });
+		await page.goto('/zeitstrahl');
+		await page.waitForSelector('[data-hydrated]');
+
+		const control = page.getByTestId('grouping-control');
+		await expect(control).toBeVisible();
+
+		// the control fits inside the 320px viewport — no horizontal overflow
+		const box = await control.boundingBox();
+		expect(box).not.toBeNull();
+		expect(box!.x + box!.width).toBeLessThanOrEqual(321);
+
+		for (const [value, fullWord] of [
+			['date', 'Datum'],
+			['event', 'Ereignis'],
+			['thema', 'Thema']
+		]) {
+			const radio = page.locator(`[data-value="${value}"]`);
+			const radioBox = await radio.boundingBox();
+			expect(radioBox!.height).toBeGreaterThanOrEqual(44);
+			expect(radioBox!.width).toBeGreaterThanOrEqual(44);
+			// the abbreviated segment still announces its full word
+			expect(await radio.getAttribute('aria-label')).toBe(fullWord);
+		}
+	});
+
+	test('no wcag2a/wcag2aa violations on the grouping control at 320px (light + dark) (REQ-010g)', async ({
+		page,
+		request
+	}) => {
+		await seedDatedLetter(request, '1915-06-15', `E2E Group A11y ${stamp()}`);
+
+		await page.setViewportSize({ width: 320, height: 800 });
+		await page.goto('/zeitstrahl');
+		await page.waitForSelector('[data-hydrated]');
+		await expect(page.getByTestId('grouping-control')).toBeVisible();
+
+		const scan = () => new AxeBuilder({ page }).withTags(['wcag2a', 'wcag2aa']).analyze();
+
+		const light = await scan();
+		expect(light.violations, JSON.stringify(light.violations, null, 2)).toEqual([]);
+
+		await page.evaluate(() => document.documentElement.setAttribute('data-theme', 'dark'));
+		const dark = await scan();
+		expect(dark.violations, JSON.stringify(dark.violations, null, 2)).toEqual([]);
+	});
+});

frontend/messages/de.json

@@ -188,6 +188,7 @@
 	"person_hint_generation": "Generation in der Familie (G 0 = älteste Generation)",
 	"person_year_error": "Bitte eine vierstellige Jahreszahl eingeben",
 	"person_years_error_order": "Geburtsjahr muss vor dem Todesjahr liegen",
+	"person_add_event": "Ereignis für diese Person",
 	"person_docs_heading": "Gesendete Dokumente",
 	"person_no_docs": "Diese Person ist noch nicht als Absender verknüpft.",
 	"person_received_docs_heading": "Empfangene Dokumente",
@@ -651,6 +652,7 @@
 	"error_invalid_date_range": "Das Enddatum darf nicht vor dem Startdatum liegen.",
 	"error_birth_after_death": "Geburtsdatum muss vor dem Sterbedatum liegen. Tipp: Falls nur das Todesjahr bekannt ist und der Geburtstag spät im selben Jahr lag, bitte das Folgejahr eintragen.",
 	"error_invalid_date_precision": "Datum und Genauigkeit stimmen nicht überein.",
+	"error_invalid_relationship_dates": "Das Ende-Datum darf nicht vor dem Beginn-Datum liegen.",
 	"validation_last_name_required": "Nachname ist Pflichtfeld.",
 	"validation_first_name_required": "Vorname ist Pflichtfeld.",
 	"error_ocr_service_unavailable": "Der OCR-Dienst ist nicht verfügbar.",
@@ -1034,6 +1036,7 @@
 	"nav_geschichten": "Geschichten",
 	"nav_zeitstrahl": "Zeitstrahl",
 	"timeline_heading": "Zeitstrahl",
+	"timeline_add_event": "Ereignis hinzufügen",
 	"timeline_empty_state": "Noch keine Ereignisse.",
 	"timeline_undated_section": "Ohne Datum",
 	"timeline_unknown_person": "Unbekannt",
@@ -1047,6 +1050,21 @@
 	"timeline_derived_death": "Tod",
 	"timeline_derived_marriage": "Heirat",
 	"timeline_grouping_date": "Gruppierung: Datum",
+	"timeline_grouping_event": "Gruppierung: Ereignis",
+	"timeline_grouping_thema": "Gruppierung: Thema",
+	"timeline_grouping_aria_label": "Gruppierung",
+	"timeline_grouping_segment_date": "Datum",
+	"timeline_grouping_segment_event": "Ereignis",
+	"timeline_grouping_segment_thema": "Thema",
+	"timeline_grouping_segment_date_short": "Dat.",
+	"timeline_grouping_segment_event_short": "Ereig.",
+	"timeline_grouping_segment_thema_short": "Thema",
+	"timeline_grouping_disabled_reason": "Briefe sind ausgeblendet – es gibt nichts zu gruppieren.",
+	"timeline_grouping_multitag_hint": "Brief mit mehreren Tags erscheint unter seinem primären Tag.",
+	"timeline_bucket_other_letters": "Weitere Briefe",
+	"timeline_bucket_no_topic": "Ohne Thema",
+	"timeline_bucket_show_more": "+ {count} weitere Briefe anzeigen",
+	"timeline_bucket_show_less": "Weniger anzeigen",
 	"timeline_provenance_derived": "abgeleitet",
 	"timeline_provenance_curated": "kuratiert",
 	"timeline_letter_glyph_label": "Brief",
@@ -1056,6 +1074,14 @@
 	"timeline_events_count": "{count} Ereignisse",
 	"timeline_letters_count_singular": "1 Brief",
 	"timeline_events_count_singular": "1 Ereignis",
+	"timeline_filter_label_layers": "Ebenen anzeigen",
+	"timeline_filter_layer_personal": "Persönliche Ereignisse",
+	"timeline_filter_layer_historical": "Historische Ereignisse",
+	"timeline_filter_layer_letters": "Briefe",
+	"timeline_filter_trigger": "Filter",
+	"timeline_filter_trigger_active": "Filter ({count} aktiv)",
+	"timeline_filter_reset": "Filter zurücksetzen",
+	"timeline_filter_empty_state": "Keine Einträge entsprechen diesen Filtern.",
 	"event_editor_new_title": "Neues Ereignis",
 	"event_editor_edit_title": "Ereignis bearbeiten",
 	"event_editor_section_when": "Wann",
@@ -1221,6 +1247,16 @@
 	"relation_form_field_from_year": "Von Jahr",
 	"relation_form_field_to_year": "Bis Jahr",
 	"relation_form_year_placeholder": "z.B. 1920",
+	"relation_label_from_date": "Beginn (Datum)",
+	"relation_label_to_date": "Ende (Datum)",
+	"relation_label_date_precision": "Genauigkeit",
+	"relation_precision_day": "Genaues Datum (Tag)",
+	"relation_precision_month": "Monat bekannt",
+	"relation_precision_year": "Nur Jahreszahl",
+	"relation_label_notes": "Notizen",
+	"relation_notes_placeholder": "Optionaler Hinweis zu dieser Beziehung",
+	"relation_date_placeholder_hint": "Leer lassen, wenn unbekannt",
+	"relation_edit": "Beziehung bearbeiten",
 	"person_relationships_heading": "Beziehungen",
 	"person_relationships_empty": "Noch keine Beziehungen bekannt.",
 	"timeline_aria_label": "Zeitachse Dokumentdichte",

frontend/messages/en.json

@@ -188,6 +188,7 @@
 	"person_hint_generation": "Generation within the family (G 0 = oldest generation)",
 	"person_year_error": "Please enter a four-digit year",
 	"person_years_error_order": "Birth year must be before death year",
+	"person_add_event": "Add event for this person",
 	"person_docs_heading": "Sent documents",
 	"person_no_docs": "This person has not yet been linked as a sender.",
 	"person_received_docs_heading": "Received documents",
@@ -651,6 +652,7 @@
 	"error_invalid_date_range": "The end date must not be before the start date.",
 	"error_birth_after_death": "Birth date must be before death date. Tip: if only the death year is known and the birthday is late in the same year, enter the following year.",
 	"error_invalid_date_precision": "Date and precision do not match.",
+	"error_invalid_relationship_dates": "The end date must not be before the start date.",
 	"validation_last_name_required": "Last name is required.",
 	"validation_first_name_required": "First name is required.",
 	"error_ocr_service_unavailable": "The OCR service is not available.",
@@ -1034,6 +1036,7 @@
 	"nav_geschichten": "Stories",
 	"nav_zeitstrahl": "Timeline",
 	"timeline_heading": "Timeline",
+	"timeline_add_event": "Add event",
 	"timeline_empty_state": "No events yet.",
 	"timeline_undated_section": "Without Date",
 	"timeline_unknown_person": "Unknown",
@@ -1047,6 +1050,21 @@
 	"timeline_derived_death": "Death",
 	"timeline_derived_marriage": "Marriage",
 	"timeline_grouping_date": "Grouping: Date",
+	"timeline_grouping_event": "Grouping: Event",
+	"timeline_grouping_thema": "Grouping: Topic",
+	"timeline_grouping_aria_label": "Grouping",
+	"timeline_grouping_segment_date": "Date",
+	"timeline_grouping_segment_event": "Event",
+	"timeline_grouping_segment_thema": "Topic",
+	"timeline_grouping_segment_date_short": "Date",
+	"timeline_grouping_segment_event_short": "Event",
+	"timeline_grouping_segment_thema_short": "Topic",
+	"timeline_grouping_disabled_reason": "Letters are hidden — there is nothing to group.",
+	"timeline_grouping_multitag_hint": "A letter with several tags appears under its primary tag.",
+	"timeline_bucket_other_letters": "More letters",
+	"timeline_bucket_no_topic": "No topic",
+	"timeline_bucket_show_more": "+ {count} more letters",
+	"timeline_bucket_show_less": "Show fewer",
 	"timeline_provenance_derived": "derived",
 	"timeline_provenance_curated": "curated",
 	"timeline_letter_glyph_label": "Letter",
@@ -1056,6 +1074,14 @@
 	"timeline_events_count": "{count} events",
 	"timeline_letters_count_singular": "1 letter",
 	"timeline_events_count_singular": "1 event",
+	"timeline_filter_label_layers": "Show layers",
+	"timeline_filter_layer_personal": "Personal events",
+	"timeline_filter_layer_historical": "Historical events",
+	"timeline_filter_layer_letters": "Letters",
+	"timeline_filter_trigger": "Filter",
+	"timeline_filter_trigger_active": "Filter ({count} active)",
+	"timeline_filter_reset": "Reset filters",
+	"timeline_filter_empty_state": "No entries match these filters.",
 	"event_editor_new_title": "New event",
 	"event_editor_edit_title": "Edit event",
 	"event_editor_section_when": "When",
@@ -1221,6 +1247,16 @@
 	"relation_form_field_from_year": "From year",
 	"relation_form_field_to_year": "To year",
 	"relation_form_year_placeholder": "e.g. 1920",
+	"relation_label_from_date": "Start date",
+	"relation_label_to_date": "End date",
+	"relation_label_date_precision": "Precision",
+	"relation_precision_day": "Exact date (day)",
+	"relation_precision_month": "Month known",
+	"relation_precision_year": "Year only",
+	"relation_label_notes": "Notes",
+	"relation_notes_placeholder": "Optional note about this relationship",
+	"relation_date_placeholder_hint": "Leave empty if unknown",
+	"relation_edit": "Edit relationship",
 	"person_relationships_heading": "Relationships",
 	"person_relationships_empty": "No relationships known yet.",
 	"timeline_aria_label": "Document density timeline",

frontend/messages/es.json

@@ -188,6 +188,7 @@
 	"person_hint_generation": "Generación dentro de la familia (G 0 = generación más antigua)",
 	"person_year_error": "Introduzca un año de cuatro dígitos",
 	"person_years_error_order": "El año de nacimiento debe ser anterior al año de fallecimiento",
+	"person_add_event": "Añadir evento para esta persona",
 	"person_docs_heading": "Documentos enviados",
 	"person_no_docs": "Esta persona aún no está vinculada como remitente.",
 	"person_received_docs_heading": "Documentos recibidos",
@@ -651,6 +652,7 @@
 	"error_invalid_date_range": "La fecha final no puede ser anterior a la inicial.",
 	"error_birth_after_death": "La fecha de nacimiento debe ser anterior a la de defunción.",
 	"error_invalid_date_precision": "La fecha y la precisión no coinciden.",
+	"error_invalid_relationship_dates": "La fecha de fin no puede ser anterior a la de inicio.",
 	"validation_last_name_required": "El apellido es obligatorio.",
 	"validation_first_name_required": "El nombre es obligatorio.",
 	"error_ocr_service_unavailable": "El servicio OCR no está disponible.",
@@ -1034,6 +1036,7 @@
 	"nav_geschichten": "Historias",
 	"nav_zeitstrahl": "Línea de tiempo",
 	"timeline_heading": "Línea de tiempo",
+	"timeline_add_event": "Añadir evento",
 	"timeline_empty_state": "Aún no hay eventos.",
 	"timeline_undated_section": "Sin Fecha",
 	"timeline_unknown_person": "Desconocido",
@@ -1047,6 +1050,21 @@
 	"timeline_derived_death": "Fallecimiento",
 	"timeline_derived_marriage": "Matrimonio",
 	"timeline_grouping_date": "Agrupación: Fecha",
+	"timeline_grouping_event": "Agrupación: Evento",
+	"timeline_grouping_thema": "Agrupación: Tema",
+	"timeline_grouping_aria_label": "Agrupación",
+	"timeline_grouping_segment_date": "Fecha",
+	"timeline_grouping_segment_event": "Evento",
+	"timeline_grouping_segment_thema": "Tema",
+	"timeline_grouping_segment_date_short": "Fecha",
+	"timeline_grouping_segment_event_short": "Evento",
+	"timeline_grouping_segment_thema_short": "Tema",
+	"timeline_grouping_disabled_reason": "Las cartas están ocultas: no hay nada que agrupar.",
+	"timeline_grouping_multitag_hint": "Una carta con varias etiquetas aparece bajo su etiqueta principal.",
+	"timeline_bucket_other_letters": "Más cartas",
+	"timeline_bucket_no_topic": "Sin tema",
+	"timeline_bucket_show_more": "+ {count} cartas más",
+	"timeline_bucket_show_less": "Mostrar menos",
 	"timeline_provenance_derived": "derivado",
 	"timeline_provenance_curated": "curado",
 	"timeline_letter_glyph_label": "Carta",
@@ -1056,6 +1074,14 @@
 	"timeline_events_count": "{count} eventos",
 	"timeline_letters_count_singular": "1 carta",
 	"timeline_events_count_singular": "1 evento",
+	"timeline_filter_label_layers": "Mostrar capas",
+	"timeline_filter_layer_personal": "Eventos personales",
+	"timeline_filter_layer_historical": "Eventos históricos",
+	"timeline_filter_layer_letters": "Cartas",
+	"timeline_filter_trigger": "Filtro",
+	"timeline_filter_trigger_active": "Filtro ({count} activos)",
+	"timeline_filter_reset": "Restablecer filtros",
+	"timeline_filter_empty_state": "Ninguna entrada coincide con estos filtros.",
 	"event_editor_new_title": "Nuevo evento",
 	"event_editor_edit_title": "Editar evento",
 	"event_editor_section_when": "Cuándo",
@@ -1221,6 +1247,16 @@
 	"relation_form_field_from_year": "Desde año",
 	"relation_form_field_to_year": "Hasta año",
 	"relation_form_year_placeholder": "ej. 1920",
+	"relation_label_from_date": "Fecha de inicio",
+	"relation_label_to_date": "Fecha de fin",
+	"relation_label_date_precision": "Precisión",
+	"relation_precision_day": "Fecha exacta (día)",
+	"relation_precision_month": "Mes conocido",
+	"relation_precision_year": "Solo año",
+	"relation_label_notes": "Notas",
+	"relation_notes_placeholder": "Nota opcional sobre esta relación",
+	"relation_date_placeholder_hint": "Dejar vacío si es desconocido",
+	"relation_edit": "Editar relación",
 	"person_relationships_heading": "Relaciones",
 	"person_relationships_empty": "Aún no se conocen relaciones.",
 	"timeline_aria_label": "Cronología de densidad de documentos",

frontend/src/lib/generated/api.ts

@@ -100,6 +100,22 @@ export interface paths {
         patch?: never;
         trace?: never;
     };
+    "/api/persons/{id}/relationships/{relId}": {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        get?: never;
+        put: operations["updateRelationship"];
+        post?: never;
+        delete: operations["deleteRelationship"];
+        options?: never;
+        head?: never;
+        patch?: never;
+        trace?: never;
+    };
     "/api/geschichten/{id}/items/reorder": {
         parameters: {
             query?: never;
@@ -1640,22 +1656,6 @@ export interface paths {
         patch?: never;
         trace?: never;
     };
-    "/api/persons/{id}/relationships/{relId}": {
-        parameters: {
-            query?: never;
-            header?: never;
-            path?: never;
-            cookie?: never;
-        };
-        get?: never;
-        put?: never;
-        post?: never;
-        delete: operations["deleteRelationship"];
-        options?: never;
-        head?: never;
-        patch?: never;
-        trace?: never;
-    };
     "/api/persons/{id}/aliases/{aliasId}": {
         parameters: {
             query?: never;
@@ -1853,6 +1853,50 @@ export interface components {
             provisional: boolean;
             readonly displayName: string;
         };
+        RelationshipUpsertRequest: {
+            /** Format: uuid */
+            relatedPersonId: string;
+            /** @enum {string} */
+            relationType: "PARENT_OF" | "SPOUSE_OF" | "SIBLING_OF" | "FRIEND" | "COLLEAGUE" | "EMPLOYER" | "DOCTOR" | "NEIGHBOR" | "OTHER";
+            /** Format: date */
+            fromDate?: string;
+            /** @enum {string} */
+            fromDatePrecision?: "DAY" | "MONTH" | "SEASON" | "YEAR" | "RANGE" | "APPROX" | "UNKNOWN";
+            /** Format: date */
+            toDate?: string;
+            /** @enum {string} */
+            toDatePrecision?: "DAY" | "MONTH" | "SEASON" | "YEAR" | "RANGE" | "APPROX" | "UNKNOWN";
+            notes?: string;
+        };
+        RelationshipDTO: {
+            /** Format: uuid */
+            id: string;
+            /** Format: uuid */
+            personId: string;
+            /** Format: uuid */
+            relatedPersonId: string;
+            personDisplayName: string;
+            /** Format: int32 */
+            personBirthYear?: number;
+            /** Format: int32 */
+            personDeathYear?: number;
+            relatedPersonDisplayName: string;
+            /** Format: int32 */
+            relatedPersonBirthYear?: number;
+            /** Format: int32 */
+            relatedPersonDeathYear?: number;
+            /** @enum {string} */
+            relationType: "PARENT_OF" | "SPOUSE_OF" | "SIBLING_OF" | "FRIEND" | "COLLEAGUE" | "EMPLOYER" | "DOCTOR" | "NEIGHBOR" | "OTHER";
+            /** Format: date */
+            fromDate?: string;
+            /** @enum {string} */
+            fromDatePrecision: "DAY" | "MONTH" | "SEASON" | "YEAR" | "RANGE" | "APPROX" | "UNKNOWN";
+            /** Format: date */
+            toDate?: string;
+            /** @enum {string} */
+            toDatePrecision: "DAY" | "MONTH" | "SEASON" | "YEAR" | "RANGE" | "APPROX" | "UNKNOWN";
+            notes?: string;
+        };
         JourneyReorderDTO: {
             itemIds?: string[];
         };
@@ -2008,42 +2052,6 @@ export interface components {
             /** Format: uuid */
             targetId: string;
         };
-        CreateRelationshipRequest: {
-            /** Format: uuid */
-            relatedPersonId: string;
-            /** @enum {string} */
-            relationType: "PARENT_OF" | "SPOUSE_OF" | "SIBLING_OF" | "FRIEND" | "COLLEAGUE" | "EMPLOYER" | "DOCTOR" | "NEIGHBOR" | "OTHER";
-            /** Format: int32 */
-            fromYear?: number;
-            /** Format: int32 */
-            toYear?: number;
-            notes?: string;
-        };
-        RelationshipDTO: {
-            /** Format: uuid */
-            id: string;
-            /** Format: uuid */
-            personId: string;
-            /** Format: uuid */
-            relatedPersonId: string;
-            personDisplayName: string;
-            /** Format: int32 */
-            personBirthYear?: number;
-            /** Format: int32 */
-            personDeathYear?: number;
-            relatedPersonDisplayName: string;
-            /** Format: int32 */
-            relatedPersonBirthYear?: number;
-            /** Format: int32 */
-            relatedPersonDeathYear?: number;
-            /** @enum {string} */
-            relationType: "PARENT_OF" | "SPOUSE_OF" | "SIBLING_OF" | "FRIEND" | "COLLEAGUE" | "EMPLOYER" | "DOCTOR" | "NEIGHBOR" | "OTHER";
-            /** Format: int32 */
-            fromYear?: number;
-            /** Format: int32 */
-            toYear?: number;
-            notes?: string;
-        };
         PersonNameAliasDTO: {
             lastName: string;
             firstName?: string;
@@ -2459,6 +2467,8 @@ export interface components {
             rootTagId?: string;
             rootTagName?: string;
             rootTagColor?: string;
+            /** Format: uuid */
+            linkedEventId?: string;
         };
         TimelineYearDTO: {
             /** Format: int32 */
@@ -3200,6 +3210,54 @@ export interface operations {
             };
         };
     };
+    updateRelationship: {
+        parameters: {
+            query?: never;
+            header?: never;
+            path: {
+                id: string;
+                relId: string;
+            };
+            cookie?: never;
+        };
+        requestBody: {
+            content: {
+                "application/json": components["schemas"]["RelationshipUpsertRequest"];
+            };
+        };
+        responses: {
+            /** @description OK */
+            200: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "*/*": components["schemas"]["RelationshipDTO"];
+                };
+            };
+        };
+    };
+    deleteRelationship: {
+        parameters: {
+            query?: never;
+            header?: never;
+            path: {
+                id: string;
+                relId: string;
+            };
+            cookie?: never;
+        };
+        requestBody?: never;
+        responses: {
+            /** @description No Content */
+            204: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content?: never;
+            };
+        };
+    };
     reorderItems: {
         parameters: {
             query?: never;
@@ -3663,7 +3721,7 @@ export interface operations {
         };
         requestBody: {
             content: {
-                "application/json": components["schemas"]["CreateRelationshipRequest"];
+                "application/json": components["schemas"]["RelationshipUpsertRequest"];
             };
         };
         responses: {
@@ -5909,27 +5967,6 @@ export interface operations {
             };
         };
     };
-    deleteRelationship: {
-        parameters: {
-            query?: never;
-            header?: never;
-            path: {
-                id: string;
-                relId: string;
-            };
-            cookie?: never;
-        };
-        requestBody?: never;
-        responses: {
-            /** @description No Content */
-            204: {
-                headers: {
-                    [name: string]: unknown;
-                };
-                content?: never;
-            };
-        };
-    };
     removeAlias: {
         parameters: {
             query?: never;

frontend/src/lib/messages.spec.ts

@@ -98,4 +98,68 @@ describe('message key parity', () => {
 		expect(en).toMatchObject({ timeline_tag_chip_label: 'Topic' });
 		expect(es).toMatchObject({ timeline_tag_chip_label: 'Tema' });
 	});
+
+	// #780 REQ-010: the layer-filter strings are Paraglide keys in every locale.
+	// timeline_filter_trigger (0 active) and timeline_filter_trigger_active ({count},
+	// ≥1 active) are distinct keys so the trigger never reads "Filter (0 aktiv)".
+	it('zeitstrahl layer-filter keys are present in all locales (#780 REQ-010)', () => {
+		const requiredKeys = [
+			'timeline_filter_label_layers',
+			'timeline_filter_layer_personal',
+			'timeline_filter_layer_historical',
+			'timeline_filter_layer_letters',
+			'timeline_filter_trigger',
+			'timeline_filter_trigger_active',
+			'timeline_filter_reset',
+			'timeline_filter_empty_state'
+		];
+		for (const key of requiredKeys) {
+			expect(de, `missing key in de: ${key}`).toHaveProperty(key);
+			expect(en, `missing key in en: ${key}`).toHaveProperty(key);
+			expect(es, `missing key in es: ${key}`).toHaveProperty(key);
+		}
+		// the active-count key carries the established {count} placeholder
+		expect(de.timeline_filter_trigger_active).toContain('{count}');
+		expect(en.timeline_filter_trigger_active).toContain('{count}');
+		expect(es.timeline_filter_trigger_active).toContain('{count}');
+	});
+
+	// #842: the two curator-affordance CTA labels (Zeitstrahl header + person page)
+	// are Paraglide keys present in every locale; the edit pencils reuse btn_edit.
+	it('curator-affordance CTA keys are present in all locales (#842)', () => {
+		for (const key of ['timeline_add_event', 'person_add_event']) {
+			expect(de, `missing key in de: ${key}`).toHaveProperty(key);
+			expect(en, `missing key in en: ${key}`).toHaveProperty(key);
+			expect(es, `missing key in es: ${key}`).toHaveProperty(key);
+		}
+	});
+
+	// #827 REQ-012: the grouping toggle + bucket strings are new Paraglide keys in
+	// every locale; the pre-existing timeline_grouping_date / timeline_tag_chip_label /
+	// timeline_filter_* set is reused, never re-added.
+	it('zeitstrahl grouping + bucket keys are present in all locales (#827 REQ-012)', () => {
+		const requiredKeys = [
+			'timeline_grouping_event',
+			'timeline_grouping_thema',
+			'timeline_grouping_aria_label',
+			'timeline_grouping_segment_date',
+			'timeline_grouping_segment_event',
+			'timeline_grouping_segment_thema',
+			'timeline_grouping_segment_date_short',
+			'timeline_grouping_segment_event_short',
+			'timeline_grouping_segment_thema_short',
+			'timeline_grouping_disabled_reason',
+			'timeline_grouping_multitag_hint',
+			'timeline_bucket_other_letters',
+			'timeline_bucket_no_topic'
+		];
+		for (const key of requiredKeys) {
+			expect(de, `missing key in de: ${key}`).toHaveProperty(key);
+			expect(en, `missing key in en: ${key}`).toHaveProperty(key);
+			expect(es, `missing key in es: ${key}`).toHaveProperty(key);
+		}
+		// the pre-existing meta-line + chip keys are reused by #827, not re-declared
+		expect(de).toHaveProperty('timeline_grouping_date');
+		expect(de).toHaveProperty('timeline_tag_chip_label');
+	});
 });

frontend/src/lib/person/PersonHoverCard.svelte.spec.ts

@@ -193,7 +193,9 @@ describe('PersonHoverCard — loaded state', () => {
 				relatedPersonId: 'p-spouse',
 				personDisplayName: 'Auguste',
 				relatedPersonDisplayName: 'Otto Raddatz',
-				relationType: 'SPOUSE_OF'
+				relationType: 'SPOUSE_OF',
+				fromDatePrecision: 'UNKNOWN',
+				toDatePrecision: 'UNKNOWN'
 			},
 			{
 				id: 'r2',
@@ -201,7 +203,9 @@ describe('PersonHoverCard — loaded state', () => {
 				relatedPersonId: 'p-friend',
 				personDisplayName: 'Auguste',
 				relatedPersonDisplayName: 'Karl Friend',
-				relationType: 'FRIEND'
+				relationType: 'FRIEND',
+				fromDatePrecision: 'UNKNOWN',
+				toDatePrecision: 'UNKNOWN'
 			},
 			{
 				id: 'r3',
@@ -209,7 +213,9 @@ describe('PersonHoverCard — loaded state', () => {
 				relatedPersonId: 'p-sibling',
 				personDisplayName: 'Auguste',
 				relatedPersonDisplayName: 'Marie Sister',
-				relationType: 'SIBLING_OF'
+				relationType: 'SIBLING_OF',
+				fromDatePrecision: 'UNKNOWN',
+				toDatePrecision: 'UNKNOWN'
 			}
 		];
 		render(PersonHoverCard, {
@@ -235,7 +241,9 @@ describe('PersonHoverCard — loaded state', () => {
 				relatedPersonId: 'p-aug',
 				personDisplayName: 'Heinrich Raddatz',
 				relatedPersonDisplayName: 'Auguste Raddatz',
-				relationType: 'PARENT_OF'
+				relationType: 'PARENT_OF',
+				fromDatePrecision: 'UNKNOWN',
+				toDatePrecision: 'UNKNOWN'
 			}
 		];
 		render(PersonHoverCard, {
@@ -258,7 +266,9 @@ describe('PersonHoverCard — loaded state', () => {
 				relatedPersonId: 'p-friend',
 				personDisplayName: 'Auguste',
 				relatedPersonDisplayName: 'Karl Friend',
-				relationType: 'FRIEND'
+				relationType: 'FRIEND',
+				fromDatePrecision: 'UNKNOWN',
+				toDatePrecision: 'UNKNOWN'
 			}
 		];
 		render(PersonHoverCard, {

frontend/src/lib/person/PersonLifeDateField.svelte

@@ -1,17 +1,10 @@
 <script lang="ts">
-import { onMount } from 'svelte';
 import { m } from '$lib/paraglide/messages.js';
-import DateInput from '$lib/shared/primitives/DateInput.svelte';
+import DateInputWithPrecision from '$lib/shared/primitives/DateInputWithPrecision.svelte';
 import type { DatePrecision } from '$lib/shared/utils/documentDate';
 
 // Only DAY / MONTH / YEAR are offered for life dates: RANGE and SEASON make no
 // sense for a birth or death, and APPROX stays display-only for legacy imports (#773).
-const PERSON_DATE_PRECISIONS: { value: DatePrecision; label: () => string }[] = [
-	{ value: 'DAY', label: m.person_precision_day },
-	{ value: 'MONTH', label: m.person_precision_month },
-	{ value: 'YEAR', label: m.person_precision_year }
-];
-
 let {
 	name,
 	legend,
@@ -26,73 +19,21 @@ let {
 	initialPrecision?: string | null;
 } = $props();
 
-let iso = $state('');
+const precisions: { value: DatePrecision; label: string }[] = $derived([
-let errorMessage = $state<string | null>(null);
+	{ value: 'DAY', label: m.person_precision_day() },
-let inputEl = $state<HTMLInputElement | undefined>();
+	{ value: 'MONTH', label: m.person_precision_month() },
-let precision = $state<DatePrecision>('DAY');
+	{ value: 'YEAR', label: m.person_precision_year() }
-
+]);
-// Seed once at mount (WhoWhenSection pattern): a later load() rerun must not
+const hint = $derived(`${m.person_precision_hint()} · ${m.person_date_placeholder_hint()}`);
-// stomp the user's in-progress edit.
-onMount(() => {
-	if (initialIso) {
-		iso = initialIso;
-	}
-	const offered = PERSON_DATE_PRECISIONS.some((p) => p.value === initialPrecision);
-	if (offered) {
-		precision = initialPrecision as DatePrecision;
-	} else if (initialIso) {
-		// Legacy APPROX/SEASON/RANGE precision is not editable here — seed YEAR so an
-		// untouched save does not silently claim DAY precision for the stored date.
-		precision = 'YEAR';
-	}
-});
-
-// A partial date leaves the hidden ISO empty — submitting then would silently
-// clear a stored date. Block native submission until completed or fully emptied.
-$effect(() => {
-	inputEl?.setCustomValidity(errorMessage ?? '');
-});
-
-const controlCls =
-	'block min-h-[44px] w-full rounded border border-line px-3 py-2 font-serif text-ink focus:outline-none focus-visible:ring-2 focus-visible:ring-focus-ring';
 </script>
 
-<fieldset>
+<DateInputWithPrecision
-	<legend class="mb-1 block text-xs font-bold tracking-widest text-ink-3 uppercase">
-		{legend}
-	</legend>
-	<div class="flex flex-col gap-2 sm:flex-row">
-		<div class="flex-1">
-			<DateInput
-				bind:value={iso}
-				bind:errorMessage={errorMessage}
-				bind:inputEl={inputEl}
 	name={name}
-				id={name}
+	legend={legend}
-				placeholder="TT.MM.JJJJ"
+	precisionLabel={precisionLabel}
-				ariaLabel={legend}
+	precisions={precisions}
-				ariaDescribedby={errorMessage ? `${name}-error` : undefined}
+	hint={hint}
-				class={controlCls}
+	initialIso={initialIso}
-			/>
+	initialPrecision={initialPrecision}
-			{#if errorMessage}
+	selectClass="bg-surface"
-				<p id="{name}-error" class="mt-1 font-sans text-xs text-red-600">{errorMessage}</p>
+/>
-			{/if}
-		</div>
-		<div class="flex-1">
-			<select
-				id="{name}Precision"
-				name="{name}Precision"
-				aria-label="{legend}: {precisionLabel}"
-				bind:value={precision}
-				class="{controlCls} bg-surface"
-			>
-				{#each PERSON_DATE_PRECISIONS as p (p.value)}
-					<option value={p.value}>{p.label()}</option>
-				{/each}
-			</select>
-		</div>
-	</div>
-	<p class="mt-1 font-sans text-xs text-ink-3">
-		{m.person_precision_hint()} · {m.person_date_placeholder_hint()}
-	</p>
-</fieldset>

frontend/src/lib/person/genealogy/StammbaumCard.svelte

@@ -4,6 +4,7 @@ import { m } from '$lib/paraglide/messages.js';
 import RelationshipChip from '$lib/person/relationship/RelationshipChip.svelte';
 import AddRelationshipForm from '$lib/person/relationship/AddRelationshipForm.svelte';
 import { chipLabel, otherName, inferredRelationshipLabel } from '$lib/person/relationshipLabels';
+import { formatRelationshipDateRange } from '$lib/person/relationshipDates';
 import type { components } from '$lib/generated/api';
 
 type RelationshipDTO = components['schemas']['RelationshipDTO'];
@@ -29,13 +30,15 @@ let {
 
 type RelationType = NonNullable<RelationshipDTO['relationType']>;
 
-const sortedDirect = $derived([...relationships].sort(byTypeThenYear));
+const sortedDirect = $derived([...relationships].sort(byTypeThenDate));
 const topDerived = $derived(inferredRelationships.slice(0, 5));
+let editingRelId = $state<string | null>(null);
 
-function byTypeThenYear(a: RelationshipDTO, b: RelationshipDTO): number {
+function byTypeThenDate(a: RelationshipDTO, b: RelationshipDTO): number {
 	const order = relationTypeOrder(a.relationType) - relationTypeOrder(b.relationType);
 	if (order !== 0) return order;
-	return (a.fromYear ?? 0) - (b.fromYear ?? 0);
+	// ISO dates sort lexicographically == chronologically; a missing date sorts first.
+	return (a.fromDate ?? '').localeCompare(b.fromDate ?? '');
 }
 
 function relationTypeOrder(t: RelationType | undefined): number {
@@ -53,13 +56,13 @@ function relationTypeOrder(t: RelationType | undefined): number {
 	return order[t ?? 'OTHER'] ?? 99;
 }
 
-function yearRange(rel: RelationshipDTO): string {
+function dateRangeOf(rel: RelationshipDTO): string {
-	const from = rel.fromYear;
+	return formatRelationshipDateRange(
-	const to = rel.toYear;
+		rel.fromDate,
-	if (from && to) return `${from}–${to}`;
+		rel.fromDatePrecision,
-	if (from) return m.relation_year_from({ year: from });
+		rel.toDate,
-	if (to) return m.relation_year_to({ year: to });
+		rel.toDatePrecision
-	return '';
+	);
 }
 </script>
 
@@ -132,10 +135,20 @@ function yearRange(rel: RelationshipDTO): string {
 				<RelationshipChip
 					chipLabel={chipLabel(rel, personId)}
 					otherName={otherName(rel, personId)}
-					yearRange={yearRange(rel)}
+					dateRange={dateRangeOf(rel)}
 					canWrite={canWrite}
 					relId={rel.id}
+					onEdit={canWrite ? () => (editingRelId = rel.id) : undefined}
 				/>
+				{#if editingRelId === rel.id}
+					<li>
+						<AddRelationshipForm
+							personId={personId}
+							relationship={rel}
+							onClose={() => (editingRelId = null)}
+						/>
+					</li>
+				{/if}
 			{/each}
 		</ul>
 	{/if}

frontend/src/lib/person/genealogy/StammbaumCard.svelte.test.ts

@@ -111,17 +111,21 @@ describe('StammbaumCard', () => {
 		expect(items.length).toBeGreaterThanOrEqual(2);
 	});
 
-	it('renders the year range "from–to" for a relationship with both years', async () => {
+	it('renders the date range "from – to" for a relationship with both dates', async () => {
 		render(StammbaumCard, {
 			props: baseProps({
 				relationships: [
 					{
 						id: 'r-1',
+						personId: 'p-1',
+						relatedPersonId: 'p-x',
+						personDisplayName: 'Anna',
+						relatedPersonDisplayName: 'Xavier',
 						relationType: 'COLLEAGUE',
-						fromYear: 1940,
+						fromDate: '1940-01-01',
-						toYear: 1945,
+						fromDatePrecision: 'YEAR',
-						personA: { id: 'p-1', displayName: 'Anna' },
+						toDate: '1945-01-01',
-						personB: { id: 'p-x', displayName: 'Xavier' }
+						toDatePrecision: 'YEAR'
 					}
 				]
 			})
@@ -131,23 +135,27 @@ describe('StammbaumCard', () => {
 		expect(document.body.textContent).toContain('1945');
 	});
 
-	it('renders only "fromYear" for a relationship with no end year', async () => {
+	it('renders only the start date for a relationship with no end date', async () => {
 		render(StammbaumCard, {
 			props: baseProps({
 				relationships: [
 					{
 						id: 'r-2',
+						personId: 'p-1',
+						relatedPersonId: 'p-y',
+						personDisplayName: 'Anna',
+						relatedPersonDisplayName: 'Yvonne',
 						relationType: 'NEIGHBOR',
-						fromYear: 1935,
+						fromDate: '1935-01-01',
-						personA: { id: 'p-1', displayName: 'Anna' },
+						fromDatePrecision: 'YEAR',
-						personB: { id: 'p-y', displayName: 'Yvonne' }
+						toDatePrecision: 'UNKNOWN'
 					}
 				]
 			})
 		});
 
 		expect(document.body.textContent).toContain('1935');
-		expect(document.body.textContent).not.toContain('1935–');
+		expect(document.body.textContent).not.toContain('1935 –');
 	});
 
 	it('renders the inferred-relationships disclosure when topDerived has items', async () => {

frontend/src/lib/person/genealogy/StammbaumConnectors.svelte

@@ -250,7 +250,7 @@ const parentLinks = $derived.by<ParentLinks>(() => {
 				y2={bCenter.y}
 				stroke="var(--c-primary)"
 				stroke-width="1.5"
-				stroke-dasharray={e.toYear ? '4 4' : undefined}
+				stroke-dasharray={e.toDate ? '4 4' : undefined}
 			/>
 			<circle
 				cx={(aCenter.x + bCenter.x) / 2}

frontend/src/lib/person/genealogy/StammbaumConnectors.svelte.test.ts

@@ -18,7 +18,9 @@ function parentEdge(parentId: string, childId: string): RelationshipDTO {
 		relatedPersonId: childId,
 		personDisplayName: '',
 		relatedPersonDisplayName: '',
-		relationType: 'PARENT_OF'
+		relationType: 'PARENT_OF',
+		fromDatePrecision: 'UNKNOWN',
+		toDatePrecision: 'UNKNOWN'
 	};
 }
 
@@ -30,7 +32,9 @@ function endedSpouseEdge(a: string, b: string): RelationshipDTO {
 		personDisplayName: '',
 		relatedPersonDisplayName: '',
 		relationType: 'SPOUSE_OF',
-		toYear: 1950
+		fromDatePrecision: 'UNKNOWN',
+		toDate: '1950-01-01',
+		toDatePrecision: 'YEAR'
 	};
 }
 

frontend/src/lib/person/genealogy/StammbaumSidePanel.svelte

@@ -54,12 +54,19 @@ async function loadFor(id: string) {
 }
 
 async function handleAddRelationship(data: RelFormData) {
-	const body: Record<string, string | number> = {
+	const body: Record<string, string> = {
 		relatedPersonId: data.relatedPersonId,
 		relationType: data.relationType
 	};
-	if (data.fromYear !== undefined) body.fromYear = data.fromYear;
+	if (data.fromDate) {
-	if (data.toYear !== undefined) body.toYear = data.toYear;
+		body.fromDate = data.fromDate;
+		if (data.fromDatePrecision) body.fromDatePrecision = data.fromDatePrecision;
+	}
+	if (data.toDate) {
+		body.toDate = data.toDate;
+		if (data.toDatePrecision) body.toDatePrecision = data.toDatePrecision;
+	}
+	if (data.notes) body.notes = data.notes;
 	const res = await csrfFetch(`/api/persons/${node.id}/relationships`, {
 		method: 'POST',
 		headers: { 'Content-Type': 'application/json' },

frontend/src/lib/person/genealogy/StammbaumSidePanel.svelte.spec.ts

@@ -72,20 +72,20 @@ describe('StammbaumSidePanel', () => {
 		await expect.element(page.getByText('Noch keine Beziehungen bekannt.')).toBeInTheDocument();
 	});
 
-	it('year inputs inside the add form have label elements (canWrite=true)', async () => {
+	it('date inputs inside the add form have accessible labels (canWrite=true)', async () => {
 		render(StammbaumSidePanel, { node: makeNode(), onClose: vi.fn(), canWrite: true });
 		await expect.element(page.getByText('Noch keine Beziehungen bekannt.')).toBeInTheDocument();
 		const addBtn = [...document.querySelectorAll<HTMLButtonElement>('button')].find((b) =>
 			/Beziehung hinzufügen/i.test(b.textContent ?? '')
 		);
 		addBtn!.click();
-		await expect.element(page.getByRole('combobox')).toBeInTheDocument();
+		await expect.element(page.getByRole('combobox', { name: 'Typ' })).toBeInTheDocument();
-		const yearInputs = [...document.querySelectorAll('input')].filter(
+		const dateInputs = [...document.querySelectorAll('input')].filter(
 			(i) => i.inputMode === 'numeric'
 		);
-		expect(yearInputs.length).toBeGreaterThan(0);
+		expect(dateInputs.length).toBeGreaterThan(0);
-		for (const input of yearInputs) {
+		for (const input of dateInputs) {
-			expect(input.closest('label')).not.toBeNull();
+			expect(input.getAttribute('aria-label')).toBeTruthy();
 		}
 	});
 

frontend/src/lib/person/genealogy/StammbaumTree.svelte.test.ts

@@ -3,6 +3,9 @@ import { render } from 'vitest-browser-svelte';
 import StammbaumTree from './StammbaumTree.svelte';
 import type { PanZoomState } from './panZoom';
 import { DIMMED_OPACITY } from './layout/highlightLineage';
+import type { components } from '$lib/generated/api';
+
+type RelationshipDTO = components['schemas']['RelationshipDTO'];
 
 const ID_A = '00000000-0000-0000-0000-000000000001';
 const ID_B = '00000000-0000-0000-0000-000000000002';
@@ -105,7 +108,9 @@ describe('StammbaumTree viewBox', () => {
 					relatedPersonId: PARENT_B,
 					personDisplayName: 'Walter',
 					relatedPersonDisplayName: 'Eugenie',
-					relationType: 'SPOUSE_OF'
+					relationType: 'SPOUSE_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				},
 				{
 					id: 'p1a',
@@ -113,7 +118,9 @@ describe('StammbaumTree viewBox', () => {
 					relatedPersonId: CHILD_1,
 					personDisplayName: 'Walter',
 					relatedPersonDisplayName: 'Clara',
-					relationType: 'PARENT_OF'
+					relationType: 'PARENT_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				},
 				{
 					id: 'p1b',
@@ -121,7 +128,9 @@ describe('StammbaumTree viewBox', () => {
 					relatedPersonId: CHILD_1,
 					personDisplayName: 'Eugenie',
 					relatedPersonDisplayName: 'Clara',
-					relationType: 'PARENT_OF'
+					relationType: 'PARENT_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				},
 				{
 					id: 'p2a',
@@ -129,7 +138,9 @@ describe('StammbaumTree viewBox', () => {
 					relatedPersonId: CHILD_2,
 					personDisplayName: 'Walter',
 					relatedPersonDisplayName: 'Hans',
-					relationType: 'PARENT_OF'
+					relationType: 'PARENT_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				},
 				{
 					id: 'p2b',
@@ -137,7 +148,9 @@ describe('StammbaumTree viewBox', () => {
 					relatedPersonId: CHILD_2,
 					personDisplayName: 'Eugenie',
 					relatedPersonDisplayName: 'Hans',
-					relationType: 'PARENT_OF'
+					relationType: 'PARENT_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				}
 			],
 			selectedId: null,
@@ -181,7 +194,9 @@ describe('StammbaumTree viewBox', () => {
 					relatedPersonId: PARENT_B,
 					personDisplayName: 'Walter',
 					relatedPersonDisplayName: 'Eugenie',
-					relationType: 'SPOUSE_OF'
+					relationType: 'SPOUSE_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				},
 				{
 					id: 'p1',
@@ -189,7 +204,9 @@ describe('StammbaumTree viewBox', () => {
 					relatedPersonId: CHILD,
 					personDisplayName: 'Walter',
 					relatedPersonDisplayName: 'Hans',
-					relationType: 'PARENT_OF'
+					relationType: 'PARENT_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				},
 				{
 					id: 'p2',
@@ -197,7 +214,9 @@ describe('StammbaumTree viewBox', () => {
 					relatedPersonId: CHILD,
 					personDisplayName: 'Eugenie',
 					relatedPersonDisplayName: 'Hans',
-					relationType: 'PARENT_OF'
+					relationType: 'PARENT_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				}
 			],
 			selectedId: null,
@@ -244,7 +263,9 @@ describe('StammbaumTree viewBox', () => {
 					relatedPersonId: EUGENIE,
 					personDisplayName: 'Walter',
 					relatedPersonDisplayName: 'Eugenie',
-					relationType: 'SPOUSE_OF'
+					relationType: 'SPOUSE_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				},
 				{
 					id: 'p1',
@@ -252,7 +273,9 @@ describe('StammbaumTree viewBox', () => {
 					relatedPersonId: HANS,
 					personDisplayName: 'Walter',
 					relatedPersonDisplayName: 'Hans',
-					relationType: 'PARENT_OF'
+					relationType: 'PARENT_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				},
 				{
 					id: 'p2',
@@ -260,7 +283,9 @@ describe('StammbaumTree viewBox', () => {
 					relatedPersonId: HANS,
 					personDisplayName: 'Eugenie',
 					relatedPersonDisplayName: 'Hans',
-					relationType: 'PARENT_OF'
+					relationType: 'PARENT_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				},
 				{
 					id: 'p3',
@@ -268,7 +293,9 @@ describe('StammbaumTree viewBox', () => {
 					relatedPersonId: CLARA,
 					personDisplayName: 'Walter',
 					relatedPersonDisplayName: 'Clara',
-					relationType: 'PARENT_OF'
+					relationType: 'PARENT_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				},
 				{
 					id: 'p4',
@@ -276,7 +303,9 @@ describe('StammbaumTree viewBox', () => {
 					relatedPersonId: CLARA,
 					personDisplayName: 'Eugenie',
 					relatedPersonDisplayName: 'Clara',
-					relationType: 'PARENT_OF'
+					relationType: 'PARENT_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				},
 				{
 					id: 's2',
@@ -284,7 +313,9 @@ describe('StammbaumTree viewBox', () => {
 					relatedPersonId: HILDE,
 					personDisplayName: 'Hans',
 					relatedPersonDisplayName: 'Hilde',
-					relationType: 'SPOUSE_OF'
+					relationType: 'SPOUSE_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				},
 				{
 					id: 'p5',
@@ -292,7 +323,9 @@ describe('StammbaumTree viewBox', () => {
 					relatedPersonId: LILI,
 					personDisplayName: 'Hans',
 					relatedPersonDisplayName: 'Lili',
-					relationType: 'PARENT_OF'
+					relationType: 'PARENT_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				},
 				{
 					id: 'p6',
@@ -300,7 +333,9 @@ describe('StammbaumTree viewBox', () => {
 					relatedPersonId: LILI,
 					personDisplayName: 'Hilde',
 					relatedPersonDisplayName: 'Lili',
-					relationType: 'PARENT_OF'
+					relationType: 'PARENT_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				}
 			],
 			selectedId: null,
@@ -358,7 +393,9 @@ describe('StammbaumTree viewBox', () => {
 					relatedPersonId: ID_B,
 					personDisplayName: 'Anna',
 					relatedPersonDisplayName: 'Bertha',
-					relationType: 'SPOUSE_OF'
+					relationType: 'SPOUSE_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				}
 			],
 			selectedId: null,
@@ -391,7 +428,9 @@ describe('StammbaumTree viewBox', () => {
 					relatedPersonId: ID_B,
 					personDisplayName: 'Anna',
 					relatedPersonDisplayName: 'Bertha',
-					relationType: 'SPOUSE_OF'
+					relationType: 'SPOUSE_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				}
 			],
 			selectedId: null,
@@ -599,7 +638,9 @@ describe('StammbaumTree keyboard pan/zoom (#692)', () => {
 					relatedPersonId: ID_B,
 					personDisplayName: 'Anna',
 					relatedPersonDisplayName: 'Bertha',
-					relationType: 'SPOUSE_OF'
+					relationType: 'SPOUSE_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				}
 			],
 			selectedId: null,
@@ -668,7 +709,9 @@ describe('StammbaumTree keyboard pan/zoom (#692)', () => {
 					personDisplayName: 'Anna',
 					relatedPersonDisplayName: 'Bertha',
 					relationType: 'SPOUSE_OF',
-					toYear: 1925
+					fromDatePrecision: 'UNKNOWN',
+					toDate: '1925-01-01',
+					toDatePrecision: 'YEAR'
 				}
 			],
 			selectedId: null,
@@ -695,7 +738,9 @@ describe('StammbaumTree keyboard pan/zoom (#692)', () => {
 					relatedPersonId: ID_B,
 					personDisplayName: 'Anna',
 					relatedPersonDisplayName: 'Bertha',
-					relationType: 'SPOUSE_OF'
+					relationType: 'SPOUSE_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				}
 			],
 			selectedId: null,
@@ -723,7 +768,9 @@ describe('StammbaumTree keyboard pan/zoom (#692)', () => {
 					relatedPersonId: CHILD,
 					personDisplayName: 'Parent',
 					relatedPersonDisplayName: 'Child',
-					relationType: 'PARENT_OF'
+					relationType: 'PARENT_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				}
 			],
 			selectedId: null,
@@ -908,6 +955,8 @@ describe('StammbaumTree lineage highlight (#703)', () => {
 		personDisplayName: string;
 		relatedPersonDisplayName: string;
 		relationType: 'PARENT_OF' | 'SPOUSE_OF';
+		fromDatePrecision: 'UNKNOWN';
+		toDatePrecision: 'UNKNOWN';
 	};
 	const edge = (
 		personId: string,
@@ -919,7 +968,9 @@ describe('StammbaumTree lineage highlight (#703)', () => {
 		relatedPersonId,
 		personDisplayName: '',
 		relatedPersonDisplayName: '',
-		relationType
+		relationType,
+		fromDatePrecision: 'UNKNOWN',
+		toDatePrecision: 'UNKNOWN'
 	});
 
 	const NODES = [
@@ -1104,14 +1155,16 @@ describe('StammbaumTree keyboard tab order (#718)', () => {
 	// year, then a deterministic id tie-break), not alphabetically — with no birth
 	// years here Walter (id …a1) owns the run and Eugenie sits to his right. So the
 	// deterministic visual order is Walter, Eugenie (top row) then Clara, Hans.
-	const FAMILY_EDGES = [
+	const FAMILY_EDGES: RelationshipDTO[] = [
 		{
 			id: 'sp',
 			personId: WALTER,
 			relatedPersonId: EUGENIE,
 			personDisplayName: 'Walter',
 			relatedPersonDisplayName: 'Eugenie',
-			relationType: 'SPOUSE_OF'
+			relationType: 'SPOUSE_OF',
+			fromDatePrecision: 'UNKNOWN',
+			toDatePrecision: 'UNKNOWN'
 		},
 		{
 			id: 'p1',
@@ -1119,7 +1172,9 @@ describe('StammbaumTree keyboard tab order (#718)', () => {
 			relatedPersonId: CLARA,
 			personDisplayName: 'Walter',
 			relatedPersonDisplayName: 'Clara',
-			relationType: 'PARENT_OF'
+			relationType: 'PARENT_OF',
+			fromDatePrecision: 'UNKNOWN',
+			toDatePrecision: 'UNKNOWN'
 		},
 		{
 			id: 'p2',
@@ -1127,7 +1182,9 @@ describe('StammbaumTree keyboard tab order (#718)', () => {
 			relatedPersonId: CLARA,
 			personDisplayName: 'Eugenie',
 			relatedPersonDisplayName: 'Clara',
-			relationType: 'PARENT_OF'
+			relationType: 'PARENT_OF',
+			fromDatePrecision: 'UNKNOWN',
+			toDatePrecision: 'UNKNOWN'
 		},
 		{
 			id: 'p3',
@@ -1135,7 +1192,9 @@ describe('StammbaumTree keyboard tab order (#718)', () => {
 			relatedPersonId: HANS,
 			personDisplayName: 'Walter',
 			relatedPersonDisplayName: 'Hans',
-			relationType: 'PARENT_OF'
+			relationType: 'PARENT_OF',
+			fromDatePrecision: 'UNKNOWN',
+			toDatePrecision: 'UNKNOWN'
 		},
 		{
 			id: 'p4',
@@ -1143,7 +1202,9 @@ describe('StammbaumTree keyboard tab order (#718)', () => {
 			relatedPersonId: HANS,
 			personDisplayName: 'Eugenie',
 			relatedPersonDisplayName: 'Hans',
-			relationType: 'PARENT_OF'
+			relationType: 'PARENT_OF',
+			fromDatePrecision: 'UNKNOWN',
+			toDatePrecision: 'UNKNOWN'
 		}
 	];
 

frontend/src/lib/person/genealogy/layout/buildLayout.test.ts

@@ -42,7 +42,9 @@ function parentEdge(parentId: string, childId: string, id = parentId + childId):
 		relatedPersonId: childId,
 		personDisplayName: '',
 		relatedPersonDisplayName: '',
-		relationType: 'PARENT_OF'
+		relationType: 'PARENT_OF',
+		fromDatePrecision: 'UNKNOWN',
+		toDatePrecision: 'UNKNOWN'
 	};
 }
 
@@ -53,7 +55,9 @@ function spouseEdge(a: string, b: string, id = a + b): RelationshipDTO {
 		relatedPersonId: b,
 		personDisplayName: '',
 		relatedPersonDisplayName: '',
-		relationType: 'SPOUSE_OF'
+		relationType: 'SPOUSE_OF',
+		fromDatePrecision: 'UNKNOWN',
+		toDatePrecision: 'UNKNOWN'
 	};
 }
 
@@ -220,7 +224,10 @@ describe('buildLayout — multi-spouse ordering (#361)', () => {
 		fromYear: number | undefined,
 		id = a + b
 	): RelationshipDTO {
-		return { ...spouseEdge(a, b, id), fromYear };
+		return {
+			...spouseEdge(a, b, id),
+			...(fromYear != null ? { fromDate: `${fromYear}-01-01`, fromDatePrecision: 'YEAR' } : {})
+		};
 	}
 
 	it('multi_spouses_ordered_by_fromYear_then_displayName', () => {
@@ -329,7 +336,7 @@ describe('buildLayout — multi-spouse ordering (#361)', () => {
 		// fail fast instead so the maintainer either updates the test or
 		// splits into a year-branch / name-branch pair.
 		const spouseEdgesWithYear = fixtureEdges.filter(
-			(e) => e.relationType === 'SPOUSE_OF' && e.fromYear != null
+			(e) => e.relationType === 'SPOUSE_OF' && e.fromDate != null
 		);
 		expect(
 			spouseEdgesWithYear,

frontend/src/lib/person/genealogy/layout/familyForest.test.ts

@@ -21,7 +21,9 @@ function parent(p: string, c: string): RelationshipDTO {
 		relatedPersonId: c,
 		personDisplayName: '',
 		relatedPersonDisplayName: '',
-		relationType: 'PARENT_OF'
+		relationType: 'PARENT_OF',
+		fromDatePrecision: 'UNKNOWN',
+		toDatePrecision: 'UNKNOWN'
 	};
 }
 
@@ -33,7 +35,9 @@ function spouse(a: string, b: string, fromYear?: number): RelationshipDTO {
 		personDisplayName: '',
 		relatedPersonDisplayName: '',
 		relationType: 'SPOUSE_OF',
-		...(fromYear != null ? { fromYear } : {})
+		fromDatePrecision: 'UNKNOWN',
+		toDatePrecision: 'UNKNOWN',
+		...(fromYear != null ? { fromDate: `${fromYear}-01-01`, fromDatePrecision: 'YEAR' } : {})
 	};
 }
 

frontend/src/lib/person/genealogy/layout/familyForest.ts

@@ -82,7 +82,10 @@ export function buildFamilyForest(nodes: PersonNodeDTO[], edges: RelationshipDTO
 		} else if (e.relationType === 'SPOUSE_OF') {
 			addToSet(spouses, e.personId, e.relatedPersonId);
 			addToSet(spouses, e.relatedPersonId, e.personId);
-			spouseYear.set(pairKey(e.personId, e.relatedPersonId), e.fromYear ?? undefined);
+			spouseYear.set(
+				pairKey(e.personId, e.relatedPersonId),
+				e.fromDate ? Number(e.fromDate.slice(0, 4)) : undefined
+			);
 		}
 	}
 

frontend/src/lib/person/genealogy/layout/highlightLineage.test.ts

@@ -13,7 +13,9 @@ function parentEdge(parentId: string, childId: string, id = parentId + childId):
 		relatedPersonId: childId,
 		personDisplayName: '',
 		relatedPersonDisplayName: '',
-		relationType: 'PARENT_OF'
+		relationType: 'PARENT_OF',
+		fromDatePrecision: 'UNKNOWN',
+		toDatePrecision: 'UNKNOWN'
 	};
 }
 
@@ -24,7 +26,9 @@ function spouseEdge(a: string, b: string, id = a + b): RelationshipDTO {
 		relatedPersonId: b,
 		personDisplayName: '',
 		relatedPersonDisplayName: '',
-		relationType: 'SPOUSE_OF'
+		relationType: 'SPOUSE_OF',
+		fromDatePrecision: 'UNKNOWN',
+		toDatePrecision: 'UNKNOWN'
 	};
 }
 
@@ -35,7 +39,9 @@ function siblingEdge(a: string, b: string, id = a + b): RelationshipDTO {
 		relatedPersonId: b,
 		personDisplayName: '',
 		relatedPersonDisplayName: '',
-		relationType: 'SIBLING_OF'
+		relationType: 'SIBLING_OF',
+		fromDatePrecision: 'UNKNOWN',
+		toDatePrecision: 'UNKNOWN'
 	};
 }
 

frontend/src/lib/person/personLifeDates.ts

@@ -1,23 +1,17 @@
-import { formatDocumentDate, type DatePrecision } from '$lib/shared/utils/documentDate';
+import { formatDatePart, type DatePrecision } from '$lib/shared/utils/documentDate';
 
 /**
- * Formats one life date (birth or death) at the precision the data claims,
+ * Formats one life date (birth or death) at the precision the data claims.
- * delegating all rendering to {@link formatDocumentDate}. Returns '' for a
+ * Thin domain alias over the shared {@link formatDatePart}: carries no * / †
- * missing date. Carries no * / † glyph — components that need the glyphs wrap
+ * glyph — components that need the glyphs wrap them in their own `aria-hidden`
- * them in their own `aria-hidden` markup so screen readers only hear the date.
+ * markup so screen readers only hear the date.
- *
- * A missing precision falls back to YEAR: pre-V76 rows only knew a year, and
- * a bare year is the only safe rendering for a date without precision metadata.
  */
 export function formatLifeDate(
 	date: string | null | undefined,
 	precision: DatePrecision | null | undefined,
 	locale?: string
 ): string {
-	if (!date) {
+	return formatDatePart(date, precision, locale);
-		return '';
-	}
-	return formatDocumentDate(date, precision ?? 'YEAR', null, null, locale);
 }
 
 /**

frontend/src/lib/person/relationship/AddRelationshipForm.svelte

@@ -1,8 +1,11 @@
 <script lang="ts">
+import { onMount } from 'svelte';
 import { enhance } from '$app/forms';
 import { m } from '$lib/paraglide/messages.js';
 import PersonTypeahead from '$lib/person/PersonTypeahead.svelte';
+import RelationshipDateField from '$lib/person/relationship/RelationshipDateField.svelte';
 import type { components } from '$lib/generated/api';
+import type { DatePrecision } from '$lib/shared/utils/documentDate';
 
 type RelationshipDTO = components['schemas']['RelationshipDTO'];
 type RelationType = NonNullable<RelationshipDTO['relationType']>;
@@ -10,71 +13,96 @@ type RelationType = NonNullable<RelationshipDTO['relationType']>;
 export type RelFormData = {
 	relatedPersonId: string;
 	relationType: RelationType;
-	fromYear?: number;
+	fromDate?: string;
-	toYear?: number;
+	fromDatePrecision?: DatePrecision;
+	toDate?: string;
+	toDatePrecision?: DatePrecision;
+	notes?: string;
 };
 
 interface Props {
 	personId: string;
+	// When present the form is an EDIT: pre-filled and posting to ?/updateRelationship.
+	relationship?: RelationshipDTO;
 	onSubmit?: (data: RelFormData) => Promise<void>;
+	onClose?: () => void;
 }
 
-let { personId, onSubmit }: Props = $props();
+let { personId, relationship, onSubmit, onClose }: Props = $props();
+
+const isEdit = $derived(relationship != null);
 
 let open = $state(false);
 let addType = $state<RelationType>('PARENT_OF');
 let addRelatedPersonId = $state('');
 let addRelatedPersonName = $state('');
-let addFromYear = $state('');
+let notes = $state('');
-let addToYear = $state('');
 let callbackError = $state<string | null>(null);
+let submitting = $state(false);
 
-const yearError = $derived.by(() => {
+// Seed once at mount (reading props in a closure avoids state_referenced_locally).
-	const from = addFromYear.trim();
+// The parent re-creates this form per edited row, so the relationship never
-	const to = addToYear.trim();
+// changes under a live instance.
-	if (!from || !to) return null;
+onMount(() => {
-	const fromInt = parseInt(from, 10);
+	if (!relationship) return;
-	const toInt = parseInt(to, 10);
+	open = true;
-	if (Number.isNaN(fromInt) || Number.isNaN(toInt)) return null;
+	addType = relationship.relationType ?? 'PARENT_OF';
-	return toInt < fromInt ? m.relation_year_error_bis_before_von() : null;
+	const viewpointIsSubject = relationship.personId === personId;
+	addRelatedPersonId =
+		(viewpointIsSubject ? relationship.relatedPersonId : relationship.personId) ?? '';
+	addRelatedPersonName =
+		(viewpointIsSubject ? relationship.relatedPersonDisplayName : relationship.personDisplayName) ??
+		'';
+	notes = relationship.notes ?? '';
 });
 
 const selfError = $derived(
 	addRelatedPersonId !== '' && addRelatedPersonId === personId ? m.relation_error_self() : null
 );
 
-const submitDisabled = $derived(
+const submitDisabled = $derived(selfError !== null || addRelatedPersonId === '');
-	yearError !== null || selfError !== null || addRelatedPersonId === ''
-);
 
 function reset() {
 	addType = 'PARENT_OF';
 	addRelatedPersonId = '';
 	addRelatedPersonName = '';
-	addFromYear = '';
+	notes = '';
-	addToYear = '';
 	callbackError = null;
 }
 
 function cancel() {
+	if (isEdit) {
+		onClose?.();
+		return;
+	}
 	open = false;
 	reset();
 }
 
-async function handleCallbackSubmit(event: Event) {
+async function handleCallbackSubmit(event: SubmitEvent) {
 	event.preventDefault();
 	if (submitDisabled || !onSubmit) return;
-	const data: RelFormData = { relatedPersonId: addRelatedPersonId, relationType: addType };
+	const fd = new FormData(event.currentTarget as HTMLFormElement);
-	const from = parseInt(addFromYear.trim(), 10);
+	const fromDate = (fd.get('fromDate') as string) || undefined;
-	if (!Number.isNaN(from)) data.fromYear = from;
+	const toDate = (fd.get('toDate') as string) || undefined;
-	const to = parseInt(addToYear.trim(), 10);
+	const data: RelFormData = {
-	if (!Number.isNaN(to)) data.toYear = to;
+		relatedPersonId: addRelatedPersonId,
+		relationType: addType,
+		fromDate,
+		fromDatePrecision: fromDate ? (fd.get('fromDatePrecision') as DatePrecision) : undefined,
+		toDate,
+		toDatePrecision: toDate ? (fd.get('toDatePrecision') as DatePrecision) : undefined,
+		notes: (fd.get('notes') as string)?.trim() || undefined
+	};
+	submitting = true;
 	try {
 		await onSubmit(data);
 		open = false;
 		reset();
 	} catch {
 		callbackError = m.error_internal_error();
+	} finally {
+		submitting = false;
 	}
 }
 </script>
@@ -113,39 +141,32 @@ async function handleCallbackSubmit(event: Event) {
 				compact
 			/>
 		</div>
-		<label class="block">
-			<span class="font-sans text-xs font-medium text-ink-2"
-				>{m.relation_form_field_from_year()}</span
-			>
-			<input
-				type="text"
-				name="fromYear"
-				inputmode="numeric"
-				pattern="[0-9]*"
-				bind:value={addFromYear}
-				placeholder={m.relation_form_year_placeholder()}
-				class="mt-1 block w-full rounded-sm border border-line bg-surface px-2 py-1.5 text-sm text-ink focus:border-primary focus:outline-none"
-			/>
-		</label>
-		<label class="block">
-			<span class="font-sans text-xs font-medium text-ink-2">{m.relation_form_field_to_year()}</span
-			>
-			<input
-				type="text"
-				name="toYear"
-				inputmode="numeric"
-				pattern="[0-9]*"
-				bind:value={addToYear}
-				aria-describedby={yearError ? 'add-rel-year-error' : undefined}
-				class="mt-1 block w-full rounded-sm border border-line bg-surface px-2 py-1.5 text-sm text-ink focus:border-primary focus:outline-none"
-			/>
-			{#if yearError}
-				<p id="add-rel-year-error" class="mt-1 text-xs text-red-700" role="alert">
-					{yearError}
-				</p>
-			{/if}
-		</label>
 	</div>
+	<div class="mt-3 grid gap-3 md:grid-cols-2">
+		<RelationshipDateField
+			name="fromDate"
+			legend={m.relation_label_from_date()}
+			initialIso={relationship?.fromDate ?? ''}
+			initialPrecision={relationship?.fromDatePrecision ?? null}
+		/>
+		<RelationshipDateField
+			name="toDate"
+			legend={m.relation_label_to_date()}
+			initialIso={relationship?.toDate ?? ''}
+			initialPrecision={relationship?.toDatePrecision ?? null}
+		/>
+	</div>
+	<label class="mt-3 block">
+		<span class="font-sans text-xs font-medium text-ink-2">{m.relation_label_notes()}</span>
+		<textarea
+			name="notes"
+			maxlength="2000"
+			rows="2"
+			bind:value={notes}
+			placeholder={m.relation_notes_placeholder()}
+			class="mt-1 block w-full rounded-sm border border-line bg-surface px-2 py-1.5 font-serif text-sm text-ink-3 focus:border-primary focus:outline-none"
+		></textarea>
+	</label>
 	{#if selfError}
 		<p class="mt-2 text-xs text-red-700" role="alert">{selfError}</p>
 	{/if}
@@ -162,10 +183,18 @@ async function handleCallbackSubmit(event: Event) {
 		</button>
 		<button
 			type="submit"
-			disabled={submitDisabled}
+			disabled={submitDisabled || submitting}
-			class="rounded-sm bg-primary px-3 py-1.5 font-sans text-xs font-medium text-primary-fg transition hover:bg-primary/80 disabled:opacity-40"
+			aria-busy={submitting}
+			class="inline-flex items-center gap-1.5 rounded-sm bg-primary px-3 py-1.5 font-sans text-xs font-medium text-primary-fg transition hover:bg-primary/80 disabled:opacity-40"
 		>
-			{m.relation_btn_add()}
+			{#if submitting}
+				<span
+					class="h-3 w-3 animate-spin rounded-full border-2 border-primary-fg/40 border-t-primary-fg"
+					data-testid="submit-spinner"
+					aria-hidden="true"
+				></span>
+			{/if}
+			{isEdit ? m.relation_btn_save() : m.relation_btn_add()}
 		</button>
 	</div>
 {/snippet}
@@ -185,18 +214,27 @@ async function handleCallbackSubmit(event: Event) {
 {:else}
 	<form
 		method="POST"
-		action="?/addRelationship"
+		action={isEdit ? '?/updateRelationship' : '?/addRelationship'}
 		use:enhance={() => {
+			submitting = true;
 			return async ({ result, update }) => {
 				await update();
+				submitting = false;
 				if (result.type === 'success') {
+					if (isEdit) {
+						onClose?.();
+					} else {
 						open = false;
 						reset();
 					}
+				}
 			};
 		}}
 		class="mt-3 rounded-sm border border-line bg-muted/40 p-3"
 	>
+		{#if relationship}
+			<input type="hidden" name="relId" value={relationship.id} />
+		{/if}
 		{@render formFields()}
 	</form>
 {/if}

frontend/src/lib/person/relationship/AddRelationshipForm.svelte.spec.ts

@@ -8,58 +8,116 @@ vi.mock('$lib/person/PersonTypeahead.svelte', () => ({ default: () => null }));
 
 afterEach(cleanup);
 
-describe('AddRelationshipForm', () => {
+const PID = 'person-1';
-	it('shows add-relationship button initially and no form', async () => {
+const OTHER = 'person-2';
-		render(AddRelationshipForm, { personId: 'person-1' });
+
+const editRel = () => ({
+	id: 'rel-9',
+	personId: PID,
+	relatedPersonId: OTHER,
+	personDisplayName: 'Anna Müller',
+	relatedPersonDisplayName: 'Hans Müller',
+	relationType: 'SPOUSE_OF' as const,
+	fromDate: '1923-05-12',
+	fromDatePrecision: 'DAY' as const,
+	toDatePrecision: 'UNKNOWN' as const,
+	notes: 'Hochzeit in Berlin'
+});
+
+describe('AddRelationshipForm — create mode', () => {
+	it('shows the add-relationship toggle initially and no form', async () => {
+		render(AddRelationshipForm, { personId: PID });
 		await expect.element(page.getByRole('button')).toBeInTheDocument();
-		await expect.element(page.getByRole('combobox')).not.toBeInTheDocument();
+		expect(document.querySelector('select[name="relationType"]')).toBeNull();
 	});
 
-	it('shows relationType select when add button is clicked', async () => {
+	it('shows the relationType select when the add toggle is clicked', async () => {
-		render(AddRelationshipForm, { personId: 'person-1' });
+		render(AddRelationshipForm, { personId: PID });
 		document.querySelector<HTMLButtonElement>('button')!.click();
-		await expect.element(page.getByRole('combobox')).toBeInTheDocument();
+		await expect.element(page.getByRole('combobox', { name: 'Typ' })).toBeInTheDocument();
 	});
 
-	it('hides form and shows button when cancel is clicked', async () => {
+	it('hides the form and shows the toggle again on cancel', async () => {
-		render(AddRelationshipForm, { personId: 'person-1' });
+		render(AddRelationshipForm, { personId: PID });
 		document.querySelector<HTMLButtonElement>('button')!.click();
-		await expect.element(page.getByRole('combobox')).toBeInTheDocument();
+		await expect.element(page.getByRole('combobox', { name: 'Typ' })).toBeInTheDocument();
 		const cancelBtn = [...document.querySelectorAll<HTMLButtonElement>('button')].find(
 			(b) => b.type === 'button' && /abbrechen/i.test(b.textContent ?? '')
 		);
 		cancelBtn!.click();
-		await expect.element(page.getByRole('combobox')).not.toBeInTheDocument();
+		await vi.waitFor(() =>
+			expect(document.querySelector('select[name="relationType"]')).toBeNull()
+		);
 	});
 
-	it('submit is disabled when no person is selected', async () => {
+	it('disables submit when no person is selected', async () => {
-		render(AddRelationshipForm, { personId: 'person-1' });
+		render(AddRelationshipForm, { personId: PID });
 		document.querySelector<HTMLButtonElement>('button')!.click();
 		await expect.element(page.getByRole('button', { name: /^Hinzufügen$/i })).toBeDisabled();
 	});
 
-	it('form has no server action when onSubmit prop is provided', async () => {
+	it('has no server action when an onSubmit prop is provided', async () => {
 		const onSubmit = vi.fn().mockResolvedValue(undefined);
-		render(AddRelationshipForm, { personId: 'person-1', onSubmit });
+		render(AddRelationshipForm, { personId: PID, onSubmit });
 		document.querySelector<HTMLButtonElement>('button')!.click();
-		await expect.element(page.getByRole('combobox')).toBeInTheDocument();
+		await expect.element(page.getByRole('combobox', { name: 'Typ' })).toBeInTheDocument();
-		const form = document.querySelector('form');
+		expect(document.querySelector('form')?.hasAttribute('action')).toBe(false);
-		expect(form?.hasAttribute('action')).toBe(false);
+	});
-	});
+});
-
+
-	it('shows year-range error when toYear is before fromYear', async () => {
+describe('AddRelationshipForm — edit mode', () => {
-		render(AddRelationshipForm, { personId: 'person-1' });
+	it('opens pre-filled and labels the submit "Speichern"', async () => {
-		document.querySelector<HTMLButtonElement>('button')!.click();
+		render(AddRelationshipForm, { personId: PID, relationship: editRel() });
-		await expect.element(page.getByRole('combobox')).toBeInTheDocument();
+		await expect.element(page.getByRole('button', { name: /^Speichern$/i })).toBeInTheDocument();
-
+	});
-		const fromInput = document.querySelector<HTMLInputElement>('input[name="fromYear"]')!;
+
-		fromInput.value = '1935';
+	it('pre-fills the from-date as dd.mm.yyyy', async () => {
-		fromInput.dispatchEvent(new InputEvent('input', { bubbles: true }));
+		render(AddRelationshipForm, { personId: PID, relationship: editRel() });
-
+		await expect.element(page.getByRole('combobox', { name: 'Typ' })).toBeInTheDocument();
-		const toInput = document.querySelector<HTMLInputElement>('input[name="toYear"]')!;
+		const fromInput = document.querySelector<HTMLInputElement>('#fromDate')!;
-		toInput.value = '1920';
+		await vi.waitFor(() => expect(fromInput.value).toBe('12.05.1923'));
-		toInput.dispatchEvent(new InputEvent('input', { bubbles: true }));
+	});
-
+
-		await expect.element(page.getByRole('alert')).toBeVisible();
+	it('round-trips the notes into the textarea', async () => {
+		render(AddRelationshipForm, { personId: PID, relationship: editRel() });
+		await expect.element(page.getByRole('combobox', { name: 'Typ' })).toBeInTheDocument();
+		const notes = document.querySelector<HTMLTextAreaElement>('textarea[name="notes"]')!;
+		await vi.waitFor(() => expect(notes.value).toBe('Hochzeit in Berlin'));
+	});
+
+	it('offers only DAY/MONTH/YEAR in each precision select', async () => {
+		render(AddRelationshipForm, { personId: PID, relationship: editRel() });
+		await expect.element(page.getByRole('combobox', { name: 'Typ' })).toBeInTheDocument();
+		const options = [
+			...document.querySelectorAll<HTMLOptionElement>('#fromDatePrecision option')
+		].map((o) => o.value);
+		expect(options).toEqual(['DAY', 'MONTH', 'YEAR']);
+	});
+
+	it('gives each date input an associated label (accessible name)', async () => {
+		render(AddRelationshipForm, { personId: PID, relationship: editRel() });
+		await expect.element(page.getByRole('combobox', { name: 'Typ' })).toBeInTheDocument();
+		expect(document.querySelector('#fromDate')?.getAttribute('aria-label')).toBe('Beginn (Datum)');
+		expect(document.querySelector('#toDate')?.getAttribute('aria-label')).toBe('Ende (Datum)');
+	});
+
+	it('disables the submit and shows a progress spinner while a submit is in flight', async () => {
+		let resolve: () => void = () => {};
+		const onSubmit = vi.fn(() => new Promise<void>((r) => (resolve = r)));
+		render(AddRelationshipForm, { personId: PID, relationship: editRel(), onSubmit });
+
+		const submit = await vi.waitFor(() => {
+			const b = [...document.querySelectorAll<HTMLButtonElement>('button')].find(
+				(x) => x.type === 'submit'
+			);
+			if (!b) throw new Error('submit not ready');
+			return b;
+		});
+		submit.click();
+
+		await expect.element(page.getByTestId('submit-spinner')).toBeInTheDocument();
+		await vi.waitFor(() => expect(submit.disabled).toBe(true));
+		expect(onSubmit).toHaveBeenCalledOnce();
+		resolve();
 	});
 });

frontend/src/lib/person/relationship/AddRelationshipForm.svelte.test.ts

@@ -33,36 +33,6 @@ describe('AddRelationshipForm', () => {
 		expect(optionValues).toContain('OTHER');
 	});
 
-	it('shows the year-error alert when toYear is before fromYear', async () => {
-		render(AddRelationshipForm, { props: { personId: 'p-1' } });
-
-		await page.getByRole('button', { name: /hinzufügen/i }).click();
-
-		const fromInput = document.querySelector('input[name="fromYear"]') as HTMLInputElement;
-		const toInput = document.querySelector('input[name="toYear"]') as HTMLInputElement;
-		fromInput.value = '1923';
-		fromInput.dispatchEvent(new Event('input', { bubbles: true }));
-		toInput.value = '1920';
-		toInput.dispatchEvent(new Event('input', { bubbles: true }));
-
-		await expect.element(page.getByText(/bis-jahr darf nicht vor von-jahr/i)).toBeVisible();
-	});
-
-	it('does not show the year-error when toYear equals fromYear', async () => {
-		render(AddRelationshipForm, { props: { personId: 'p-1' } });
-
-		await page.getByRole('button', { name: /hinzufügen/i }).click();
-
-		const fromInput = document.querySelector('input[name="fromYear"]') as HTMLInputElement;
-		const toInput = document.querySelector('input[name="toYear"]') as HTMLInputElement;
-		fromInput.value = '1923';
-		fromInput.dispatchEvent(new Event('input', { bubbles: true }));
-		toInput.value = '1923';
-		toInput.dispatchEvent(new Event('input', { bubbles: true }));
-
-		await expect.element(page.getByText(/bis-jahr darf nicht/i)).not.toBeInTheDocument();
-	});
-
 	it('cancel button closes the form', async () => {
 		render(AddRelationshipForm, { props: { personId: 'p-1' } });
 
@@ -136,25 +106,4 @@ describe('AddRelationshipForm', () => {
 			expect(submitBtn!.disabled).toBe(true);
 		});
 	});
-
-	it('keeps submit disabled when there is a yearError', async () => {
-		render(AddRelationshipForm, { props: { personId: 'p-1' } });
-
-		await page.getByRole('button', { name: /hinzufügen/i }).click();
-
-		const fromInput = document.querySelector('input[name="fromYear"]') as HTMLInputElement;
-		const toInput = document.querySelector('input[name="toYear"]') as HTMLInputElement;
-		const relInput = document.querySelector('input[name="relatedPersonId"]') as HTMLInputElement;
-		fromInput.value = '1923';
-		fromInput.dispatchEvent(new Event('input', { bubbles: true }));
-		toInput.value = '1920';
-		toInput.dispatchEvent(new Event('input', { bubbles: true }));
-		relInput.value = 'p-other';
-		relInput.dispatchEvent(new Event('input', { bubbles: true }));
-
-		await vi.waitFor(() => {
-			const submitBtn = document.querySelector('button[type="submit"]') as HTMLButtonElement;
-			expect(submitBtn.disabled).toBe(true);
-		});
-	});
 });

frontend/src/lib/person/relationship/RelationshipChip.svelte

@@ -5,12 +5,13 @@ import { m } from '$lib/paraglide/messages.js';
 interface Props {
 	chipLabel: string;
 	otherName: string;
-	yearRange?: string;
+	dateRange?: string;
 	canWrite: boolean;
 	relId: string;
+	onEdit?: () => void;
 }
 
-let { chipLabel, otherName, yearRange = '', canWrite, relId }: Props = $props();
+let { chipLabel, otherName, dateRange = '', canWrite, relId, onEdit }: Props = $props();
 </script>
 
 <li class="flex items-center gap-2 py-2">
@@ -22,8 +23,31 @@ let { chipLabel, otherName, yearRange = '', canWrite, relId }: Props = $props();
 	<span class="min-w-0 flex-1 truncate font-serif text-sm text-ink">
 		{otherName}
 	</span>
-	{#if yearRange}
+	{#if dateRange}
-		<span class="shrink-0 font-sans text-xs text-ink-3" data-testid="year-range">{yearRange}</span>
+		<span class="shrink-0 font-sans text-xs text-ink-3" data-testid="date-range">{dateRange}</span>
+	{/if}
+	{#if canWrite && onEdit}
+		<button
+			type="button"
+			onclick={onEdit}
+			aria-label="{m.relation_edit()} — {otherName}"
+			class="inline-flex h-11 w-11 items-center justify-center text-ink-3 transition-colors hover:text-primary"
+		>
+			<svg
+				class="h-3.5 w-3.5"
+				viewBox="0 0 24 24"
+				fill="none"
+				stroke="currentColor"
+				stroke-width="2"
+				aria-hidden="true"
+			>
+				<path
+					stroke-linecap="round"
+					stroke-linejoin="round"
+					d="M16.862 4.487l1.687-1.688a1.875 1.875 0 112.652 2.652L10.582 16.07a4.5 4.5 0 01-1.897 1.13L6 18l.8-2.685a4.5 4.5 0 011.13-1.897l8.932-8.931z"
+				/>
+			</svg>
+		</button>
 	{/if}
 	{#if canWrite}
 		<form method="POST" action="?/deleteRelationship" use:enhance class="shrink-0">

frontend/src/lib/person/relationship/RelationshipChip.svelte.spec.ts

@@ -10,7 +10,7 @@ afterEach(cleanup);
 const baseProps = {
 	chipLabel: 'Elternteil',
 	otherName: 'Anna Schmidt',
-	yearRange: '',
+	dateRange: '',
 	canWrite: false,
 	relId: 'rel-1'
 };
@@ -26,30 +26,55 @@ describe('RelationshipChip', () => {
 		await expect.element(page.getByText('Anna Schmidt')).toBeInTheDocument();
 	});
 
-	it('shows year range when provided', async () => {
+	it('shows the date range when provided', async () => {
-		render(RelationshipChip, { ...baseProps, yearRange: '1920–1980' });
+		render(RelationshipChip, { ...baseProps, dateRange: '12. Mai 1923 – 1958' });
-		await expect.element(page.getByText('1920–1980')).toBeInTheDocument();
+		await expect.element(page.getByText('12. Mai 1923 – 1958')).toBeInTheDocument();
 	});
 
-	it('does not show year range span when empty', async () => {
+	it('does not render a date-range span when empty', async () => {
-		render(RelationshipChip, { ...baseProps, yearRange: '' });
+		render(RelationshipChip, { ...baseProps, dateRange: '' });
-		expect(document.querySelector('[data-testid="year-range"]')).toBeNull();
+		expect(document.querySelector('[data-testid="date-range"]')).toBeNull();
 	});
 
-	it('shows delete button when canWrite is true', async () => {
+	it('shows the delete button when canWrite is true', async () => {
 		render(RelationshipChip, { ...baseProps, canWrite: true });
 		await expect.element(page.getByRole('button')).toBeInTheDocument();
 	});
 
-	it('hides delete button when canWrite is false', async () => {
+	it('hides the delete button when canWrite is false', async () => {
 		render(RelationshipChip, { ...baseProps, canWrite: false });
 		expect(document.querySelector('button')).toBeNull();
 	});
 
-	it('delete button has h-11 w-11 (44px) WCAG touch target class', async () => {
+	it('gives the delete button an h-11 w-11 (44px) WCAG touch target', async () => {
 		render(RelationshipChip, { ...baseProps, canWrite: true });
 		const btn = document.querySelector('button')!;
 		expect(btn.className).toContain('h-11');
 		expect(btn.className).toContain('w-11');
 	});
+
+	it('shows an Edit affordance with an accessible name when canWrite and onEdit', async () => {
+		render(RelationshipChip, { ...baseProps, canWrite: true, onEdit: () => {} });
+		await expect
+			.element(page.getByRole('button', { name: /Beziehung bearbeiten/i }))
+			.toBeInTheDocument();
+	});
+
+	it('does not show the Edit affordance without onEdit', async () => {
+		render(RelationshipChip, { ...baseProps, canWrite: true });
+		expect(document.querySelector('button[aria-label*="bearbeiten"]')).toBeNull();
+	});
+
+	it('does not show the Edit affordance when canWrite is false', async () => {
+		render(RelationshipChip, { ...baseProps, canWrite: false, onEdit: () => {} });
+		expect(document.querySelector('button[aria-label*="bearbeiten"]')).toBeNull();
+	});
+
+	it('calls onEdit when the Edit affordance is clicked', async () => {
+		const onEdit = vi.fn();
+		render(RelationshipChip, { ...baseProps, canWrite: true, onEdit });
+		const editBtn = document.querySelector<HTMLButtonElement>('button[aria-label*="bearbeiten"]')!;
+		editBtn.click();
+		expect(onEdit).toHaveBeenCalledOnce();
+	});
 });

frontend/src/lib/person/relationship/RelationshipDateField.svelte

@@ -0,0 +1,38 @@
+<script lang="ts">
+import { m } from '$lib/paraglide/messages.js';
+import DateInputWithPrecision from '$lib/shared/primitives/DateInputWithPrecision.svelte';
+import type { DatePrecision } from '$lib/shared/utils/documentDate';
+
+// Only DAY / MONTH / YEAR are offered (same as the person life-date field and the
+// 60+ author audience). Storage still accepts all seven precisions; SEASON/RANGE/
+// APPROX render correctly elsewhere but make no sense to enter for a relationship.
+let {
+	name,
+	legend,
+	initialIso = '',
+	initialPrecision = null
+}: {
+	name: string;
+	legend: string;
+	initialIso?: string | null;
+	initialPrecision?: string | null;
+} = $props();
+
+const precisions: { value: DatePrecision; label: string }[] = $derived([
+	{ value: 'DAY', label: m.relation_precision_day() },
+	{ value: 'MONTH', label: m.relation_precision_month() },
+	{ value: 'YEAR', label: m.relation_precision_year() }
+]);
+</script>
+
+<DateInputWithPrecision
+	name={name}
+	legend={legend}
+	precisionLabel={m.relation_label_date_precision()}
+	precisions={precisions}
+	hint={m.relation_date_placeholder_hint()}
+	initialIso={initialIso}
+	initialPrecision={initialPrecision}
+	inputClass="bg-surface"
+	selectClass="bg-surface text-ink-3"
+/>

frontend/src/lib/person/relationshipDates.spec.ts

@@ -0,0 +1,65 @@
+import { describe, expect, it } from 'vitest';
+import { formatRelationshipDateRange } from './relationshipDates';
+
+// Delegates all precision rendering to formatDocumentDate — these tests pin the
+// composition (dash, single sides, empty state) and one rendering per precision,
+// plus en/es for DAY/MONTH so a German-month leak is caught here, not on a card.
+describe('formatRelationshipDateRange', () => {
+	describe('both dates (de default)', () => {
+		it('renders DAY precision as full dates', () => {
+			expect(formatRelationshipDateRange('1923-05-12', 'DAY', '1958-06-13', 'DAY')).toBe(
+				'12. Mai 1923 – 13. Juni 1958'
+			);
+		});
+
+		it('renders MONTH precision as month + year', () => {
+			expect(formatRelationshipDateRange('1923-05-01', 'MONTH', '1958-06-01', 'MONTH')).toBe(
+				'Mai 1923 – Juni 1958'
+			);
+		});
+
+		it('renders YEAR precision as bare years', () => {
+			expect(formatRelationshipDateRange('1923-01-01', 'YEAR', '1958-01-01', 'YEAR')).toBe(
+				'1923 – 1958'
+			);
+		});
+
+		it('renders mixed precisions per side', () => {
+			expect(formatRelationshipDateRange('1923-05-12', 'DAY', '1958-01-01', 'YEAR')).toBe(
+				'12. Mai 1923 – 1958'
+			);
+		});
+	});
+
+	describe('single sides and empty states', () => {
+		it('renders from only without a trailing dash', () => {
+			expect(formatRelationshipDateRange('1923-05-12', 'DAY', null, null)).toBe('12. Mai 1923');
+		});
+
+		it('renders to only with a leading dash', () => {
+			expect(formatRelationshipDateRange(null, null, '1958-06-13', 'DAY')).toBe('– 13. Juni 1958');
+		});
+
+		it('renders nothing when both dates are missing (UNKNOWN)', () => {
+			expect(formatRelationshipDateRange(null, 'UNKNOWN', null, 'UNKNOWN')).toBe('');
+		});
+
+		it('renders nothing for a from-only with a null date', () => {
+			expect(formatRelationshipDateRange(null, null, null, null)).toBe('');
+		});
+	});
+
+	describe('localized months (catch German-month leak)', () => {
+		it('renders DAY in English with no German month name', () => {
+			const out = formatRelationshipDateRange('1923-05-12', 'DAY', null, null, 'en');
+			expect(out).toContain('May');
+			expect(out).not.toContain('Mai');
+			expect(out).toContain('1923');
+		});
+
+		it('renders MONTH in Spanish', () => {
+			const out = formatRelationshipDateRange('1923-05-01', 'MONTH', null, null, 'es');
+			expect(out.toLowerCase()).toContain('mayo');
+		});
+	});
+});

frontend/src/lib/person/relationshipDates.ts

@@ -0,0 +1,30 @@
+import { formatDatePart, type DatePrecision } from '$lib/shared/utils/documentDate';
+
+/**
+ * Formats a relationship's start–end range as plain text, e.g. for a marriage row.
+ * Examples (de):
+ *   12. Mai 1923 – 13. Juni 1958   (both)
+ *   12. Mai 1923                   (start only — no trailing dash)
+ *   – 13. Juni 1958                (end only)
+ *   ""                             (neither — the caller renders no date line)
+ */
+export function formatRelationshipDateRange(
+	fromDate: string | null | undefined,
+	fromDatePrecision: DatePrecision | null | undefined,
+	toDate: string | null | undefined,
+	toDatePrecision: DatePrecision | null | undefined,
+	locale?: string
+): string {
+	const from = formatDatePart(fromDate, fromDatePrecision, locale);
+	const to = formatDatePart(toDate, toDatePrecision, locale);
+	if (from && to) {
+		return `${from} – ${to}`;
+	}
+	if (from) {
+		return from;
+	}
+	if (to) {
+		return `– ${to}`;
+	}
+	return '';
+}

frontend/src/lib/person/relationshipLabels.test.ts

@@ -19,6 +19,8 @@ function makeRel(
 		personDisplayName: 'Alice',
 		relatedPersonDisplayName: 'Bob',
 		relationType,
+		fromDatePrecision: 'UNKNOWN',
+		toDatePrecision: 'UNKNOWN',
 		...override
 	};
 }

frontend/src/lib/shared/errors.ts

@@ -10,6 +10,7 @@ export type ErrorCode =
 	| 'INVALID_PERSON_TYPE'
 	| 'BIRTH_AFTER_DEATH'
 	| 'INVALID_DATE_PRECISION'
+	| 'INVALID_RELATIONSHIP_DATES'
 	| 'INVALID_DATE_RANGE'
 	| 'DOCUMENT_NOT_FOUND'
 	| 'DOCUMENT_NO_FILE'
@@ -106,6 +107,8 @@ export function getErrorMessage(code: ErrorCode | string | undefined): string {
 			return m.error_birth_after_death();
 		case 'INVALID_DATE_PRECISION':
 			return m.error_invalid_date_precision();
+		case 'INVALID_RELATIONSHIP_DATES':
+			return m.error_invalid_relationship_dates();
 		case 'INVALID_DATE_RANGE':
 			return m.error_invalid_date_range();
 		case 'DOCUMENT_NOT_FOUND':

frontend/src/lib/shared/primitives/DateInputWithPrecision.svelte

@@ -0,0 +1,106 @@
+<script lang="ts">
+import { onMount } from 'svelte';
+import DateInput from '$lib/shared/primitives/DateInput.svelte';
+import type { DatePrecision } from '$lib/shared/utils/documentDate';
+
+/**
+ * Compact date + precision field: the {@link DateInput} primitive paired with a
+ * precision <select> offering a caller-chosen subset of precisions. Shared base of
+ * PersonLifeDateField (birth/death) and RelationshipDateField (from/to).
+ *
+ * Distinct from {@link DatePrecisionField} — that one is the full document/timeline
+ * field (all seven precisions, German free-text entry, RANGE end-date disclosure).
+ * This one is the restricted, single-input variant for the person-family forms.
+ *
+ * All copy (legend, precision labels, hint, the select's accessible name) and the
+ * offered precisions are injected by the caller so this stays domain-agnostic.
+ */
+let {
+	name,
+	legend,
+	precisionLabel,
+	hint,
+	precisions,
+	initialIso = '',
+	initialPrecision = null,
+	inputClass = '',
+	selectClass = ''
+}: {
+	name: string;
+	legend: string;
+	precisionLabel: string;
+	hint: string;
+	precisions: { value: DatePrecision; label: string }[];
+	initialIso?: string | null;
+	initialPrecision?: string | null;
+	inputClass?: string;
+	selectClass?: string;
+} = $props();
+
+let iso = $state('');
+let errorMessage = $state<string | null>(null);
+let inputEl = $state<HTMLInputElement | undefined>();
+let precision = $state<DatePrecision>('DAY');
+
+// Seed once at mount so a later load() rerun does not stomp an in-progress edit.
+onMount(() => {
+	if (initialIso) {
+		iso = initialIso;
+	}
+	const offered = precisions.some((p) => p.value === initialPrecision);
+	if (offered) {
+		precision = initialPrecision as DatePrecision;
+	} else if (initialIso) {
+		// A stored non-offered precision (SEASON/RANGE/APPROX) seeds as YEAR so an
+		// untouched save does not silently claim DAY precision for the stored date.
+		precision = 'YEAR';
+	}
+});
+
+// A partial date leaves the hidden ISO empty — block native submission until the
+// date is completed or fully emptied, so a save can never silently clear a date.
+$effect(() => {
+	inputEl?.setCustomValidity(errorMessage ?? '');
+});
+
+const controlCls =
+	'block min-h-[44px] w-full rounded border border-line px-3 py-2 font-serif text-ink focus:outline-none focus-visible:ring-2 focus-visible:ring-focus-ring';
+</script>
+
+<fieldset>
+	<legend class="mb-1 block text-xs font-bold tracking-widest text-ink-3 uppercase">
+		{legend}
+	</legend>
+	<div class="flex flex-col gap-2 sm:flex-row">
+		<div class="flex-1">
+			<DateInput
+				bind:value={iso}
+				bind:errorMessage={errorMessage}
+				bind:inputEl={inputEl}
+				name={name}
+				id={name}
+				placeholder="TT.MM.JJJJ"
+				ariaLabel={legend}
+				ariaDescribedby={errorMessage ? `${name}-error` : undefined}
+				class="{controlCls} {inputClass}"
+			/>
+			{#if errorMessage}
+				<p id="{name}-error" class="mt-1 font-sans text-xs text-red-600">{errorMessage}</p>
+			{/if}
+		</div>
+		<div class="flex-1">
+			<select
+				id="{name}Precision"
+				name="{name}Precision"
+				aria-label="{legend}: {precisionLabel}"
+				bind:value={precision}
+				class="{controlCls} {selectClass}"
+			>
+				{#each precisions as p (p.value)}
+					<option value={p.value}>{p.label}</option>
+				{/each}
+			</select>
+		</div>
+	</div>
+	<p class="mt-1 font-sans text-xs text-ink-3">{hint}</p>
+</fieldset>

frontend/src/lib/shared/utils/documentDate.ts

@@ -66,6 +66,27 @@ export function formatDocumentDate(
 	}
 }
 
+/**
+ * Formats one nullable date at the precision the data claims, delegating all
+ * rendering to {@link formatDocumentDate}. Returns '' for a missing date; a
+ * missing precision falls back to YEAR — pre-precision rows knew only a year,
+ * and a bare year is the only safe rendering without precision metadata.
+ *
+ * This is the shared core of {@link formatLifeDate} (person birth/death) and the
+ * relationship from/to formatter. Range-level glyphs and dashes belong in those
+ * domain wrappers, never here.
+ */
+export function formatDatePart(
+	date: string | null | undefined,
+	precision: DatePrecision | null | undefined,
+	locale?: string
+): string {
+	if (!date) {
+		return '';
+	}
+	return formatDocumentDate(date, precision ?? 'YEAR', null, null, locale);
+}
+
 // ─── precision branches ──────────────────────────────────────────────────────
 
 function longDate(iso: string, locale: string): string {

frontend/src/lib/timeline/BucketHeaderChip.svelte

@@ -0,0 +1,64 @@
+<script lang="ts">
+import * as m from '$lib/paraglide/messages.js';
+
+/**
+ * The header chip of a Thema-mode root-tag bucket (#827, REQ-015): a *fully-tinted* chip whose
+ * fill and label both derive from the root tag's `--c-tag-*` colour token — distinct from the
+ * neutral per-letter {@link TagChip} (a surface pill with a tiny colour square). The label uses
+ * the saturated token as text over a subtle `color-mix` wash of the same token, so the ≥4.5:1
+ * label contrast holds in both light and dark themes. A `null` colour — or any value outside the
+ * known token set (the §2 `krieg`/`weih`/`fam` are demo class names, not tokens) — falls back to a
+ * neutral chip with no `var(--c-tag-)` reference, never a broken colour. The name is
+ * curator/import-derived and rendered through default `{...}` escaping, never the raw-HTML
+ * directive (REQ-009).
+ */
+const TAG_COLORS = new Set([
+	'sage',
+	'sienna',
+	'amber',
+	'slate',
+	'violet',
+	'rose',
+	'cobalt',
+	'moss',
+	'sand',
+	'coral'
+]);
+
+let { name, color }: { name: string; color: string | null } = $props();
+
+const token = $derived(color && TAG_COLORS.has(color) ? color : null);
+// The tint paints the chip's fill + dot only — never the label text. The saturated
+// --c-tag-* tokens used AS text over their own wash drop below WCAG AA 4.5:1 for the
+// light tokens (amber ≈3.0, sand ≈3.2, sage ≈3.4); a fixed dark ink keeps every token
+// legible while the 18% wash still reads as a genuinely tinted chip (REQ-015).
+const chipStyle = $derived(
+	token ? `background-color: color-mix(in srgb, var(--c-tag-${token}) 18%, transparent)` : ''
+);
+const dotStyle = $derived(token ? `background-color: var(--c-tag-${token})` : '');
+</script>
+
+<span
+	data-testid="bucket-header-chip"
+	title={name}
+	style={chipStyle}
+	class="inline-flex max-w-full items-center gap-1.5 rounded-full px-2.5 py-0.5 font-sans text-xs font-semibold"
+	class:border={!token}
+	class:border-line={!token}
+	class:bg-surface={!token}
+>
+	<span class="sr-only">{m.timeline_tag_chip_label()}: </span>
+	<span
+		data-testid="bucket-header-chip-dot"
+		aria-hidden="true"
+		style={dotStyle}
+		class="inline-block h-2 w-2 flex-shrink-0 rounded-sm"
+		class:bg-ink-3={!token}
+	></span>
+	<span
+		data-testid="bucket-header-chip-label"
+		style="overflow: hidden; text-overflow: ellipsis; white-space: nowrap; min-width: 0"
+		class:text-ink={token}
+		class:text-ink-3={!token}>{name}</span
+	>
+</span>

frontend/src/lib/timeline/BucketHeaderChip.svelte.spec.ts

@@ -0,0 +1,57 @@
+import { describe, it, expect, afterEach } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import * as m from '$lib/paraglide/messages.js';
+import BucketHeaderChip from './BucketHeaderChip.svelte';
+
+afterEach(() => cleanup());
+
+describe('BucketHeaderChip (REQ-015/009)', () => {
+	it('renders the root-tag name', () => {
+		render(BucketHeaderChip, { name: 'Krieg', color: 'sienna' });
+		expect(document.body.textContent).toContain('Krieg');
+	});
+
+	it('tints the chip with var(--c-tag-{token}) for a known colour token (REQ-015)', () => {
+		render(BucketHeaderChip, { name: 'Krieg', color: 'sienna' });
+		const chip = document.querySelector('[data-testid="bucket-header-chip"]') as HTMLElement;
+		expect(chip.getAttribute('style')).toContain('var(--c-tag-sienna)');
+	});
+
+	it('renders a neutral chip with no --c-tag- binding when colour is null (REQ-015)', () => {
+		render(BucketHeaderChip, { name: 'Ohne Thema', color: null });
+		expect(document.body.textContent).toContain('Ohne Thema');
+		expect(document.body.innerHTML).not.toContain('var(--c-tag-');
+	});
+
+	it('falls back to neutral for an unknown colour token, never a broken var (REQ-015)', () => {
+		// "krieg" is a §2 demo class name, not a real --c-tag-* token.
+		render(BucketHeaderChip, { name: 'Krieg', color: 'krieg' });
+		expect(document.body.innerHTML).not.toContain('var(--c-tag-');
+	});
+
+	it('prefixes the name with an sr-only theme label so colour is never the only cue', () => {
+		render(BucketHeaderChip, { name: 'Krieg', color: 'sienna' });
+		const srOnly = document.querySelector('.sr-only');
+		expect(srOnly?.textContent).toContain(m.timeline_tag_chip_label());
+	});
+
+	it('renders an HTML-bearing name as inert text, never markup (REQ-009)', () => {
+		const evil = '<img src=x onerror="alert(1)">';
+		render(BucketHeaderChip, { name: evil, color: null });
+		expect(document.body.textContent).toContain(evil);
+		expect(document.querySelector('img')).toBeNull();
+	});
+
+	it('paints the label in a fixed ink colour, never the saturated tag token (contrast, REQ-015)', () => {
+		// A saturated --c-tag-* token used as TEXT over its own wash fails 4.5:1 for the
+		// light tokens (amber/sand/sage ≈ 3:1). The tint must go to the background + dot;
+		// the label keeps a guaranteed-contrast ink token.
+		render(BucketHeaderChip, { name: 'Weihnachten', color: 'amber' });
+		const chip = document.querySelector('[data-testid="bucket-header-chip"]') as HTMLElement;
+		expect(chip.getAttribute('style') ?? '').not.toContain('color: var(--c-tag-');
+		const label = document.querySelector('[data-testid="bucket-header-chip-label"]') as HTMLElement;
+		expect(label.className).toContain('text-ink');
+		// still genuinely tinted — the token paints the wash and the dot
+		expect(document.body.innerHTML).toContain('var(--c-tag-amber)');
+	});
+});

frontend/src/lib/timeline/EventPill.svelte

@@ -10,9 +10,11 @@ type TimelineEntryDTO = components['schemas']['TimelineEntryDTO'];
  * Centered axis pill for a derived life-event or a curated PERSONAL event
  * (REQ-007/008). The glyph is wrapped aria-hidden with an sr-only label sibling
  * (REQ-018). An edit affordance shows only for a curated event with an eventId
- * (never derived, never null — REQ-008).
+ * (never derived, never null — REQ-008) and only for a curator who holds
+ * WRITE_ALL (`canWrite`, gate-closed by default — #842 REQ-005/007/008). The
+ * gate is UX only; the real boundary is the #781 route guard + backend permission.
  */
-let { entry }: { entry: TimelineEntryDTO } = $props();
+let { entry, canWrite = false }: { entry: TimelineEntryDTO; canWrite?: boolean } = $props();
 
 const config = $derived(getAccentConfig(entry));
 const dateLabel = $derived(timelineDateLabel(entry.eventDate, entry.precision, entry.eventDateEnd));
@@ -24,7 +26,7 @@ const provenance = $derived(
 // Provenance always shows; the date is an optional prefix so an undated event
 // still reads "abgeleitet"/"kuratiert" (REQ-007).
 const subtitle = $derived(dateLabel ? `${dateLabel} · ${provenance}` : provenance);
-const canEdit = $derived(!entry.derived && entry.eventId != null);
+const canEdit = $derived(canWrite && !entry.derived && entry.eventId != null);
 </script>
 
 <div class="flex justify-center">

frontend/src/lib/timeline/EventPill.svelte.spec.ts

@@ -51,8 +51,9 @@ describe('EventPill', () => {
 		expect(srOnly?.textContent).toBe('Geburt');
 	});
 
-	it('shows an edit affordance for a curated PERSONAL event with an eventId (REQ-008)', () => {
+	it('shows an edit affordance for a curated PERSONAL event when canWrite is true (REQ-005)', () => {
 		render(EventPill, {
+			canWrite: true,
 			entry: makeEntry({
 				kind: 'EVENT',
 				derived: false,
@@ -66,11 +67,45 @@ describe('EventPill', () => {
 		});
 		const edit = document.querySelector('[data-testid="event-edit"]') as HTMLAnchorElement | null;
 		expect(edit).not.toBeNull();
-		expect(edit?.getAttribute('href')).toContain(EVENT_ID);
+		expect(edit?.getAttribute('href')).toBe(`/zeitstrahl/events/${EVENT_ID}/edit`);
 	});
 
-	it('shows no edit affordance when eventId is null (REQ-008)', () => {
+	it('renders no edit affordance for a curated PERSONAL event when canWrite is false (REQ-007)', () => {
 		render(EventPill, {
+			canWrite: false,
+			entry: makeEntry({
+				kind: 'EVENT',
+				derived: false,
+				type: 'PERSONAL',
+				eventId: EVENT_ID,
+				title: 'Auswanderung',
+				senderName: '',
+				receiverName: '',
+				documentId: undefined
+			})
+		});
+		expect(document.querySelector('[data-testid="event-edit"]')).toBeNull();
+	});
+
+	it('renders no edit affordance when the canWrite prop is omitted (gate-closed default) (REQ-007)', () => {
+		render(EventPill, {
+			entry: makeEntry({
+				kind: 'EVENT',
+				derived: false,
+				type: 'PERSONAL',
+				eventId: EVENT_ID,
+				title: 'Auswanderung',
+				senderName: '',
+				receiverName: '',
+				documentId: undefined
+			})
+		});
+		expect(document.querySelector('[data-testid="event-edit"]')).toBeNull();
+	});
+
+	it('shows no edit affordance when eventId is null even with canWrite (REQ-008)', () => {
+		render(EventPill, {
+			canWrite: true,
 			entry: makeEntry({
 				kind: 'EVENT',
 				derived: false,
@@ -85,8 +120,8 @@ describe('EventPill', () => {
 		expect(document.querySelector('[data-testid="event-edit"]')).toBeNull();
 	});
 
-	it('shows no edit affordance for a derived event (REQ-008)', () => {
+	it('shows no edit affordance for a derived event even with canWrite (REQ-008)', () => {
-		render(EventPill, { entry: derived('MARRIAGE', 'Heirat') });
+		render(EventPill, { canWrite: true, entry: derived('MARRIAGE', 'Heirat') });
 		expect(document.querySelector('[data-testid="event-edit"]')).toBeNull();
 	});
 

frontend/src/lib/timeline/GroupingControl.svelte

@@ -0,0 +1,114 @@
+<script lang="ts">
+import * as m from '$lib/paraglide/messages.js';
+import type { GroupingMode } from './timelineGrouping';
+
+/**
+ * The Datum·Ereignis·Thema segmented control (#827, REQ-010/011/018). An ARIA radiogroup with
+ * roving tabindex — single selection, arrow-key navigable — deliberately distinct from #780's
+ * `aria-pressed` layer-filter toggles. Defaults to Datum. Each segment is ≥44×44px, carries a
+ * text label (full word as `aria-label`, an abbreviated label shown ≤360px so the control never
+ * overflows at 320px), and uses semantic tokens so the selected/unselected contrast holds in dark
+ * mode. When `disabled` (the Letters layer is off, nothing to regroup) the control stays in place
+ * — no reflow — keeps its `aria-checked` selection so re-enabling restores the mode, and announces
+ * a screen-reader reason.
+ */
+let {
+	mode = $bindable('date'),
+	disabled = false,
+	ariaLabel = m.timeline_grouping_aria_label()
+}: { mode?: GroupingMode; disabled?: boolean; ariaLabel?: string } = $props();
+
+interface Segment {
+	value: GroupingMode;
+	full: string;
+	short: string;
+}
+
+const segments: Segment[] = [
+	{
+		value: 'date',
+		full: m.timeline_grouping_segment_date(),
+		short: m.timeline_grouping_segment_date_short()
+	},
+	{
+		value: 'event',
+		full: m.timeline_grouping_segment_event(),
+		short: m.timeline_grouping_segment_event_short()
+	},
+	{
+		value: 'thema',
+		full: m.timeline_grouping_segment_thema(),
+		short: m.timeline_grouping_segment_thema_short()
+	}
+];
+
+function select(value: GroupingMode) {
+	if (disabled) return;
+	mode = value;
+}
+
+function onKeydown(event: KeyboardEvent) {
+	if (disabled) return;
+	const forward = event.key === 'ArrowRight' || event.key === 'ArrowDown';
+	const backward = event.key === 'ArrowLeft' || event.key === 'ArrowUp';
+	if (!forward && !backward) return;
+	event.preventDefault();
+	const index = segments.findIndex((s) => s.value === mode);
+	const delta = forward ? 1 : -1;
+	const next = segments[(index + delta + segments.length) % segments.length];
+	mode = next.value;
+	const groupEl = event.currentTarget as HTMLElement;
+	groupEl.querySelector<HTMLElement>(`[data-value="${next.value}"]`)?.focus();
+}
+</script>
+
+<div
+	role="radiogroup"
+	tabindex="-1"
+	aria-label={ariaLabel}
+	aria-disabled={disabled}
+	data-testid="grouping-control"
+	class="inline-flex overflow-hidden rounded-md border border-line"
+	onkeydown={onKeydown}
+>
+	{#each segments as segment (segment.value)}
+		<button
+			type="button"
+			role="radio"
+			data-value={segment.value}
+			aria-label={segment.full}
+			aria-checked={mode === segment.value}
+			tabindex={mode === segment.value ? 0 : -1}
+			disabled={disabled}
+			onclick={() => select(segment.value)}
+			style="display: inline-flex; align-items: center; justify-content: center; min-height: 44px; min-width: 44px"
+			class="px-3 py-2 font-sans text-xs font-semibold focus:outline-none focus-visible:ring-2 focus-visible:ring-brand-navy focus-visible:ring-inset"
+			class:bg-brand-navy={mode === segment.value && !disabled}
+			class:text-white={mode === segment.value && !disabled}
+			class:bg-surface={mode !== segment.value || disabled}
+			class:text-ink-3={mode !== segment.value || disabled}
+		>
+			<span class="seg-full">{segment.full}</span>
+			<span class="seg-short">{segment.short}</span>
+		</button>
+	{/each}
+</div>
+{#if disabled}
+	<span class="sr-only" role="status" data-testid="grouping-disabled-reason"
+		>{m.timeline_grouping_disabled_reason()}</span
+	>
+{/if}
+
+<style>
+.seg-short {
+	display: none;
+}
+@media (max-width: 360px) {
+	.seg-full {
+		display: none;
+	}
+	.seg-short {
+		display: inline;
+	}
+}
+</style>

frontend/src/lib/timeline/GroupingControl.svelte.spec.ts

@@ -0,0 +1,106 @@
+import { describe, it, expect, afterEach } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import { tick } from 'svelte';
+import * as m from '$lib/paraglide/messages.js';
+import GroupingControl from './GroupingControl.svelte';
+
+afterEach(() => cleanup());
+
+const radios = () => Array.from(document.querySelectorAll('[role="radio"]')) as HTMLElement[];
+const group = () => document.querySelector('[role="radiogroup"]') as HTMLElement;
+const checkedValue = () =>
+	radios()
+		.find((r) => r.getAttribute('aria-checked') === 'true')
+		?.getAttribute('data-value');
+
+describe('GroupingControl (REQ-010)', () => {
+	it('renders three radios inside a radiogroup, each with aria-checked (a)', () => {
+		render(GroupingControl, {});
+		expect(group()).not.toBeNull();
+		const r = radios();
+		expect(r).toHaveLength(3);
+		r.forEach((radio) => expect(radio.hasAttribute('aria-checked')).toBe(true));
+	});
+
+	it('defaults to Datum (f)', () => {
+		render(GroupingControl, {});
+		expect(radios().filter((r) => r.getAttribute('aria-checked') === 'true')).toHaveLength(1);
+		expect(checkedValue()).toBe('date');
+	});
+
+	it('exposes a text label on every segment, not colour alone (d)', () => {
+		render(GroupingControl, {});
+		radios().forEach((r) => expect((r.textContent ?? '').trim().length).toBeGreaterThan(0));
+	});
+
+	it('gives the radiogroup an accessible name (e)', () => {
+		render(GroupingControl, {});
+		expect(group().getAttribute('aria-label')).toBe(m.timeline_grouping_aria_label());
+	});
+
+	it('each segment has a tap target of at least 44×44px (c)', () => {
+		render(GroupingControl, {});
+		radios().forEach((r) => {
+			const rect = r.getBoundingClientRect();
+			expect(rect.width).toBeGreaterThanOrEqual(44);
+			expect(rect.height).toBeGreaterThanOrEqual(44);
+		});
+	});
+
+	it('exposes each segment full word as an aria-label (REQ-011)', () => {
+		render(GroupingControl, {});
+		const labels = radios().map((r) => r.getAttribute('aria-label'));
+		expect(labels).toEqual([
+			m.timeline_grouping_segment_date(),
+			m.timeline_grouping_segment_event(),
+			m.timeline_grouping_segment_thema()
+		]);
+	});
+
+	it('moves the selection forward with the right arrow key (b)', async () => {
+		render(GroupingControl, { mode: 'date' });
+		group().dispatchEvent(new KeyboardEvent('keydown', { key: 'ArrowRight', bubbles: true }));
+		await tick();
+		expect(checkedValue()).toBe('event');
+	});
+
+	it('wraps to the last segment with the left arrow from Datum (b)', async () => {
+		render(GroupingControl, { mode: 'date' });
+		group().dispatchEvent(new KeyboardEvent('keydown', { key: 'ArrowLeft', bubbles: true }));
+		await tick();
+		expect(checkedValue()).toBe('thema');
+	});
+
+	it('selects a segment on click', async () => {
+		render(GroupingControl, { mode: 'date' });
+		const thema = radios().find((r) => r.getAttribute('data-value') === 'thema')!;
+		thema.click();
+		await tick();
+		expect(thema.getAttribute('aria-checked')).toBe('true');
+	});
+});
+
+describe('GroupingControl — disabled (REQ-018)', () => {
+	it('marks the radiogroup aria-disabled and keeps all radios in the DOM', () => {
+		render(GroupingControl, { mode: 'event', disabled: true });
+		expect(group().getAttribute('aria-disabled')).toBe('true');
+		expect(radios()).toHaveLength(3);
+	});
+
+	it('announces a screen-reader reason that letters are hidden', () => {
+		render(GroupingControl, { disabled: true });
+		const reason = document.querySelector('[data-testid="grouping-disabled-reason"]');
+		expect(reason?.textContent).toContain(m.timeline_grouping_disabled_reason());
+	});
+
+	it('retains the active mode while disabled (no reset to Datum)', () => {
+		render(GroupingControl, { mode: 'thema', disabled: true });
+		expect(checkedValue()).toBe('thema');
+	});
+
+	it('ignores arrow keys while disabled', () => {
+		render(GroupingControl, { mode: 'event', disabled: true });
+		group().dispatchEvent(new KeyboardEvent('keydown', { key: 'ArrowRight', bubbles: true }));
+		expect(checkedValue()).toBe('event');
+	});
+});

frontend/src/lib/timeline/LetterBucket.svelte

@@ -0,0 +1,195 @@
+<script lang="ts">
+import * as m from '$lib/paraglide/messages.js';
+import LetterCard from './LetterCard.svelte';
+import BucketHeaderChip from './BucketHeaderChip.svelte';
+import { entryKey } from './entryKey';
+import { getAccentConfig } from './eventCardConfig';
+import { timelineDateLabel } from './dateLabel';
+import { CLUSTER_PREVIEW, tagColorVar, type LetterBucket } from './timelineGrouping';
+import type { components } from '$lib/generated/api';
+
+type TimelineEntryDTO = components['schemas']['TimelineEntryDTO'];
+
+/**
+ * One cluster of loose letters, bound together by a coloured left rail so the group reads as a
+ * unit (#827). The axis-fixed world-band layer is rendered elsewhere — this is only the
+ * loose-letter bundling.
+ *
+ * - Thema: a tinted root-tag header chip + a rail in the tag colour, over compact cards whose own
+ *   tag chip is suppressed (REQ-004/015/017).
+ * - Ereignis: a same-year curated `event` becomes the card header (glyph, title, date,
+ *   provenance, edit pencil) so its title reads once — no separate floating pill (#827 redesign,
+ *   REQ-001/014). A cross-year cluster keeps a plain text header. The standalone "Weitere Briefe"
+ *   / "Ohne Thema" fallback keeps its label and a neutral dashed rail (REQ-006/007).
+ *
+ * A cluster shows its first `CLUSTER_PREVIEW` letters, then a show-more toggle reveals the rest
+ * instead of flooding the timeline with every card (#827 redesign).
+ */
+let {
+	bucket,
+	mode,
+	// `year` is the band's year — accepted for the cross-year label card seam (#827) but no
+	// longer consumed here now the in-bucket month-density strip is gone (the year frames the
+	// time from the band heading). Kept in the prop contract for callers/tests.
+	// eslint-disable-next-line @typescript-eslint/no-unused-vars
+	year = 0,
+	nested = false,
+	event = undefined,
+	canWrite = false
+}: {
+	bucket: LetterBucket;
+	mode: 'event' | 'thema';
+	year?: number;
+	nested?: boolean;
+	/** The same-year curated event whose letters this card holds — renders as the header. */
+	event?: TimelineEntryDTO;
+	canWrite?: boolean;
+} = $props();
+
+const count = $derived(bucket.letters.length);
+const fallbackLabel = $derived(
+	mode === 'event' ? m.timeline_bucket_other_letters() : m.timeline_bucket_no_topic()
+);
+
+// Event-as-header (#827 redesign): a same-year curated event renders as this card's header,
+// mirroring EventPill — glyph + title + date · provenance + an edit pencil for a curator. The
+// title is never repeated as a separate floating pill.
+const accent = $derived(event ? getAccentConfig(event) : null);
+const eventDateLabel = $derived(
+	event ? timelineDateLabel(event.eventDate, event.precision, event.eventDateEnd) : null
+);
+const provenance = $derived(
+	event?.derived ? m.timeline_provenance_derived() : m.timeline_provenance_curated()
+);
+const eventSubtitle = $derived(eventDateLabel ? `${eventDateLabel} · ${provenance}` : provenance);
+const canEdit = $derived(canWrite && !!event && !event.derived && event.eventId != null);
+// The left rail binds the cluster: the tag colour in Thema, mint for an Ereignis cluster,
+// neutral for the fallback (and for a colourless/unknown tag token).
+const railColor = $derived(bucket.kind === 'tag' ? tagColorVar(bucket.color) : null);
+const railStyle = $derived(railColor ? `border-left-color: ${railColor}` : '');
+const isEventCluster = $derived(nested || bucket.kind === 'event');
+const cardVariant = $derived(mode === 'event' && isEventCluster ? 'event' : 'plain');
+
+// First-5 preview + show-more (#827 redesign): a large cluster stays readable instead of
+// dumping every card into the timeline.
+let expanded = $state(false);
+const visible = $derived(expanded ? bucket.letters : bucket.letters.slice(0, CLUSTER_PREVIEW));
+const hiddenCount = $derived(bucket.letters.length - CLUSTER_PREVIEW);
+
+// The catch-all "Weitere Briefe" / "Ohne Thema" bin is a junk drawer: render it count-only
+// behind a reveal control so it never floods the timeline; every other cluster starts open
+// (#827 redesign). The view re-creates a bucket per `{#each}` key, so the initial capture is
+// the right lifetime — `revealed` belongs to this bucket instance.
+const isDrawer = $derived(bucket.kind === 'fallback');
+// svelte-ignore state_referenced_locally
+let revealed = $state(bucket.kind !== 'fallback');
+</script>
+
+<section
+	class="my-3 overflow-hidden rounded-md border border-l-2 border-line bg-surface shadow-sm"
+	class:border-l-brand-mint={isEventCluster}
+	class:border-dashed={isDrawer}
+	style={railStyle}
+	data-testid="letter-bucket"
+	data-bucket-kind={bucket.kind}
+>
+	{#if !nested}
+		{#if event && accent}
+			<!-- A same-year curated event IS the card header — its title reads once here, never
+			     also as a floating pill (#827 redesign, REQ-001/014). Glyph is aria-hidden with an
+			     sr-only label sibling (REQ-018); the edit pencil mirrors EventPill's gate. -->
+			<header
+				data-testid="bucket-event-header"
+				class="flex items-center gap-2 border-b border-line bg-canvas px-3 py-2"
+			>
+				<span
+					class="flex h-7 w-7 shrink-0 items-center justify-center rounded-full {accent.accent ===
+					'curated'
+						? 'bg-brand-mint text-brand-navy'
+						: 'bg-brand-navy text-brand-mint'}"
+				>
+					<span aria-hidden="true">{accent.glyph}</span>
+					<span class="sr-only">{accent.label}</span>
+				</span>
+				<span class="min-w-0 text-left">
+					<span class="block font-serif text-sm font-bold whitespace-pre-line text-brand-navy"
+						>{event.title}</span
+					>
+					<span class="block font-sans text-xs text-ink-3">
+						{eventSubtitle} <span data-testid="bucket-count">· {count}</span>
+					</span>
+				</span>
+				{#if canEdit}
+					<a
+						data-testid="event-edit"
+						href="/zeitstrahl/events/{event.eventId}/edit"
+						class="ml-auto rounded-sm px-1 font-sans text-xs text-ink-3 hover:text-brand-navy focus:outline-none focus-visible:ring-2 focus-visible:ring-brand-navy"
+					>
+						<span aria-hidden="true">✎</span>
+						<span class="sr-only">{m.btn_edit()}</span>
+					</a>
+				{/if}
+			</header>
+		{:else}
+			<header
+				class="flex items-center gap-2 px-3 py-2"
+				class:bg-canvas={isEventCluster}
+				class:border-b={!isDrawer}
+				class:border-line={!isDrawer}
+			>
+				{#if mode === 'thema' && bucket.kind === 'tag'}
+					<BucketHeaderChip name={bucket.title ?? ''} color={bucket.color} />
+				{:else if mode === 'event' && bucket.kind === 'event'}
+					<span class="font-serif text-sm font-bold text-ink">
+						<span aria-hidden="true">✉</span>
+						{bucket.title}
+					</span>
+				{:else}
+					<span class="font-sans text-xs font-semibold text-ink-3">{fallbackLabel}</span>
+				{/if}
+				<span data-testid="bucket-count" class="font-sans text-xs text-ink-3">· {count}</span>
+			</header>
+		{/if}
+	{/if}
+
+	<div class="px-3 py-2">
+		{#if !revealed}
+			<button
+				type="button"
+				data-testid="bucket-reveal"
+				onclick={() => (revealed = true)}
+				style="display: inline-flex; align-items: center; min-height: 44px"
+				class="px-1 font-sans text-xs font-semibold text-brand-navy hover:underline focus:outline-none focus-visible:ring-2 focus-visible:ring-brand-navy"
+			>
+				{m.timeline_bucket_show_more({ count: bucket.letters.length })}
+			</button>
+		{:else}
+			<ul class="space-y-1.5">
+				{#each visible as letter (entryKey(letter))}
+					<li>
+						<LetterCard
+							entry={letter}
+							variant={cardVariant}
+							suppressTagChip={mode === 'thema'}
+							compact={true}
+						/>
+					</li>
+				{/each}
+			</ul>
+			{#if hiddenCount > 0}
+				<button
+					type="button"
+					data-testid="bucket-show-more"
+					aria-expanded={expanded}
+					onclick={() => (expanded = !expanded)}
+					style="display: inline-flex; align-items: center; min-height: 44px"
+					class="mt-1 px-1 font-sans text-xs font-semibold text-brand-navy hover:underline focus:outline-none focus-visible:ring-2 focus-visible:ring-brand-navy"
+				>
+					{expanded
+						? m.timeline_bucket_show_less()
+						: m.timeline_bucket_show_more({ count: hiddenCount })}
+				</button>
+			{/if}
+		{/if}
+	</div>
+</section>

frontend/src/lib/timeline/LetterBucket.svelte.spec.ts

@@ -0,0 +1,232 @@
+import { describe, it, expect, afterEach } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import { tick } from 'svelte';
+import * as m from '$lib/paraglide/messages.js';
+import LetterBucket from './LetterBucket.svelte';
+import { makeEntry } from './test-factories';
+import type { LetterBucket as Bucket } from './timelineGrouping';
+
+afterEach(() => cleanup());
+
+const eventBucket: Bucket = {
+	key: 'event:e1',
+	kind: 'event',
+	title: 'Briefe von der Front',
+	color: null,
+	letters: [makeEntry({ documentId: 'a' }), makeEntry({ documentId: 'b' })]
+};
+
+const tagBucket: Bucket = {
+	key: 'tag:t1',
+	kind: 'tag',
+	title: 'Krieg',
+	color: 'sienna',
+	letters: [makeEntry({ documentId: 'c', rootTagName: 'Krieg', rootTagColor: 'sienna' })]
+};
+
+describe('LetterBucket — Ereignis mode (REQ-003/006/014)', () => {
+	it('shows the event title and the cluster count', () => {
+		render(LetterBucket, { bucket: eventBucket, mode: 'event' });
+		expect(document.body.textContent).toContain('Briefe von der Front');
+		expect(document.querySelector('[data-testid="bucket-count"]')?.textContent).toContain('2');
+	});
+
+	it('renders its letters as .lcard.ev event cards (REQ-014)', () => {
+		render(LetterBucket, { bucket: eventBucket, mode: 'event' });
+		expect(document.querySelectorAll('a.lcard.ev')).toHaveLength(2);
+	});
+
+	it('uses the localized "Weitere Briefe" label and plain cards for the fallback bucket (REQ-006)', () => {
+		const fb: Bucket = {
+			key: '__fallback__',
+			kind: 'fallback',
+			color: null,
+			letters: [makeEntry({ documentId: 'x' })]
+		};
+		render(LetterBucket, { bucket: fb, mode: 'event' });
+		expect(document.body.textContent).toContain(m.timeline_bucket_other_letters());
+		// fallback letters are not clustered under a curated event → plain card, never .lcard.ev
+		expect(document.querySelector('a.ev')).toBeNull();
+	});
+});
+
+describe('LetterBucket — Thema mode (REQ-004/007/015/017)', () => {
+	it('renders a tinted bucket-header chip carrying the root-tag name (REQ-015)', () => {
+		render(LetterBucket, { bucket: tagBucket, mode: 'thema' });
+		const chip = document.querySelector('[data-testid="bucket-header-chip"]');
+		expect(chip?.textContent).toContain('Krieg');
+	});
+
+	it('suppresses the per-letter tag chip inside its own root-tag bucket (REQ-017)', () => {
+		render(LetterBucket, { bucket: tagBucket, mode: 'thema' });
+		expect(document.querySelector('[data-testid="tag-chip"]')).toBeNull();
+	});
+
+	it('uses the localized "Ohne Thema" label for the untagged fallback bucket (REQ-007)', () => {
+		const fb: Bucket = {
+			key: '__fallback__',
+			kind: 'fallback',
+			color: null,
+			letters: [makeEntry({ documentId: 'y', rootTagName: undefined })]
+		};
+		render(LetterBucket, { bucket: fb, mode: 'thema' });
+		expect(document.body.textContent).toContain(m.timeline_bucket_no_topic());
+	});
+});
+
+const manyLetters = (n: number) =>
+	Array.from({ length: n }, (_, i) =>
+		makeEntry({ documentId: `d${i}`, eventDate: `1916-0${(i % 9) + 1}-01` })
+	);
+
+describe('LetterBucket — preview cap + show-more (#827 redesign)', () => {
+	it('shows only the first 5 letters with a show-more toggle when the cluster is larger', () => {
+		const bucket: Bucket = {
+			key: 'tag:t1',
+			kind: 'tag',
+			title: 'Krieg',
+			color: 'sienna',
+			letters: manyLetters(8)
+		};
+		render(LetterBucket, { bucket, mode: 'thema', year: 1916 });
+		expect(document.querySelectorAll('a.lcard')).toHaveLength(5);
+		expect(document.querySelector('[data-testid="bucket-show-more"]')).not.toBeNull();
+		expect(document.querySelector('[data-testid="strip-expand"]')).toBeNull(); // sparkline gone
+	});
+
+	it('expands to all letters and collapses back on toggle', async () => {
+		const bucket: Bucket = {
+			key: 'tag:t1',
+			kind: 'tag',
+			title: 'Krieg',
+			color: 'sienna',
+			letters: manyLetters(8)
+		};
+		render(LetterBucket, { bucket, mode: 'thema', year: 1916 });
+		(document.querySelector('[data-testid="bucket-show-more"]') as HTMLButtonElement).click();
+		await tick();
+		expect(document.querySelectorAll('a.lcard')).toHaveLength(8);
+		(document.querySelector('[data-testid="bucket-show-more"]') as HTMLButtonElement).click();
+		await tick();
+		expect(document.querySelectorAll('a.lcard')).toHaveLength(5);
+	});
+
+	it('shows all letters and no toggle for a small cluster (<= 5)', () => {
+		const bucket: Bucket = {
+			key: 'tag:t1',
+			kind: 'tag',
+			title: 'Tod',
+			color: null,
+			letters: manyLetters(3)
+		};
+		render(LetterBucket, { bucket, mode: 'thema', year: 1916 });
+		expect(document.querySelectorAll('a.lcard')).toHaveLength(3);
+		expect(document.querySelector('[data-testid="bucket-show-more"]')).toBeNull();
+	});
+
+	it('binds a tag bucket together with a coloured left rail from its token', () => {
+		const bucket: Bucket = {
+			key: 'tag:t1',
+			kind: 'tag',
+			title: 'Krieg',
+			color: 'sienna',
+			letters: manyLetters(1)
+		};
+		render(LetterBucket, { bucket, mode: 'thema', year: 1916 });
+		const section = document.querySelector('[data-testid="letter-bucket"]') as HTMLElement;
+		expect(section.getAttribute('style') ?? '').toContain('var(--c-tag-sienna)');
+	});
+});
+
+describe('LetterBucket — leftover drawer (#827 redesign)', () => {
+	const fb = (n: number): Bucket => ({
+		key: '__fallback__',
+		kind: 'fallback',
+		color: null,
+		letters: Array.from({ length: n }, (_, i) =>
+			makeEntry({ documentId: `f${i}`, eventDate: `1916-01-0${(i % 9) + 1}` })
+		)
+	});
+	it('renders collapsed — count + reveal, no letter cards — until opened', () => {
+		render(LetterBucket, { bucket: fb(20), mode: 'event', year: 1916 });
+		expect(document.querySelector('a.lcard')).toBeNull();
+		expect(document.body.textContent).toContain(m.timeline_bucket_other_letters());
+		expect(document.querySelector('[data-testid="bucket-reveal"]')).not.toBeNull();
+	});
+	it('reveals the first 5 letters when opened', async () => {
+		render(LetterBucket, { bucket: fb(20), mode: 'event', year: 1916 });
+		(document.querySelector('[data-testid="bucket-reveal"]') as HTMLButtonElement).click();
+		await tick();
+		expect(document.querySelectorAll('a.lcard')).toHaveLength(5);
+		expect(document.querySelector('[data-testid="bucket-show-more"]')).not.toBeNull();
+	});
+});
+
+describe('LetterBucket — card chrome (#827 redesign)', () => {
+	it('renders the cluster as a contained card (bordered, rounded, surface)', () => {
+		const bucket: Bucket = {
+			key: 'tag:t1',
+			kind: 'tag',
+			title: 'Krieg',
+			color: 'sienna',
+			letters: [makeEntry({ documentId: 'a' })]
+		};
+		render(LetterBucket, { bucket, mode: 'thema', year: 1916 });
+		const card = document.querySelector('[data-testid="letter-bucket"]') as HTMLElement;
+		expect(card.className).toMatch(/\brounded\b|rounded-/);
+		expect(card.className).toContain('border');
+		expect(card.className).toContain('bg-surface');
+	});
+});
+
+describe('LetterBucket — event-as-header (#827 redesign)', () => {
+	it('renders the curated event as the card header when given an `event` (no separate pill)', () => {
+		const event = makeEntry({
+			kind: 'EVENT',
+			type: 'PERSONAL',
+			derived: false,
+			eventId: 'e1',
+			title: 'Ein gewaltiger Stadtbrand',
+			eventDate: '1916-07-06',
+			senderName: '',
+			receiverName: '',
+			documentId: undefined
+		});
+		const bucket: Bucket = {
+			key: 'event:e1',
+			kind: 'event',
+			title: 'Ein gewaltiger Stadtbrand',
+			color: null,
+			letters: [makeEntry({ documentId: 'a', linkedEventId: 'e1' })]
+		};
+		render(LetterBucket, { bucket, mode: 'event', year: 1916, event, canWrite: true });
+		const header = document.querySelector('[data-testid="bucket-event-header"]') as HTMLElement;
+		expect(header.textContent).toContain('Ein gewaltiger Stadtbrand');
+		expect(header.textContent).toContain(m.timeline_provenance_curated());
+		expect(document.querySelector('[data-testid="event-edit"]')?.getAttribute('href')).toBe(
+			'/zeitstrahl/events/e1/edit'
+		);
+	});
+
+	it('shows no edit affordance in the header when canWrite is false', () => {
+		const event = makeEntry({
+			kind: 'EVENT',
+			type: 'PERSONAL',
+			derived: false,
+			eventId: 'e1',
+			title: 'X',
+			senderName: '',
+			receiverName: '',
+			documentId: undefined
+		});
+		const bucket: Bucket = {
+			key: 'event:e1',
+			kind: 'event',
+			title: 'X',
+			color: null,
+			letters: [makeEntry({ documentId: 'a' })]
+		};
+		render(LetterBucket, { bucket, mode: 'event', year: 1916, event, canWrite: false });
+		expect(document.querySelector('[data-testid="event-edit"]')).toBeNull();
+	});
+});

frontend/src/lib/timeline/LetterCard.svelte

@@ -12,10 +12,30 @@ type TimelineEntryDTO = components['schemas']['TimelineEntryDTO'];
  * precision-aware date chip, linking to the document. Names/titles are
  * OCR/import-derived — rendered via default `{...}` escaping with
  * `whitespace-pre-line` for line breaks (REQ-021); never the raw-HTML directive.
+ *
+ * In Ereignis mode the card sits inside an event cluster and renders as the
+ * `.lcard.ev` variant (#827, REQ-014). In Thema mode the per-letter tag chip is
+ * suppressed inside its own root-tag bucket, where the bucket header already
+ * carries the topic (`suppressTagChip`, REQ-017).
  */
-let { entry }: { entry: TimelineEntryDTO } = $props();
+let {
+	entry,
+	variant = 'plain',
+	suppressTagChip = false,
+	compact = false
+}: {
+	entry: TimelineEntryDTO;
+	variant?: 'plain' | 'event';
+	suppressTagChip?: boolean;
+	compact?: boolean;
+} = $props();
 
+const isEventVariant = $derived(variant === 'event');
 const dateLabel = $derived(timelineDateLabel(entry.eventDate, entry.precision, entry.eventDateEnd));
+// Inside a per-year bucket the year frames the time, and these archive titles already
+// embed the date — so the compact in-bucket card drops the redundant date chip when a
+// title is present, halving the row height and killing the duplicate date (#827).
+const showDate = $derived(!compact || !entry.title);
 const sender = $derived(entry.senderName === '' ? m.timeline_unknown_person() : entry.senderName);
 const receiver = $derived(
 	entry.receiverName === '' ? m.timeline_unknown_person() : entry.receiverName
@@ -28,28 +48,37 @@ const receiver = $derived(
 <a
 	href="/documents/{entry.documentId}"
 	style="display: flex; flex-direction: column; justify-content: center; min-height: 44px"
-	class="rounded-sm border border-l-[3px] border-line border-l-brand-mint bg-surface px-3 py-2 shadow-sm transition-colors hover:border-brand-mint focus:outline-none focus-visible:ring-2 focus-visible:ring-brand-navy"
+	class="lcard rounded-sm border border-l-[3px] border-line border-l-brand-mint bg-surface px-3 shadow-sm transition-colors hover:border-brand-mint focus:outline-none focus-visible:ring-2 focus-visible:ring-brand-navy"
+	class:py-2={!compact}
+	class:py-1={compact}
+	class:ev={isEventVariant}
+	class:compact={compact}
 >
 	{#if entry.title}
 		<!-- ✉ + sr-only label are static chrome rendered as sibling nodes, NEVER
 		     interpolated into the escaped user title; the title keeps its own
 		     pre-line span for multi-line OCR text (REQ-008/016/021). -->
-		<span class="font-serif text-sm font-bold break-words text-ink">
+		<span
+			class="font-serif font-bold break-words text-ink"
+			class:text-sm={!compact}
+			class:text-xs={compact}
+		>
 			<GlyphLabel glyph="✉" label={m.timeline_letter_glyph_label()} />
 			<span class="whitespace-pre-line">{entry.title}</span>
 		</span>
 	{/if}
-	<span class="mt-0.5 font-sans text-xs break-words text-ink-3">
+	<span class="font-sans text-xs break-words text-ink-3" class:mt-0.5={!compact}>
 		<span class="font-serif whitespace-pre-line">{sender}</span>
 		<span aria-hidden="true">→</span>
 		<span class="font-serif whitespace-pre-line">{receiver}</span>
-		{#if dateLabel}
+		{#if dateLabel && showDate}
 			<span data-testid="letter-date"> · {dateLabel}</span>
 		{/if}
 	</span>
-	{#if entry.rootTagName}
+	{#if entry.rootTagName && !suppressTagChip}
 		<!-- The primary root-tag chip sits on its own line beneath the meta line
-		     (#835 §3); absent when the letter has no tag (REQ-005). -->
+		     (#835 §3); absent when the letter has no tag (REQ-005), and suppressed in
+		     Thema mode inside its own root-tag bucket where the header conveys it (REQ-017). -->
 		<TagChip name={entry.rootTagName} color={entry.rootTagColor ?? null} />
 	{/if}
 </a>

frontend/src/lib/timeline/LetterCard.svelte.spec.ts

@@ -127,3 +127,46 @@ describe('LetterCard', () => {
 		expect(chip?.textContent).toContain('Familie');
 	});
 });
+
+describe('LetterCard — grouping variants (#827, REQ-014/017)', () => {
+	it('carries the .lcard.ev class in the event variant (REQ-014)', () => {
+		render(LetterCard, { entry: makeEntry(), variant: 'event' });
+		expect(document.querySelector('a.lcard.ev')).not.toBeNull();
+	});
+
+	it('is a plain card with no .ev marker by default (REQ-014)', () => {
+		render(LetterCard, { entry: makeEntry() });
+		expect(document.querySelector('a.ev')).toBeNull();
+	});
+
+	it('suppresses the per-letter tag chip when asked, even with a root tag (REQ-017)', () => {
+		render(LetterCard, {
+			entry: makeEntry({ rootTagName: 'Krieg', rootTagColor: 'sienna' }),
+			suppressTagChip: true
+		});
+		expect(document.querySelector('[data-testid="tag-chip"]')).toBeNull();
+	});
+
+	it('still shows the per-letter tag chip when not suppressed — Datum/Ereignis (REQ-017)', () => {
+		render(LetterCard, { entry: makeEntry({ rootTagName: 'Krieg', rootTagColor: 'sienna' }) });
+		expect(document.querySelector('[data-testid="tag-chip"]')).not.toBeNull();
+	});
+
+	it('drops the redundant date line in the compact variant when a title is present (#827)', () => {
+		// Inside a per-year bucket the year already frames the time, and these archive
+		// titles embed the date — so the compact in-bucket card omits the date chip.
+		render(LetterCard, { entry: makeEntry({ title: 'H-0023 – 6. Juli 1916' }), compact: true });
+		expect(document.querySelector('[data-testid="letter-date"]')).toBeNull();
+		expect(document.body.textContent).toContain('Karl Raddatz'); // sender still shown
+	});
+
+	it('keeps the date in the compact variant when the letter has no title (#827)', () => {
+		render(LetterCard, { entry: makeEntry({ title: undefined }), compact: true });
+		expect(document.querySelector('[data-testid="letter-date"]')).not.toBeNull();
+	});
+
+	it('renders the compact variant on a single tighter row (#827)', () => {
+		render(LetterCard, { entry: makeEntry(), compact: true });
+		expect(document.querySelector('a.lcard.compact')).not.toBeNull();
+	});
+});

frontend/src/lib/timeline/TimelineFilters.svelte

@@ -0,0 +1,133 @@
+<script lang="ts">
+import * as m from '$lib/paraglide/messages.js';
+import { slide } from 'svelte/transition';
+import { hiddenLayerCount, isDefaultState, type TimelineLayerFilters } from './timelineFilter';
+
+// Presentation-only layer filter for the global /zeitstrahl (#780, REQ-001).
+// Holds no timeline data and never navigates or fetches — the route owns the
+// $state and derives the filtered view. Three $bindable layer booleans plus an
+// onChange notification hook are the whole contract.
+let {
+	personalOn = $bindable(true),
+	historicalOn = $bindable(true),
+	lettersOn = $bindable(true),
+	onChange
+}: {
+	personalOn?: boolean;
+	historicalOn?: boolean;
+	lettersOn?: boolean;
+	onChange?: () => void;
+} = $props();
+
+let open = $state(false);
+
+// Reuse the reduced-motion guard expression from documents/[id]/+page.svelte:57
+// for a new purpose — zeroing the slide duration so the collapsible opens
+// instantly when the reader prefers reduced motion (REQ-009).
+const prefersReducedMotion = $derived(
+	typeof window !== 'undefined' && window.matchMedia('(prefers-reduced-motion: reduce)').matches
+);
+const slideDuration = $derived(prefersReducedMotion ? 0 : 200);
+
+const filters: TimelineLayerFilters = $derived({ personalOn, historicalOn, lettersOn });
+const hiddenCount = $derived(hiddenLayerCount(filters));
+const anyLayerOff = $derived(!isDefaultState(filters));
+
+function reset() {
+	personalOn = true;
+	historicalOn = true;
+	lettersOn = true;
+	onChange?.();
+}
+</script>
+
+{#snippet layerToggle(label: string, testid: string, pressed: boolean, toggle: () => void)}
+	<button
+		type="button"
+		data-testid={testid}
+		aria-pressed={pressed}
+		onclick={toggle}
+		class="inline-flex min-h-[44px] items-center gap-2 rounded border px-3 font-sans text-sm transition-colors {pressed
+			? 'border-primary bg-primary text-primary-fg'
+			: 'border-line bg-muted text-ink-2 hover:bg-line'}"
+	>
+		<span
+			aria-hidden="true"
+			class="inline-flex h-4 w-4 items-center justify-center rounded-sm border {pressed
+				? 'border-primary-fg bg-primary-fg/20'
+				: 'border-ink-3'}"
+		>
+			{#if pressed}✓{/if}
+		</span>
+		{label}
+	</button>
+{/snippet}
+
+<section class="mb-6">
+	<!-- Sticky trigger kept in document flow so the hidden-layer count stays
+	     visible without clipping timeline content (REQ-007). -->
+	<div class="sticky top-16 z-20 bg-canvas py-2">
+		<button
+			type="button"
+			data-testid="timeline-filter-trigger"
+			aria-expanded={open}
+			aria-controls={open ? 'timeline-filter-panel' : undefined}
+			onclick={() => (open = !open)}
+			class="inline-flex min-h-[44px] items-center gap-2 rounded border border-line bg-surface px-4 font-sans text-xs font-bold tracking-widest text-ink-2 uppercase transition-colors hover:bg-muted"
+		>
+			{hiddenCount === 0
+				? m.timeline_filter_trigger()
+				: m.timeline_filter_trigger_active({ count: hiddenCount })}
+		</button>
+	</div>
+
+	{#if open}
+		<div id="timeline-filter-panel" transition:slide={{ duration: slideDuration }}>
+			<fieldset class="mt-2 rounded-sm border border-line bg-surface p-4">
+				<legend class="px-1 font-sans text-xs font-bold tracking-widest text-ink-3 uppercase">
+					{m.timeline_filter_label_layers()}
+				</legend>
+				<div class="flex flex-wrap gap-2">
+					{@render layerToggle(
+						m.timeline_filter_layer_personal(),
+						'timeline-filter-personal',
+						personalOn,
+						() => {
+							personalOn = !personalOn;
+							onChange?.();
+						}
+					)}
+					{@render layerToggle(
+						m.timeline_filter_layer_historical(),
+						'timeline-filter-historical',
+						historicalOn,
+						() => {
+							historicalOn = !historicalOn;
+							onChange?.();
+						}
+					)}
+					{@render layerToggle(
+						m.timeline_filter_layer_letters(),
+						'timeline-filter-letters',
+						lettersOn,
+						() => {
+							lettersOn = !lettersOn;
+							onChange?.();
+						}
+					)}
+				</div>
+
+				{#if anyLayerOff}
+					<button
+						type="button"
+						data-testid="timeline-filter-reset"
+						onclick={reset}
+						class="mt-3 inline-flex min-h-[44px] items-center font-sans text-sm text-primary underline-offset-2 hover:underline"
+					>
+						{m.timeline_filter_reset()}
+					</button>
+				{/if}
+			</fieldset>
+		</div>
+	{/if}
+</section>

frontend/src/lib/timeline/TimelineFilters.svelte.spec.ts

@@ -0,0 +1,74 @@
+import { describe, it, expect, vi, afterEach } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import { page } from 'vitest/browser';
+import * as m from '$lib/paraglide/messages.js';
+import TimelineFilters from './TimelineFilters.svelte';
+
+afterEach(() => cleanup());
+
+const allOn = () => ({ personalOn: true, historicalOn: true, lettersOn: true, onChange: vi.fn() });
+
+async function openBar() {
+	await page.getByTestId('timeline-filter-trigger').click();
+}
+
+describe('TimelineFilters', () => {
+	it('renders the three layer toggles with accessible names inside a labelled group (REQ-001)', async () => {
+		render(TimelineFilters, allOn());
+		await openBar();
+		await expect
+			.element(page.getByRole('button', { name: m.timeline_filter_layer_personal() }))
+			.toBeVisible();
+		await expect
+			.element(page.getByRole('button', { name: m.timeline_filter_layer_historical() }))
+			.toBeVisible();
+		await expect
+			.element(page.getByRole('button', { name: m.timeline_filter_layer_letters() }))
+			.toBeVisible();
+		// the fieldset legend groups the toggles
+		await expect.element(page.getByText(m.timeline_filter_label_layers())).toBeVisible();
+	});
+
+	it('reflects a layer as pressed and flips it, firing onChange (REQ-001)', async () => {
+		const props = allOn();
+		render(TimelineFilters, props);
+		await openBar();
+		const personal = page.getByTestId('timeline-filter-personal');
+		await expect.element(personal).toHaveAttribute('aria-pressed', 'true');
+		await personal.click();
+		await expect.element(personal).toHaveAttribute('aria-pressed', 'false');
+		expect(props.onChange).toHaveBeenCalled();
+	});
+
+	it('shows a plain trigger when all layers are on and a count once a layer is hidden (REQ-007/010)', async () => {
+		render(TimelineFilters, allOn());
+		const trigger = page.getByTestId('timeline-filter-trigger');
+		await expect.element(trigger).toHaveTextContent(m.timeline_filter_trigger());
+		await expect.element(trigger).not.toHaveTextContent('aktiv');
+		await trigger.click();
+		await page.getByTestId('timeline-filter-letters').click();
+		await expect.element(trigger).toHaveTextContent(m.timeline_filter_trigger_active({ count: 1 }));
+	});
+
+	it('gives the trigger a 44px touch target (REQ-007)', async () => {
+		render(TimelineFilters, allOn());
+		await expect.element(page.getByTestId('timeline-filter-trigger')).toHaveClass(/min-h-\[44px\]/);
+	});
+
+	it('hides the reset button by default and restores all layers when activated (REQ-008)', async () => {
+		const props = allOn();
+		render(TimelineFilters, props);
+		await openBar();
+		const reset = page.getByTestId('timeline-filter-reset');
+		// absent (not just hidden) while every layer is on
+		expect(reset.query()).toBeNull();
+		await page.getByTestId('timeline-filter-historical').click();
+		await expect.element(reset).toBeVisible();
+		await reset.click();
+		await expect
+			.element(page.getByTestId('timeline-filter-historical'))
+			.toHaveAttribute('aria-pressed', 'true');
+		await expect.poll(() => reset.query()).toBeNull();
+		expect(props.onChange).toHaveBeenCalled();
+	});
+});

frontend/src/lib/timeline/TimelineView.svelte

@@ -6,6 +6,7 @@ import LetterCard from './LetterCard.svelte';
 import EventPill from './EventPill.svelte';
 import WorldBand from './WorldBand.svelte';
 import { entryKey } from './entryKey';
+import { buildEventLookup, type GroupingMode } from './timelineGrouping';
 import type { components } from '$lib/generated/api';
 
 type TimelineDTO = components['schemas']['TimelineDTO'];
@@ -18,8 +19,28 @@ type TimelineYearDTO = components['schemas']['TimelineYearDTO'];
  * empty timeline shows a calm message (REQ-017). `personId` is a declared seam
  * for the per-person rail (issue #10) and is undefined here; it is not passed to
  * leaf cards (REQ-025). Owns no <main> — the layout does.
+ *
+ * `groupingMode` (#827) flows down to each YearBand to re-bundle its loose letters;
+ * the event lookup — the curated events present in this (already layer-filtered)
+ * view — is resolved once here so Ereignis clusters never reference a filtered-out
+ * event (filter-then-group, REQ-019). The undated bucket renders unchanged in every
+ * mode (its letters have no year, so the per-year bucketing does not apply).
  */
-let { timeline, personId = undefined }: { timeline: TimelineDTO; personId?: string } = $props();
+let {
+	timeline,
+	personId = undefined,
+	canWrite = false,
+	groupingMode = 'date'
+}: {
+	timeline: TimelineDTO;
+	personId?: string;
+	canWrite?: boolean;
+	groupingMode?: GroupingMode;
+} = $props();
+
+const eventLookup = $derived(
+	groupingMode === 'date' ? new Map<string, string>() : buildEventLookup(timeline)
+);
 
 type Row = { t: 'band'; year: TimelineYearDTO } | { t: 'gap'; from: number; to: number };
 
@@ -50,7 +71,12 @@ const isEmpty = $derived(timeline.years.length === 0 && timeline.undated.length
 		{#each rows as row (row.t === 'band' ? `band-${row.year.year}` : `gap-${row.from}`)}
 			<li>
 				{#if row.t === 'band'}
-					<YearBand year={row.year} />
+					<YearBand
+						year={row.year}
+						canWrite={canWrite}
+						groupingMode={groupingMode}
+						eventLookup={eventLookup}
+					/>
 				{:else}
 					<GapSpan from={row.from} to={row.to} />
 				{/if}
@@ -75,9 +101,9 @@ const isEmpty = $derived(timeline.years.length === 0 && timeline.undated.length
 					<li>
 						{#if entry.kind === 'EVENT'}
 							{#if entry.type === 'HISTORICAL'}
-								<WorldBand entry={entry} />
+								<WorldBand entry={entry} canWrite={canWrite} />
 							{:else}
-								<EventPill entry={entry} />
+								<EventPill entry={entry} canWrite={canWrite} />
 							{/if}
 						{:else}
 							<LetterCard entry={entry} />

frontend/src/lib/timeline/TimelineView.svelte.spec.ts

@@ -105,6 +105,7 @@ describe('TimelineView', () => {
 
 	it('renders an undated curated EVENT as a pill, not a broken letter card (REQ-008/016)', () => {
 		render(TimelineView, {
+			canWrite: true,
 			timeline: makeTimelineDTO({
 				undated: [
 					makeEntry({
@@ -125,8 +126,8 @@ describe('TimelineView', () => {
 		// The event renders inside the undated section…
 		expect(document.querySelector('[data-testid="undated-section"]')).not.toBeNull();
 		expect(document.body.textContent).toContain('Auswanderung');
-		// …as an EventPill (its edit affordance), never as a letter card linking
+		// …as an EventPill (its edit affordance, threaded canWrite), never as a
-		// to /documents/undefined with "Unbekannt → Unbekannt".
+		// letter card linking to /documents/undefined with "Unbekannt → Unbekannt".
 		expect(document.querySelector('[data-testid="event-edit"]')).not.toBeNull();
 		expect(document.querySelector('a[href="/documents/undefined"]')).toBeNull();
 		expect(document.body.textContent).not.toContain('Unbekannt');
@@ -276,4 +277,68 @@ describe('TimelineView', () => {
 		);
 		expect(sides).toEqual(['left', 'right', 'left', 'right']);
 	});
+
+	// A curated PERSONAL event reachable through both dispatch paths: the year-band
+	// path (TimelineView → YearBand → EventPill) and the undated bucket
+	// (TimelineView → EventPill). canWrite must thread to both (REQ-009).
+	const curated = (eventId: string, title: string) =>
+		makeEntry({
+			kind: 'EVENT',
+			type: 'PERSONAL',
+			derived: false,
+			eventId,
+			title,
+			senderName: '',
+			receiverName: '',
+			documentId: undefined
+		});
+
+	const bothPaths = () =>
+		makeTimelineDTO({
+			years: [makeYear(1924, [curated('banded', 'Umzug nach Berlin')])],
+			undated: [curated('undated', 'Auswanderung')]
+		});
+
+	it('threads canWrite to a curated event in both a year band and the undated bucket (REQ-009)', () => {
+		render(TimelineView, { canWrite: true, timeline: bothPaths() });
+		const hrefs = Array.from(document.querySelectorAll('[data-testid="event-edit"]')).map((a) =>
+			a.getAttribute('href')
+		);
+		expect(hrefs).toContain('/zeitstrahl/events/banded/edit');
+		expect(hrefs).toContain('/zeitstrahl/events/undated/edit');
+	});
+
+	it('renders no edit links in either path when canWrite is false (REQ-007/009)', () => {
+		render(TimelineView, { canWrite: false, timeline: bothPaths() });
+		expect(document.querySelectorAll('[data-testid="event-edit"]')).toHaveLength(0);
+	});
+
+	it('threads canWrite to a curated HISTORICAL world band in both paths (REQ-006/009)', () => {
+		const world = (eventId: string, title: string) =>
+			makeEntry({
+				kind: 'EVENT',
+				type: 'HISTORICAL',
+				derived: false,
+				eventId,
+				precision: 'YEAR',
+				eventDate: '1929-01-01',
+				eventDateEnd: undefined,
+				title,
+				senderName: '',
+				receiverName: '',
+				documentId: undefined
+			});
+		render(TimelineView, {
+			canWrite: true,
+			timeline: makeTimelineDTO({
+				years: [makeYear(1929, [world('wb', 'Weltwirtschaftskrise')])],
+				undated: [world('wu', 'Unbekanntes Weltereignis')]
+			})
+		});
+		const hrefs = Array.from(document.querySelectorAll('[data-testid="event-edit"]')).map((a) =>
+			a.getAttribute('href')
+		);
+		expect(hrefs).toContain('/zeitstrahl/events/wb/edit');
+		expect(hrefs).toContain('/zeitstrahl/events/wu/edit');
+	});
 });

frontend/src/lib/timeline/WorldBand.svelte

@@ -11,9 +11,11 @@ type TimelineEntryDTO = components['schemas']['TimelineEntryDTO'];
  * (REQ-009). A RANGE carries a visible span pill ("1914–1918") with a Zeitraum
  * aria-label; a RANGE with no end degrades to the start year, no pill (REQ-010).
  * The glyph is a redundant non-color cue with an sr-only label (REQ-018); text
- * uses text-ink-2 to stay AA in both themes (REQ-019).
+ * uses text-ink-2 to stay AA in both themes (REQ-019). A curator (`canWrite`,
+ * gate-closed by default) gets an inline edit pencil for a curated event with an
+ * eventId — #842 REQ-006/007/008; UX gate only, the #781 route guard is the boundary.
  */
-let { entry }: { entry: TimelineEntryDTO } = $props();
+let { entry, canWrite = false }: { entry: TimelineEntryDTO; canWrite?: boolean } = $props();
 
 const config = $derived(getAccentConfig(entry));
 const dateLabel = $derived(timelineDateLabel(entry.eventDate, entry.precision, entry.eventDateEnd));
@@ -24,6 +26,9 @@ const dateText = $derived(showSpan ? null : entry.precision === 'RANGE' ? fromYe
 // Every WorldBand is a HISTORICAL band, so the visible "historisch" register
 // always trails the subtitle as plain text — never a second pill (REQ-009).
 const historical = $derived(m.timeline_layer_historical_suffix());
+// A HISTORICAL event is never derived, so the edit gate is just the curator
+// flag plus a real eventId (#842 REQ-006/008).
+const canEdit = $derived(canWrite && entry.eventId != null);
 </script>
 
 <div class="my-3 border-y border-line bg-canvas px-4 py-2 text-center">
@@ -46,4 +51,14 @@ const historical = $derived(m.timeline_layer_historical_suffix());
 	<!-- Single trailing "· historisch" register, after the title and any
 	     span pill / date — one render site, consistent separator (REQ-009). -->
 	<span class="ml-2 font-sans text-xs text-ink-3">· {historical}</span>
+	{#if canEdit}
+		<a
+			data-testid="event-edit"
+			href="/zeitstrahl/events/{entry.eventId}/edit"
+			class="ml-2 rounded-sm px-1 font-sans text-xs text-ink-3 hover:text-brand-navy focus:outline-none focus-visible:ring-2 focus-visible:ring-brand-navy"
+		>
+			<span aria-hidden="true">✎</span>
+			<span class="sr-only">{m.btn_edit()}</span>
+		</a>
+	{/if}
 </div>

frontend/src/lib/timeline/WorldBand.svelte.spec.ts

@@ -73,4 +73,35 @@ describe('WorldBand', () => {
 		expect(pill?.textContent).not.toContain(m.timeline_layer_historical_suffix());
 		expect(document.body.textContent).toContain(m.timeline_layer_historical_suffix());
 	});
+
+	const HIST_EVENT_ID = '44444444-4444-4444-4444-444444444444';
+
+	it('shows an edit affordance for a curated HISTORICAL event when canWrite is true (REQ-006)', () => {
+		render(WorldBand, { canWrite: true, entry: historical({ eventId: HIST_EVENT_ID }) });
+		const edit = document.querySelector('[data-testid="event-edit"]') as HTMLAnchorElement | null;
+		expect(edit).not.toBeNull();
+		expect(edit?.getAttribute('href')).toBe(`/zeitstrahl/events/${HIST_EVENT_ID}/edit`);
+	});
+
+	it('mirrors the EventPill pencil: aria-hidden ✎ glyph + sr-only Bearbeiten label (REQ-006)', () => {
+		render(WorldBand, { canWrite: true, entry: historical({ eventId: HIST_EVENT_ID }) });
+		const edit = document.querySelector('[data-testid="event-edit"]');
+		expect(edit?.querySelector('[aria-hidden="true"]')?.textContent).toBe('✎');
+		expect(edit?.querySelector('.sr-only')?.textContent).toBe(m.btn_edit());
+	});
+
+	it('renders no edit affordance for a curated HISTORICAL event when canWrite is false (REQ-007)', () => {
+		render(WorldBand, { canWrite: false, entry: historical({ eventId: HIST_EVENT_ID }) });
+		expect(document.querySelector('[data-testid="event-edit"]')).toBeNull();
+	});
+
+	it('renders no edit affordance when the canWrite prop is omitted (gate-closed default) (REQ-007)', () => {
+		render(WorldBand, { entry: historical({ eventId: HIST_EVENT_ID }) });
+		expect(document.querySelector('[data-testid="event-edit"]')).toBeNull();
+	});
+
+	it('shows no edit affordance when eventId is null even with canWrite (REQ-008)', () => {
+		render(WorldBand, { canWrite: true, entry: historical({ eventId: undefined }) });
+		expect(document.querySelector('[data-testid="event-edit"]')).toBeNull();
+	});
 });

frontend/src/lib/timeline/YearBand.svelte

@@ -3,8 +3,14 @@ import EventPill from './EventPill.svelte';
 import WorldBand from './WorldBand.svelte';
 import LetterCard from './LetterCard.svelte';
 import YearLetterStrip from './YearLetterStrip.svelte';
+import LetterBucket from './LetterBucket.svelte';
 import { isDense } from './timelineDensity';
 import { entryKey } from './entryKey';
+import {
+	bucketLetters,
+	type GroupingMode,
+	type LetterBucket as LetterBucketModel
+} from './timelineGrouping';
 import type { components } from '$lib/generated/api';
 
 type TimelineYearDTO = components['schemas']['TimelineYearDTO'];
@@ -15,19 +21,80 @@ type TimelineEntryDTO = components['schemas']['TimelineEntryDTO'];
  * render in DTO order as pills/bands; letters render as individual cards while
  * the band holds ≤ 12 (REQ-011) or collapse to a single density strip above that
  * (REQ-012). Entries are never re-sorted — DTO order is preserved (REQ-003).
+ *
+ * In Ereignis/Thema mode (#827) the event pills/world-bands render identically
+ * (REQ-001); only the loose letters re-bundle into per-year buckets below them
+ * (REQ-002/003/004). Datum mode is the original individual-card / density-strip
+ * path, untouched.
  */
-let { year }: { year: TimelineYearDTO } = $props();
+let {
+	year,
+	canWrite = false,
+	groupingMode = 'date',
+	eventLookup = new Map<string, string>()
+}: {
+	year: TimelineYearDTO;
+	canWrite?: boolean;
+	groupingMode?: GroupingMode;
+	eventLookup?: Map<string, string>;
+} = $props();
 
 type Row =
 	| { t: 'event'; entry: TimelineEntryDTO }
+	| { t: 'eventcard'; entry: TimelineEntryDTO; bucket: LetterBucketModel }
 	| { t: 'letter'; entry: TimelineEntryDTO; side: 'left' | 'right' }
-	| { t: 'strip' };
+	| { t: 'strip' }
+	| { t: 'bucket'; bucket: LetterBucketModel; nested: boolean };
 
 const letters = $derived(year.entries.filter((e) => e.kind === 'LETTER'));
 const dense = $derived(isDense(letters.length));
+const bucketMode = $derived(groupingMode === 'thema' ? 'thema' : 'event');
 
 const rows = $derived.by<Row[]>(() => {
 	const out: Row[] = [];
+
+	// Ereignis: events stay on the axis (REQ-001). A curated event WITH letters in this band
+	// becomes the contained card's header (no separate pill — its title reads once, #827
+	// redesign); a letterless/derived/world event stays a plain pill/band. A cluster whose event
+	// lives in another year band (or was filtered out) renders as a text-header card here, and
+	// the unlinked letters fall to the single "Weitere Briefe" drawer (REQ-003/006/019).
+	if (groupingMode === 'event') {
+		const buckets = bucketLetters(letters, 'event', eventLookup);
+		const sameYearBucket = (id: string | undefined) =>
+			id ? buckets.find((b) => b.kind === 'event' && b.key === `event:${id}`) : undefined;
+		for (const entry of year.entries) {
+			if (entry.kind !== 'EVENT') continue;
+			const bucket = sameYearBucket(entry.eventId);
+			// A curated event with same-year letters becomes the card header (card replaces pill);
+			// otherwise it stays a plain pill/world-band.
+			if (bucket) out.push({ t: 'eventcard', entry, bucket });
+			else out.push({ t: 'event', entry });
+		}
+		// Cross-year clusters (no matching event entry in this band) and the fallback drawer
+		// render after the axis entries, with their own text header.
+		for (const bucket of buckets) {
+			if (
+				bucket.kind === 'fallback' ||
+				!year.entries.some((e) => e.kind === 'EVENT' && `event:${e.eventId}` === bucket.key)
+			) {
+				out.push({ t: 'bucket', bucket, nested: false });
+			}
+		}
+		return out;
+	}
+
+	// Thema: events stay on the axis (REQ-001); loose letters re-bundle into per-year root-tag
+	// buckets below them (REQ-004) — no axis pill exists for a tag, so every bucket keeps a header.
+	if (groupingMode === 'thema') {
+		for (const entry of year.entries) {
+			if (entry.kind === 'EVENT') out.push({ t: 'event', entry });
+		}
+		for (const bucket of bucketLetters(letters, 'thema', eventLookup)) {
+			out.push({ t: 'bucket', bucket, nested: false });
+		}
+		return out;
+	}
+
 	let stripInserted = false;
 	let letterIndex = 0;
 	for (const entry of year.entries) {
@@ -43,6 +110,12 @@ const rows = $derived.by<Row[]>(() => {
 	}
 	return out;
 });
+
+function rowKey(row: Row): string {
+	if (row.t === 'strip') return `strip-${year.year}`;
+	if (row.t === 'bucket') return row.bucket.key;
+	return entryKey(row.entry);
+}
 </script>
 
 <section class="py-2">
@@ -56,18 +129,28 @@ const rows = $derived.by<Row[]>(() => {
 	</h2>
 
 	<div class="mt-3 space-y-3">
-		{#each rows as row (row.t === 'strip' ? `strip-${year.year}` : entryKey(row.entry))}
+		{#each rows as row (rowKey(row))}
 			{#if row.t === 'event'}
 				{#if row.entry.type === 'HISTORICAL'}
-					<WorldBand entry={row.entry} />
+					<WorldBand entry={row.entry} canWrite={canWrite} />
 				{:else}
-					<EventPill entry={row.entry} />
+					<EventPill entry={row.entry} canWrite={canWrite} />
 				{/if}
+			{:else if row.t === 'eventcard'}
+				<LetterBucket
+					bucket={row.bucket}
+					mode="event"
+					year={year.year}
+					event={row.entry}
+					canWrite={canWrite}
+				/>
 			{:else if row.t === 'letter'}
 				<div class="letter-row" data-side={row.side}>
 					<span data-testid="letter-dot" class="letter-dot bg-surface" aria-hidden="true"></span>
 					<LetterCard entry={row.entry} />
 				</div>
+			{:else if row.t === 'bucket'}
+				<LetterBucket bucket={row.bucket} mode={bucketMode} year={year.year} nested={row.nested} />
 			{:else}
 				<YearLetterStrip letters={letters} year={year.year} />
 			{/if}

frontend/src/lib/timeline/YearBand.svelte.spec.ts

@@ -165,3 +165,100 @@ describe('YearBand', () => {
 		}
 	});
 });
+
+describe('YearBand — grouping modes (#827)', () => {
+	it('keeps individual letter cards and no buckets in Datum mode (default)', () => {
+		render(YearBand, { year: makeYear(1915, manyLetters(1915, 3)) });
+		expect(document.querySelector('[data-testid="letter-bucket"]')).toBeNull();
+		expect(document.querySelectorAll('a')).toHaveLength(3);
+	});
+
+	it('clusters loose letters under their linked event in Ereignis mode (REQ-002/003)', () => {
+		const a = makeEntry({ documentId: 'a', linkedEventId: 'e1', eventDate: '1915-03-01' });
+		const b = makeEntry({ documentId: 'b', linkedEventId: 'e1', eventDate: '1915-04-01' });
+		render(YearBand, {
+			year: makeYear(1915, [a, b]),
+			groupingMode: 'event',
+			eventLookup: new Map([['e1', 'Briefe von der Front']])
+		});
+		expect(document.querySelectorAll('[data-testid="letter-bucket"]')).toHaveLength(1);
+		expect(document.body.textContent).toContain('Briefe von der Front');
+		// no alternating individual letter rows in grouped mode
+		expect(document.querySelector('.letter-row')).toBeNull();
+	});
+
+	it('still renders the event world-band in Ereignis mode (REQ-001)', () => {
+		const band = makeEntry({
+			kind: 'EVENT',
+			type: 'HISTORICAL',
+			precision: 'RANGE',
+			eventDate: '1914-01-01',
+			eventDateEnd: '1918-12-31',
+			title: 'Erster Weltkrieg',
+			senderName: '',
+			receiverName: '',
+			documentId: undefined
+		});
+		const letter = makeEntry({ documentId: 'a', linkedEventId: 'e1', eventDate: '1914-05-01' });
+		render(YearBand, {
+			year: makeYear(1914, [band, letter]),
+			groupingMode: 'event',
+			eventLookup: new Map([['e1', 'Front']])
+		});
+		expect(document.querySelector('[data-testid="world-range"]')).not.toBeNull();
+		expect(document.querySelector('[data-testid="letter-bucket"]')).not.toBeNull();
+	});
+
+	it('buckets loose letters under their root tag in Thema mode (REQ-004)', () => {
+		const a = makeEntry({
+			documentId: 'a',
+			rootTagId: 't1',
+			rootTagName: 'Krieg',
+			rootTagColor: 'sienna',
+			eventDate: '1915-03-01'
+		});
+		render(YearBand, { year: makeYear(1915, [a]), groupingMode: 'thema', eventLookup: new Map() });
+		const chip = document.querySelector('[data-testid="bucket-header-chip"]');
+		expect(chip?.textContent).toContain('Krieg');
+	});
+
+	it('renders a same-year curated event as one card header, with no separate pill and no duplicate title (#827)', () => {
+		const pill = makeEntry({
+			kind: 'EVENT',
+			type: 'PERSONAL',
+			derived: false,
+			eventId: 'e1',
+			title: 'Ein gewaltiger Stadtbrand',
+			eventDate: '1916-07-06',
+			senderName: '',
+			receiverName: '',
+			documentId: undefined
+		});
+		const letter = makeEntry({ documentId: 'a', linkedEventId: 'e1', eventDate: '1916-07-06' });
+		render(YearBand, {
+			year: makeYear(1916, [pill, letter]),
+			groupingMode: 'event',
+			eventLookup: new Map([['e1', 'Ein gewaltiger Stadtbrand']]),
+			canWrite: true
+		});
+		// the title appears exactly once — in the card header, not also as a separate pill
+		const occurrences =
+			(document.body.textContent ?? '').split('Ein gewaltiger Stadtbrand').length - 1;
+		expect(occurrences).toBe(1);
+		// the event renders as the card header, with its letter clustered inside
+		expect(document.querySelector('[data-testid="bucket-event-header"]')).not.toBeNull();
+		expect(document.querySelector('a.lcard.ev')).not.toBeNull();
+	});
+
+	it('keeps a header on an event cluster whose pill is in another year (#827)', () => {
+		// the letter links to e1, but e1's pill lives in a different band — so the cluster
+		// keeps its own header here (no pill nearby to duplicate).
+		const letter = makeEntry({ documentId: 'a', linkedEventId: 'e1', eventDate: '1917-02-01' });
+		render(YearBand, {
+			year: makeYear(1917, [letter]),
+			groupingMode: 'event',
+			eventLookup: new Map([['e1', 'Briefe von der Front']])
+		});
+		expect(document.body.textContent).toContain('Briefe von der Front');
+	});
+});

frontend/src/lib/timeline/grouping-event-layer-identity.svelte.spec.ts

@@ -0,0 +1,98 @@
+import { describe, it, expect, afterEach } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import TimelineView from './TimelineView.svelte';
+import { makeEntry, makeYear, makeTimelineDTO } from './test-factories';
+import type { GroupingMode } from './timelineGrouping';
+
+afterEach(() => cleanup());
+
+const worldBand = (title: string) =>
+	makeEntry({
+		kind: 'EVENT',
+		type: 'HISTORICAL',
+		derived: false,
+		precision: 'RANGE',
+		eventDate: '1914-01-01',
+		eventDateEnd: '1918-12-31',
+		eventId: 'h1',
+		title,
+		senderName: '',
+		receiverName: '',
+		documentId: undefined
+	});
+
+const eventPill = (title: string) =>
+	makeEntry({
+		kind: 'EVENT',
+		type: 'PERSONAL',
+		derived: false,
+		eventId: 'p1',
+		title,
+		senderName: '',
+		receiverName: '',
+		documentId: undefined
+	});
+
+// A signature of the axis-fixed event layer: the curated/world-band titles, the world-range
+// marker count, and the event-pill count — everything REQ-001 requires to stay constant when
+// only the loose letters re-bundle. (No pixel-diff harness in the repo; this is the structural
+// equivalent — the event-layer DOM is byte-for-byte built from the same entries in every mode.)
+function eventLayerSignature(): string {
+	const body = document.body.textContent ?? '';
+	return JSON.stringify({
+		weltkrieg: body.includes('Erster Weltkrieg'),
+		hochzeit: body.includes('Hochzeit'),
+		worldRange: document.querySelectorAll('[data-testid="world-range"]').length
+	});
+}
+
+// Brief A links to the curated event p1 (Hochzeit), not the world band — so the world band
+// stays letterless and renders as a plain band in every mode (REQ-001). Under the #827 redesign
+// a curated event WITH letters becomes its cluster card's header, so the signature tracks the
+// stable layer: the letterless world band's marker count and the two titles, which all survive
+// regardless of whether Hochzeit renders as a pill (Datum) or a card header (grouped).
+const mixed = () =>
+	makeTimelineDTO({
+		years: [
+			makeYear(1915, [
+				worldBand('Erster Weltkrieg'),
+				eventPill('Hochzeit'),
+				makeEntry({ documentId: 'a', title: 'Brief A', linkedEventId: 'p1' }),
+				makeEntry({
+					documentId: 'b',
+					title: 'Brief B',
+					rootTagId: 't1',
+					rootTagName: 'Krieg',
+					rootTagColor: 'sienna'
+				})
+			])
+		]
+	});
+
+function signatureFor(mode: GroupingMode): string {
+	render(TimelineView, { timeline: mixed(), groupingMode: mode });
+	const sig = eventLayerSignature();
+	cleanup();
+	return sig;
+}
+
+describe('TimelineView event layer (REQ-001)', () => {
+	it('renders the event pills and world-bands identically across all three grouping modes', () => {
+		const dateSig = signatureFor('date');
+		const eventSig = signatureFor('event');
+		const themaSig = signatureFor('thema');
+
+		expect(eventSig).toBe(dateSig);
+		expect(themaSig).toBe(dateSig);
+		// sanity: the world-band actually rendered, so the assertion is not vacuously equal on ""
+		expect(dateSig).toContain('"worldRange":1');
+	});
+
+	it('regroups only the loose letters — buckets appear off Datum, not in it', () => {
+		render(TimelineView, { timeline: mixed(), groupingMode: 'date' });
+		expect(document.querySelector('[data-testid="letter-bucket"]')).toBeNull();
+		cleanup();
+		render(TimelineView, { timeline: mixed(), groupingMode: 'event' });
+		expect(document.querySelector('[data-testid="letter-bucket"]')).not.toBeNull();
+	});
+});

frontend/src/lib/timeline/timeline-no-raw-html.spec.ts

@@ -0,0 +1,23 @@
+import { describe, it, expect } from 'vitest';
+import { readdirSync, readFileSync } from 'node:fs';
+import { fileURLToPath } from 'node:url';
+import { dirname, join } from 'node:path';
+
+const timelineDir = dirname(fileURLToPath(import.meta.url));
+
+/**
+ * REQ-009 / CWE-79: the regroup touches every component under lib/timeline (the reused TagChip,
+ * the .lcard.ev card, and the new tinted bucket-header chip). Curator/import-derived text must
+ * always render through Svelte's default `{...}` escaping — never `{@html}`. This grep gate fails
+ * loudly the moment any timeline component reaches for the raw-HTML directive.
+ */
+describe('lib/timeline never uses {@html} (REQ-009)', () => {
+	it('no timeline component contains the raw-HTML directive', () => {
+		const components = readdirSync(timelineDir).filter((file) => file.endsWith('.svelte'));
+		expect(components.length).toBeGreaterThan(0);
+		const offenders = components.filter((file) =>
+			readFileSync(join(timelineDir, file), 'utf8').includes('{@html')
+		);
+		expect(offenders).toEqual([]);
+	});
+});

frontend/src/lib/timeline/timelineFilter.spec.ts

@@ -0,0 +1,151 @@
+import { describe, it, expect } from 'vitest';
+import {
+	isDefaultState,
+	hiddenLayerCount,
+	filterTimeline,
+	ALL_LAYERS_ON,
+	type TimelineLayerFilters
+} from './timelineFilter';
+import { makeEntry, makeYear, makeTimelineDTO } from './test-factories';
+
+// Entry factories pinned to the three layers the filter discriminates (#780).
+const letter = (overrides = {}) => makeEntry({ kind: 'LETTER', ...overrides });
+
+const curatedPersonal = (overrides = {}) =>
+	makeEntry({
+		kind: 'EVENT',
+		type: 'PERSONAL',
+		derived: false,
+		documentId: undefined,
+		title: 'Umzug nach Berlin',
+		senderName: '',
+		receiverName: '',
+		...overrides
+	});
+
+// Derived life-events carry type=PERSONAL (issue #776 REQ-009) — they belong to
+// the Personal layer, not a fourth one.
+const derivedLifeEvent = (overrides = {}) =>
+	makeEntry({
+		kind: 'EVENT',
+		type: 'PERSONAL',
+		derived: true,
+		derivedType: 'BIRTH',
+		documentId: undefined,
+		title: 'Geburt',
+		senderName: '',
+		receiverName: '',
+		...overrides
+	});
+
+const historical = (overrides = {}) =>
+	makeEntry({
+		kind: 'EVENT',
+		type: 'HISTORICAL',
+		derived: false,
+		documentId: undefined,
+		title: 'Erster Weltkrieg',
+		senderName: '',
+		receiverName: '',
+		...overrides
+	});
+
+const off = (overrides: Partial<TimelineLayerFilters>): TimelineLayerFilters => ({
+	...ALL_LAYERS_ON,
+	...overrides
+});
+
+describe('isDefaultState (REQ-007)', () => {
+	it('is true when all three layers are on', () => {
+		expect(isDefaultState(ALL_LAYERS_ON)).toBe(true);
+	});
+
+	it('is false when any single layer is off', () => {
+		expect(isDefaultState(off({ personalOn: false }))).toBe(false);
+		expect(isDefaultState(off({ historicalOn: false }))).toBe(false);
+		expect(isDefaultState(off({ lettersOn: false }))).toBe(false);
+	});
+});
+
+describe('hiddenLayerCount (REQ-007)', () => {
+	it('is 0 in the default all-on state', () => {
+		expect(hiddenLayerCount(ALL_LAYERS_ON)).toBe(0);
+	});
+
+	it('counts each layer that is off', () => {
+		expect(hiddenLayerCount(off({ lettersOn: false }))).toBe(1);
+		expect(hiddenLayerCount(off({ personalOn: false, historicalOn: false }))).toBe(2);
+		expect(hiddenLayerCount({ personalOn: false, historicalOn: false, lettersOn: false })).toBe(3);
+	});
+});
+
+describe('filterTimeline', () => {
+	it('returns every entry unchanged in the default all-on state', () => {
+		const dto = makeTimelineDTO({
+			years: [makeYear(1915, [letter(), historical(), curatedPersonal()])],
+			undated: [letter({ documentId: 'u1' })]
+		});
+		const result = filterTimeline(dto, ALL_LAYERS_ON);
+		expect(result.years[0].entries).toHaveLength(3);
+		expect(result.undated).toHaveLength(1);
+	});
+
+	it('hides LETTER entries when lettersOn is false, keeping events (REQ-005)', () => {
+		const dto = makeTimelineDTO({
+			years: [makeYear(1915, [letter(), historical(), curatedPersonal()])],
+			undated: [letter({ documentId: 'u1' })]
+		});
+		const result = filterTimeline(dto, off({ lettersOn: false }));
+		expect(result.years[0].entries.every((e) => e.kind !== 'LETTER')).toBe(true);
+		expect(result.years[0].entries).toHaveLength(2);
+		expect(result.undated).toHaveLength(0);
+	});
+
+	it('hides HISTORICAL events when historicalOn is false, keeping personal + letters (REQ-004)', () => {
+		const dto = makeTimelineDTO({
+			years: [makeYear(1915, [letter(), historical(), curatedPersonal(), derivedLifeEvent()])]
+		});
+		const result = filterTimeline(dto, off({ historicalOn: false }));
+		const kept = result.years[0].entries;
+		expect(kept.some((e) => e.kind === 'EVENT' && e.type === 'HISTORICAL')).toBe(false);
+		expect(kept.some((e) => e.kind === 'LETTER')).toBe(true);
+		expect(kept.some((e) => e.kind === 'EVENT' && e.type === 'PERSONAL')).toBe(true);
+		expect(kept).toHaveLength(3);
+	});
+
+	it('hides personal events — curated and derived — when personalOn is false (REQ-003)', () => {
+		const dto = makeTimelineDTO({
+			years: [makeYear(1915, [letter(), historical(), curatedPersonal(), derivedLifeEvent()])]
+		});
+		const result = filterTimeline(dto, off({ personalOn: false }));
+		const kept = result.years[0].entries;
+		// neither the curated PERSONAL event nor the derived life-event survives
+		expect(kept.some((e) => e.kind === 'EVENT' && e.type === 'PERSONAL')).toBe(false);
+		expect(kept.some((e) => e.derived)).toBe(false);
+		// historical events and letters are untouched
+		expect(kept.some((e) => e.kind === 'EVENT' && e.type === 'HISTORICAL')).toBe(true);
+		expect(kept.some((e) => e.kind === 'LETTER')).toBe(true);
+		expect(kept).toHaveLength(2);
+	});
+
+	it('drops year bands that become empty and filters the undated bucket (REQ-006)', () => {
+		const dto = makeTimelineDTO({
+			years: [
+				makeYear(1915, [letter()]), // becomes empty when letters are hidden
+				makeYear(1918, [historical()]) // survives
+			],
+			undated: [letter({ documentId: 'u1' }), historical({ documentId: undefined })]
+		});
+		const result = filterTimeline(dto, off({ lettersOn: false }));
+		expect(result.years).toHaveLength(1);
+		expect(result.years[0].year).toBe(1918);
+		expect(result.undated.every((e) => e.kind !== 'LETTER')).toBe(true);
+		expect(result.undated).toHaveLength(1);
+	});
+
+	it('does not mutate the input timeline', () => {
+		const dto = makeTimelineDTO({ years: [makeYear(1915, [letter(), historical()])] });
+		filterTimeline(dto, off({ lettersOn: false }));
+		expect(dto.years[0].entries).toHaveLength(2);
+	});
+});

frontend/src/lib/timeline/timelineFilter.ts

@@ -0,0 +1,63 @@
+import type { components } from '$lib/generated/api';
+
+type TimelineDTO = components['schemas']['TimelineDTO'];
+type TimelineEntryDTO = components['schemas']['TimelineEntryDTO'];
+
+/**
+ * The three visibility layers a reader can toggle on the global `/zeitstrahl`
+ * (#780). Purely a presentation concern — the whole timeline is loaded once by
+ * #779; these toggles derive a client-side filtered view of it.
+ */
+export interface TimelineLayerFilters {
+	/** Personal events — curated `PERSONAL` events and derived life-events. */
+	personalOn: boolean;
+	/** Historical events (`type === 'HISTORICAL'`). */
+	historicalOn: boolean;
+	/** Letters (`kind === 'LETTER'`). */
+	lettersOn: boolean;
+}
+
+/** The default view: every layer visible. */
+export const ALL_LAYERS_ON: TimelineLayerFilters = {
+	personalOn: true,
+	historicalOn: true,
+	lettersOn: true
+};
+
+/** True when no layer is hidden — the default, all-on state (REQ-007). */
+export function isDefaultState(filters: TimelineLayerFilters): boolean {
+	return filters.personalOn && filters.historicalOn && filters.lettersOn;
+}
+
+/** How many layers are currently hidden — the "N active" trigger count (REQ-007). */
+export function hiddenLayerCount(filters: TimelineLayerFilters): number {
+	return (
+		(filters.personalOn ? 0 : 1) + (filters.historicalOn ? 0 : 1) + (filters.lettersOn ? 0 : 1)
+	);
+}
+
+/**
+ * Decides whether one entry survives the active layer toggles. A letter rides
+ * the Letters layer; a historical event the Historical layer; everything else
+ * (curated `PERSONAL` events and derived life-events, which also carry
+ * `type === 'PERSONAL'`) the Personal layer.
+ */
+function isVisible(entry: TimelineEntryDTO, filters: TimelineLayerFilters): boolean {
+	if (entry.kind === 'LETTER') return filters.lettersOn;
+	if (entry.type === 'HISTORICAL') return filters.historicalOn;
+	return filters.personalOn;
+}
+
+/**
+ * Derives a client-side filtered copy of the timeline (REQ-003/004/005/006).
+ * Year bands left empty by the active toggles are dropped so `TimelineView`
+ * never renders a hollow band, and the undated bucket is filtered the same way.
+ * Pure — the input DTO is never mutated.
+ */
+export function filterTimeline(timeline: TimelineDTO, filters: TimelineLayerFilters): TimelineDTO {
+	const years = timeline.years
+		.map((band) => ({ ...band, entries: band.entries.filter((e) => isVisible(e, filters)) }))
+		.filter((band) => band.entries.length > 0);
+	const undated = timeline.undated.filter((e) => isVisible(e, filters));
+	return { years, undated };
+}

frontend/src/lib/timeline/timelineFilterBoundary.spec.ts

@@ -0,0 +1,37 @@
+import { describe, it, expect } from 'vitest';
+import { readFileSync } from 'node:fs';
+import { fileURLToPath } from 'node:url';
+
+// REQ-001/002: the layer filter is presentation-only and fully client-side. It
+// must never navigate or fetch — the route derives the filtered view from
+// already-loaded data. This static guard mirrors the project's existing
+// grep-gates (e.g. the no-`{@html}` checks) and fails the build if a future
+// edit reintroduces navigation or a network call into either file.
+const read = (relative: string) =>
+	readFileSync(fileURLToPath(new URL(relative, import.meta.url)), 'utf8');
+
+const FILES = {
+	'TimelineFilters.svelte': read('./TimelineFilters.svelte'),
+	'/zeitstrahl/+page.svelte': read('../../routes/zeitstrahl/+page.svelte')
+};
+
+const FORBIDDEN: { label: string; pattern: RegExp }[] = [
+	{ label: 'goto(', pattern: /\bgoto\s*\(/ },
+	{ label: 'url.searchParams', pattern: /url\.searchParams/ },
+	{ label: 'api.GET', pattern: /\bapi\.GET\b/ },
+	{ label: 'fetch(', pattern: /\bfetch\s*\(/ }
+];
+
+describe('layer-filter boundary (REQ-001/002)', () => {
+	for (const [name, source] of Object.entries(FILES)) {
+		it(`${name} was found and is non-empty`, () => {
+			expect(source.length).toBeGreaterThan(0);
+		});
+
+		for (const { label, pattern } of FORBIDDEN) {
+			it(`${name} contains no ${label}`, () => {
+				expect(pattern.test(source), `${name} must not use ${label}`).toBe(false);
+			});
+		}
+	}
+});

frontend/src/lib/timeline/timelineGrouping.spec.ts

@@ -0,0 +1,157 @@
+import { describe, it, expect } from 'vitest';
+import { buildEventLookup, bucketLetters, hasLooseLetters } from './timelineGrouping';
+import { makeEntry, makeYear, makeTimelineDTO } from './test-factories';
+
+// Entry factories pinned to the shapes the grouping transform discriminates (#827).
+const letter = (overrides = {}) => makeEntry({ kind: 'LETTER', ...overrides });
+
+const curatedEvent = (id: string, title: string, overrides = {}) =>
+	makeEntry({
+		kind: 'EVENT',
+		type: 'PERSONAL',
+		derived: false,
+		documentId: undefined,
+		eventId: id,
+		title,
+		senderName: '',
+		receiverName: '',
+		...overrides
+	});
+
+describe('buildEventLookup (REQ-019)', () => {
+	it('collects curated events (eventId set) from year bands and the undated bucket', () => {
+		const dto = makeTimelineDTO({
+			years: [makeYear(1915, [curatedEvent('e1', 'Briefe von der Front'), letter()])],
+			undated: [curatedEvent('e2', 'Unbekanntes Ereignis')]
+		});
+		const lookup = buildEventLookup(dto);
+		expect(lookup.get('e1')).toBe('Briefe von der Front');
+		expect(lookup.get('e2')).toBe('Unbekanntes Ereignis');
+		expect(lookup.size).toBe(2);
+	});
+
+	it('ignores letters and derived life-events (no eventId)', () => {
+		const dto = makeTimelineDTO({
+			years: [
+				makeYear(1915, [
+					letter({ linkedEventId: 'e1' }),
+					makeEntry({ kind: 'EVENT', type: 'PERSONAL', derived: true, eventId: undefined })
+				])
+			]
+		});
+		expect(buildEventLookup(dto).size).toBe(0);
+	});
+});
+
+describe('hasLooseLetters (REQ-018)', () => {
+	it('is true when a year band or the undated bucket holds a letter', () => {
+		expect(hasLooseLetters(makeTimelineDTO({ years: [makeYear(1915, [letter()])] }))).toBe(true);
+		expect(hasLooseLetters(makeTimelineDTO({ undated: [letter({ documentId: 'u1' })] }))).toBe(
+			true
+		);
+	});
+
+	it('is false when only events remain', () => {
+		const dto = makeTimelineDTO({ years: [makeYear(1915, [curatedEvent('e1', 'Ereignis')])] });
+		expect(hasLooseLetters(dto)).toBe(false);
+	});
+});
+
+describe('bucketLetters — Ereignis mode (REQ-003/006/019)', () => {
+	const lookup = new Map([
+		['e1', 'Briefe von der Front'],
+		['e2', 'Weihnachten 1915']
+	]);
+
+	it('clusters letters under the curated event named by linkedEventId, with matching counts', () => {
+		const letters = [
+			letter({ documentId: 'a', linkedEventId: 'e1' }),
+			letter({ documentId: 'b', linkedEventId: 'e1' }),
+			letter({ documentId: 'c', linkedEventId: 'e2' })
+		];
+		const buckets = bucketLetters(letters, 'event', lookup);
+		const front = buckets.find((b) => b.title === 'Briefe von der Front');
+		expect(front?.kind).toBe('event');
+		expect(front?.letters).toHaveLength(2);
+		expect(buckets.find((b) => b.title === 'Weihnachten 1915')?.letters).toHaveLength(1);
+	});
+
+	it('drops a letter with no linkedEventId into the fallback bucket (REQ-006)', () => {
+		const letters = [letter({ documentId: 'a', linkedEventId: undefined })];
+		const buckets = bucketLetters(letters, 'event', lookup);
+		expect(buckets).toHaveLength(1);
+		expect(buckets[0].kind).toBe('fallback');
+		expect(buckets[0].letters).toHaveLength(1);
+	});
+
+	it('drops a letter whose linked event is absent from the lookup into fallback (REQ-019)', () => {
+		// e9 is not in the filtered view (its layer was toggled off) → no cluster.
+		const letters = [letter({ documentId: 'a', linkedEventId: 'e9' })];
+		const buckets = bucketLetters(letters, 'event', lookup);
+		expect(buckets).toHaveLength(1);
+		expect(buckets[0].kind).toBe('fallback');
+	});
+
+	it('keeps the fallback bucket last', () => {
+		const letters = [
+			letter({ documentId: 'a', linkedEventId: undefined }),
+			letter({ documentId: 'b', linkedEventId: 'e1' })
+		];
+		const buckets = bucketLetters(letters, 'event', lookup);
+		expect(buckets[buckets.length - 1].kind).toBe('fallback');
+	});
+});
+
+describe('bucketLetters — Thema mode (REQ-004/007/008)', () => {
+	const noEvents = new Map<string, string>();
+
+	it('buckets letters under their primary root tag with name and colour', () => {
+		const letters = [
+			letter({ documentId: 'a', rootTagId: 't1', rootTagName: 'Krieg', rootTagColor: 'sienna' }),
+			letter({ documentId: 'b', rootTagId: 't1', rootTagName: 'Krieg', rootTagColor: 'sienna' }),
+			letter({
+				documentId: 'c',
+				rootTagId: 't2',
+				rootTagName: 'Weihnachten',
+				rootTagColor: 'amber'
+			})
+		];
+		const buckets = bucketLetters(letters, 'thema', noEvents);
+		const krieg = buckets.find((b) => b.title === 'Krieg');
+		expect(krieg?.kind).toBe('tag');
+		expect(krieg?.color).toBe('sienna');
+		expect(krieg?.letters).toHaveLength(2);
+		expect(buckets.find((b) => b.title === 'Weihnachten')?.color).toBe('amber');
+	});
+
+	it('drops an untagged letter into the "Ohne Thema" fallback bucket (REQ-007)', () => {
+		const letters = [letter({ documentId: 'a', rootTagId: undefined })];
+		const buckets = bucketLetters(letters, 'thema', noEvents);
+		expect(buckets).toHaveLength(1);
+		expect(buckets[0].kind).toBe('fallback');
+		expect(buckets[0].color).toBeNull();
+	});
+
+	it('places a letter in exactly one bucket (REQ-008)', () => {
+		const letters = [
+			letter({ documentId: 'a', rootTagId: 't1', rootTagName: 'Krieg', rootTagColor: 'sienna' })
+		];
+		const buckets = bucketLetters(letters, 'thema', noEvents);
+		const occurrences = buckets.flatMap((b) => b.letters).filter((l) => l.documentId === 'a');
+		expect(occurrences).toHaveLength(1);
+	});
+
+	it('carries a null colour through for a colourless root tag', () => {
+		const letters = [
+			letter({
+				documentId: 'a',
+				rootTagId: 't3',
+				rootTagName: 'Allgemein',
+				rootTagColor: undefined
+			})
+		];
+		const buckets = bucketLetters(letters, 'thema', noEvents);
+		expect(buckets[0].kind).toBe('tag');
+		expect(buckets[0].color).toBeNull();
+	});
+});

frontend/src/lib/timeline/timelineGrouping.ts

@@ -0,0 +1,152 @@
+import type { components } from '$lib/generated/api';
+
+type TimelineDTO = components['schemas']['TimelineDTO'];
+type TimelineEntryDTO = components['schemas']['TimelineEntryDTO'];
+
+/**
+ * The three ways a reader can bundle the loose letters on `/zeitstrahl` (#827). The
+ * axis-fixed layers (life-events, event pills, world-bands) are identical in every mode
+ * — only loose-letter bundling changes. Grouping runs over the *already layer-filtered*
+ * timeline (#780): filter-then-group.
+ */
+export type GroupingMode = 'date' | 'event' | 'thema';
+
+/** The default mode — chronological, as #779 shipped. */
+export const DEFAULT_GROUPING: GroupingMode = 'date';
+
+/** Letters shown before a cluster needs a "show more" toggle (#827 redesign). */
+export const CLUSTER_PREVIEW = 5;
+
+/** The `--c-tag-*` colour-name tokens (sage/sienna/…); shared by the chip and the rail. */
+const TAG_COLOR_TOKENS = new Set([
+	'sage',
+	'sienna',
+	'amber',
+	'slate',
+	'violet',
+	'rose',
+	'cobalt',
+	'moss',
+	'sand',
+	'coral'
+]);
+
+/**
+ * Maps a root-tag colour-name token to its CSS variable reference, or `null` for an absent
+ * or unknown token (so a colourless/unrecognised tag falls back to a neutral rail, never a
+ * broken `var(--c-tag-undefined)`).
+ */
+export function tagColorVar(token: string | null | undefined): string | null {
+	return token && TAG_COLOR_TOKENS.has(token) ? `var(--c-tag-${token})` : null;
+}
+
+/**
+ * One bundle of loose letters under a single header, within a year (Ereignis/Thema modes).
+ * `kind` decides the header: a curated-event title, a tinted root-tag chip, or the localized
+ * fallback ("Weitere Briefe" / "Ohne Thema") the view supplies for `kind === 'fallback'`.
+ */
+export interface LetterBucket {
+	/** Stable `{#each}` key, unique within a year's bucket list. */
+	key: string;
+	kind: 'event' | 'tag' | 'fallback';
+	/** Header label for `event`/`tag` buckets; absent for `fallback` (view supplies a localized label). */
+	title?: string;
+	/** Root-tag colour token for a `tag` bucket; `null` for `event`/`fallback` (neutral). */
+	color: string | null;
+	letters: TimelineEntryDTO[];
+}
+
+/**
+ * Maps each curated event present in the (already-filtered) timeline to its title. These are the
+ * only events a letter may cluster under — a letter whose `linkedEventId` is absent here links to
+ * an event the layer filter removed, so it falls back to "Weitere Briefe" (filter-then-group,
+ * REQ-019). Curated events carry an `eventId`; derived life-events and letters do not.
+ */
+export function buildEventLookup(timeline: TimelineDTO): Map<string, string> {
+	const lookup = new Map<string, string>();
+	const collect = (entries: TimelineEntryDTO[]) => {
+		for (const entry of entries) {
+			if (entry.kind === 'EVENT' && entry.eventId) lookup.set(entry.eventId, entry.title ?? '');
+		}
+	};
+	for (const band of timeline.years) collect(band.entries);
+	collect(timeline.undated);
+	return lookup;
+}
+
+/**
+ * True when the timeline still holds at least one loose letter. Drives the grouping control's
+ * enabled state: with the Letters layer filtered off there is nothing to regroup (REQ-018).
+ */
+export function hasLooseLetters(timeline: TimelineDTO): boolean {
+	const holdsLetter = (entries: TimelineEntryDTO[]) => entries.some((e) => e.kind === 'LETTER');
+	return timeline.years.some((band) => holdsLetter(band.entries)) || holdsLetter(timeline.undated);
+}
+
+/**
+ * Buckets one year's loose letters for Ereignis/Thema mode. The caller passes only that year's
+ * `LETTER` entries; events stay on the axis untouched (REQ-001). Buckets keep first-seen order and
+ * the fallback bucket, if any, always sorts last.
+ *
+ * - `event`: cluster under `linkedEventId` when it is set AND survives in `eventLookup`; otherwise
+ *   the fallback "Weitere Briefe" bucket (REQ-003/006/019).
+ * - `thema`: bucket under `rootTagId` (header = `rootTagName`, tint = `rootTagColor`); an untagged
+ *   letter goes to the fallback "Ohne Thema" bucket (REQ-004/007). A letter carries exactly one
+ *   `rootTagId`, so it lands in exactly one bucket (REQ-008).
+ */
+export function bucketLetters(
+	letters: TimelineEntryDTO[],
+	mode: Exclude<GroupingMode, 'date'>,
+	eventLookup: Map<string, string>
+): LetterBucket[] {
+	const byKey = new Map<string, LetterBucket>();
+	let fallback: LetterBucket | null = null;
+
+	const fallbackBucket = (): LetterBucket => {
+		if (!fallback) fallback = { key: '__fallback__', kind: 'fallback', color: null, letters: [] };
+		return fallback;
+	};
+
+	const namedBucket = (id: string, build: () => LetterBucket): LetterBucket => {
+		let bucket = byKey.get(id);
+		if (!bucket) {
+			bucket = build();
+			byKey.set(id, bucket);
+		}
+		return bucket;
+	};
+
+	for (const letter of letters) {
+		if (mode === 'event') {
+			const id = letter.linkedEventId;
+			if (id && eventLookup.has(id)) {
+				namedBucket(id, () => ({
+					key: `event:${id}`,
+					kind: 'event',
+					title: eventLookup.get(id),
+					color: null,
+					letters: []
+				})).letters.push(letter);
+			} else {
+				fallbackBucket().letters.push(letter);
+			}
+		} else {
+			const id = letter.rootTagId;
+			if (id) {
+				namedBucket(id, () => ({
+					key: `tag:${id}`,
+					kind: 'tag',
+					title: letter.rootTagName ?? '',
+					color: letter.rootTagColor ?? null,
+					letters: []
+				})).letters.push(letter);
+			} else {
+				fallbackBucket().letters.push(letter);
+			}
+		}
+	}
+
+	const buckets = [...byKey.values()];
+	if (fallback) buckets.push(fallback);
+	return buckets;
+}

frontend/src/routes/persons/[id]/PersonCard.svelte

@@ -128,7 +128,8 @@ const deathText = $derived(formatLifeDate(person.deathDate, person.deathDatePrec
 			</div>
 		{/if}
 
-		<!-- Edit button — full width, outlined -->
+		<!-- Curator actions — full width, outlined. Both links are gated to
+		     WRITE_ALL; the gate is UX only (the #781 route guard is the boundary). -->
 		{#if canWrite}
 			<a
 				href="/persons/{person.id}/edit"
@@ -142,6 +143,15 @@ const deathText = $derived(formatLifeDate(person.deathDate, person.deathDatePrec
 				/>
 				{m.btn_edit()}
 			</a>
+			<!-- Opens #781's create form pre-seeded with this person; on save it
+			     returns to /persons/{id} (originPersonId). #842 REQ-003/010. -->
+			<a
+				data-testid="person-add-event"
+				href="/zeitstrahl/events/new?personId={person.id}"
+				class="mt-2 flex min-h-[44px] w-full items-center justify-center rounded border border-line px-3 py-2 font-sans text-xs font-bold tracking-widest text-ink-2 uppercase transition-colors hover:border-primary hover:text-ink"
+			>
+				{m.person_add_event()}
+			</a>
 		{/if}
 	</div>
 </div>

frontend/src/routes/persons/[id]/PersonCard.svelte.spec.ts

@@ -0,0 +1,32 @@
+import { describe, it, expect, afterEach } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import PersonCard from './PersonCard.svelte';
+
+afterEach(() => cleanup());
+
+const PERSON_ID = '55555555-5555-5555-5555-555555555555';
+
+const makePerson = (overrides = {}) => ({
+	id: PERSON_ID,
+	firstName: 'Karl',
+	lastName: 'Raddatz',
+	displayName: 'Karl Raddatz',
+	personType: 'PERSON',
+	...overrides
+});
+
+describe('PersonCard add-event affordance (#842)', () => {
+	it('shows an add-event link pre-seeded with the person to a curator (REQ-003)', () => {
+		render(PersonCard, { person: makePerson(), canWrite: true });
+		const add = document.querySelector(
+			'[data-testid="person-add-event"]'
+		) as HTMLAnchorElement | null;
+		expect(add).not.toBeNull();
+		expect(add?.getAttribute('href')).toBe(`/zeitstrahl/events/new?personId=${PERSON_ID}`);
+	});
+
+	it('renders no add-event link to a reader (REQ-004)', () => {
+		render(PersonCard, { person: makePerson(), canWrite: false });
+		expect(document.querySelector('[data-testid="person-add-event"]')).toBeNull();
+	});
+});

frontend/src/routes/persons/[id]/PersonRelationshipsCard.svelte

@@ -1,6 +1,7 @@
 <script lang="ts">
 import { m } from '$lib/paraglide/messages.js';
 import { chipLabel, otherName, inferredRelationshipLabel } from '$lib/person/relationshipLabels';
+import { formatRelationshipDateRange } from '$lib/person/relationshipDates';
 import type { components } from '$lib/generated/api';
 
 type RelationshipDTO = components['schemas']['RelationshipDTO'];
@@ -35,7 +36,14 @@ function otherId(rel: RelationshipDTO): string {
 		{#if relationships.length > 0}
 			<ul class="mb-4 space-y-2">
 				{#each relationships as rel (rel.id)}
-					<li class="flex items-center gap-2">
+					{@const dateRange = formatRelationshipDateRange(
+						rel.fromDate,
+						rel.fromDatePrecision,
+						rel.toDate,
+						rel.toDatePrecision
+					)}
+					<li class="flex flex-col gap-0.5">
+						<div class="flex items-center gap-2">
 							<span
 								class="inline-flex shrink-0 items-center rounded-full border border-accent/40 bg-accent/15 px-2 py-0.5 font-sans text-xs font-bold tracking-widest text-ink uppercase"
 							>
@@ -47,6 +55,18 @@ function otherId(rel: RelationshipDTO): string {
 							>
 								{otherName(rel, personId)}
 							</a>
+							{#if dateRange}
+								<span
+									class="shrink-0 font-sans text-xs text-ink-3"
+									data-testid="relationship-date-range">{dateRange}</span
+								>
+							{/if}
+						</div>
+						{#if rel.notes}
+							<p class="pl-1 font-serif text-xs text-ink-2 italic" data-testid="relationship-notes">
+								{rel.notes}
+							</p>
+						{/if}
 					</li>
 				{/each}
 			</ul>

frontend/src/routes/persons/[id]/PersonRelationshipsCard.svelte.test.ts

@@ -18,7 +18,9 @@ describe('PersonRelationshipsCard', () => {
 					relatedPersonId: SPOUSE_ID,
 					personDisplayName: 'Anna Müller',
 					relatedPersonDisplayName: 'Bertha Müller',
-					relationType: 'SPOUSE_OF'
+					relationType: 'SPOUSE_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				}
 			],
 			inferredRelationships: [
@@ -65,7 +67,9 @@ describe('PersonRelationshipsCard', () => {
 					relatedPersonId: PARENT_ID,
 					personDisplayName: 'Anna Müller',
 					relatedPersonDisplayName: 'Kind Müller',
-					relationType: 'PARENT_OF'
+					relationType: 'PARENT_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				}
 			],
 			inferredRelationships: []
@@ -84,7 +88,9 @@ describe('PersonRelationshipsCard', () => {
 					relatedPersonId: SPOUSE_ID,
 					personDisplayName: 'Anna',
 					relatedPersonDisplayName: 'Bertha',
-					relationType: 'SPOUSE_OF'
+					relationType: 'SPOUSE_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				}
 			],
 			inferredRelationships: [
@@ -113,7 +119,9 @@ describe('PersonRelationshipsCard', () => {
 					relatedPersonId: PERSON_ID,
 					personDisplayName: 'Eltern Müller',
 					relatedPersonDisplayName: 'Anna Müller',
-					relationType: 'PARENT_OF'
+					relationType: 'PARENT_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
 				}
 			],
 			inferredRelationships: []
@@ -121,4 +129,74 @@ describe('PersonRelationshipsCard', () => {
 
 		await expect.element(page.getByText('Kind von')).toBeInTheDocument();
 	});
+
+	it('renders the date range at its stored precision', async () => {
+		render(PersonRelationshipsCard, {
+			personId: PERSON_ID,
+			relationships: [
+				{
+					id: 'r1',
+					personId: PERSON_ID,
+					relatedPersonId: SPOUSE_ID,
+					personDisplayName: 'Anna Müller',
+					relatedPersonDisplayName: 'Bertha Müller',
+					relationType: 'SPOUSE_OF',
+					fromDate: '1923-05-12',
+					fromDatePrecision: 'DAY',
+					toDatePrecision: 'UNKNOWN'
+				}
+			],
+			inferredRelationships: []
+		});
+
+		await expect
+			.element(page.getByTestId('relationship-date-range'))
+			.toHaveTextContent('12. Mai 1923');
+	});
+
+	it('shows the notes line', async () => {
+		render(PersonRelationshipsCard, {
+			personId: PERSON_ID,
+			relationships: [
+				{
+					id: 'r1',
+					personId: PERSON_ID,
+					relatedPersonId: SPOUSE_ID,
+					personDisplayName: 'Anna Müller',
+					relatedPersonDisplayName: 'Bertha Müller',
+					relationType: 'SPOUSE_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN',
+					notes: 'Hochzeit in Berlin'
+				}
+			],
+			inferredRelationships: []
+		});
+
+		await expect
+			.element(page.getByTestId('relationship-notes'))
+			.toHaveTextContent('Hochzeit in Berlin');
+	});
+
+	it('renders no date line when the relationship has no dates', async () => {
+		render(PersonRelationshipsCard, {
+			personId: PERSON_ID,
+			relationships: [
+				{
+					id: 'r1',
+					personId: PERSON_ID,
+					relatedPersonId: SPOUSE_ID,
+					personDisplayName: 'Anna Müller',
+					relatedPersonDisplayName: 'Bertha Müller',
+					relationType: 'SPOUSE_OF',
+					fromDatePrecision: 'UNKNOWN',
+					toDatePrecision: 'UNKNOWN'
+				}
+			],
+			inferredRelationships: []
+		});
+
+		await expect.element(page.getByText('Bertha Müller')).toBeInTheDocument();
+		expect(document.querySelector('[data-testid="relationship-date-range"]')).toBeNull();
+	});
 });

frontend/src/routes/persons/[id]/edit/+page.server.ts

@@ -2,12 +2,40 @@ import { error, fail, redirect } from '@sveltejs/kit';
 import { createApiClient, extractErrorCode } from '$lib/shared/api.server';
 import { getErrorMessage } from '$lib/shared/errors';
 import type { DatePrecision } from '$lib/shared/utils/documentDate';
+import type { components } from '$lib/generated/api';
 import {
 	normalizePersonType,
 	validatePersonFields,
 	resolveValidationMessage
 } from '$lib/person/person-validation';
 
+type RelationType = NonNullable<components['schemas']['RelationshipUpsertRequest']['relationType']>;
+
+// Parses the shared relationship create/update form into a RelationshipUpsertRequest
+// body. An empty date omits date AND precision so the backend normalises the pair to
+// null/UNKNOWN — a lone precision would fail the coherence check (INVALID_DATE_PRECISION).
+function parseRelationshipForm(formData: FormData) {
+	const relatedPersonId = formData.get('relatedPersonId')?.toString();
+	const relationType = formData.get('relationType')?.toString();
+	const notes = formData.get('notes')?.toString().trim() || undefined;
+	const fromDate = formData.get('fromDate')?.toString().trim() || undefined;
+	const fromDatePrecision = fromDate
+		? (formData.get('fromDatePrecision')?.toString() as DatePrecision)
+		: undefined;
+	const toDate = formData.get('toDate')?.toString().trim() || undefined;
+	const toDatePrecision = toDate
+		? (formData.get('toDatePrecision')?.toString() as DatePrecision)
+		: undefined;
+	const body = {
+		relatedPersonId: relatedPersonId ?? '',
+		relationType: (relationType ?? 'OTHER') as RelationType,
+		...(fromDate ? { fromDate, fromDatePrecision } : {}),
+		...(toDate ? { toDate, toDatePrecision } : {}),
+		...(notes ? { notes } : {})
+	};
+	return { relatedPersonId, relationType, body };
+}
+
 export async function load({ params, fetch, locals }) {
 	const canWrite =
 		(locals.user as { groups?: { permissions: string[] }[] } | undefined)?.groups?.some((g) =>
@@ -193,40 +221,45 @@ export const actions = {
 
 	addRelationship: async ({ request, params, fetch }) => {
 		const formData = await request.formData();
-		const relatedPersonId = formData.get('relatedPersonId')?.toString();
+		const fields = parseRelationshipForm(formData);
-		const relationType = formData.get('relationType')?.toString();
-		const fromYearRaw = formData.get('fromYear')?.toString().trim();
-		const toYearRaw = formData.get('toYear')?.toString().trim();
-		const notes = formData.get('notes')?.toString().trim() || undefined;
 
-		if (!relatedPersonId || !relationType) {
+		if (!fields.relatedPersonId || !fields.relationType) {
 			return fail(400, { relationshipError: getErrorMessage('VALIDATION_ERROR') });
 		}
-		if (relatedPersonId === params.id) {
+		if (fields.relatedPersonId === params.id) {
-			return fail(400, { relationshipError: getErrorMessage('VALIDATION_ERROR') });
-		}
-		const fromYear = fromYearRaw ? parseInt(fromYearRaw, 10) : undefined;
-		const toYear = toYearRaw ? parseInt(toYearRaw, 10) : undefined;
-		if (
-			fromYear !== undefined &&
-			toYear !== undefined &&
-			!Number.isNaN(fromYear) &&
-			!Number.isNaN(toYear) &&
-			toYear < fromYear
-		) {
 			return fail(400, { relationshipError: getErrorMessage('VALIDATION_ERROR') });
 		}
 
 		const api = createApiClient(fetch);
 		const result = await api.POST('/api/persons/{id}/relationships', {
 			params: { path: { id: params.id } },
-			body: {
+			body: fields.body
-				relatedPersonId,
+		});
-				relationType,
+
-				...(fromYear !== undefined && !Number.isNaN(fromYear) ? { fromYear } : {}),
+		if (!result.response.ok) {
-				...(toYear !== undefined && !Number.isNaN(toYear) ? { toYear } : {}),
+			return fail(result.response.status, {
-				...(notes ? { notes } : {})
+				relationshipError: getErrorMessage(extractErrorCode(result.error))
+			});
 		}
+		return { relationshipSuccess: true };
+	},
+
+	updateRelationship: async ({ request, params, fetch }) => {
+		const formData = await request.formData();
+		const relId = formData.get('relId')?.toString();
+		const fields = parseRelationshipForm(formData);
+
+		if (!relId || !fields.relatedPersonId || !fields.relationType) {
+			return fail(400, { relationshipError: getErrorMessage('VALIDATION_ERROR') });
+		}
+		if (fields.relatedPersonId === params.id) {
+			return fail(400, { relationshipError: getErrorMessage('VALIDATION_ERROR') });
+		}
+
+		const api = createApiClient(fetch);
+		const result = await api.PUT('/api/persons/{id}/relationships/{relId}', {
+			params: { path: { id: params.id, relId } },
+			body: fields.body
 		});
 
 		if (!result.response.ok) {

frontend/src/routes/persons/[id]/edit/page.server.spec.ts

@@ -97,3 +97,98 @@ describe('persons/[id]/edit update action — generation (#689)', () => {
 		expect(body).toHaveProperty('generation', 3);
 	});
 });
+
+describe('persons/[id]/edit relationship actions (#837)', () => {
+	function relForm(overrides: Record<string, string | null> = {}): Request {
+		const fd = new FormData();
+		fd.set('relatedPersonId', 'p2');
+		fd.set('relationType', 'SPOUSE_OF');
+		for (const [k, v] of Object.entries(overrides)) {
+			if (v == null) fd.delete(k);
+			else fd.set(k, v);
+		}
+		return new Request('http://localhost/persons/p1/edit', { method: 'POST', body: fd });
+	}
+
+	it('addRelationship posts date + precision + notes', async () => {
+		const post = vi.fn().mockResolvedValue({ response: { ok: true, status: 200 }, data: {} });
+		vi.mocked(createApiClient).mockReturnValue({ POST: post } as unknown as ReturnType<
+			typeof createApiClient
+		>);
+		const request = relForm({
+			fromDate: '1923-05-12',
+			fromDatePrecision: 'DAY',
+			notes: 'Hochzeit'
+		});
+
+		// eslint-disable-next-line @typescript-eslint/no-explicit-any
+		await actions.addRelationship({ request, params: { id: 'p1' }, fetch: mockFetch } as any);
+
+		const [path, opts] = post.mock.calls[0];
+		expect(path).toBe('/api/persons/{id}/relationships');
+		expect(opts.body).toMatchObject({
+			relatedPersonId: 'p2',
+			relationType: 'SPOUSE_OF',
+			fromDate: '1923-05-12',
+			fromDatePrecision: 'DAY',
+			notes: 'Hochzeit'
+		});
+	});
+
+	it('addRelationship omits precision when the date is empty (coherence)', async () => {
+		const post = vi.fn().mockResolvedValue({ response: { ok: true, status: 200 }, data: {} });
+		vi.mocked(createApiClient).mockReturnValue({ POST: post } as unknown as ReturnType<
+			typeof createApiClient
+		>);
+		const request = relForm({ fromDatePrecision: 'DAY' }); // precision but no date
+
+		// eslint-disable-next-line @typescript-eslint/no-explicit-any
+		await actions.addRelationship({ request, params: { id: 'p1' }, fetch: mockFetch } as any);
+
+		const body = post.mock.calls[0][1].body;
+		expect(body).not.toHaveProperty('fromDate');
+		expect(body).not.toHaveProperty('fromDatePrecision');
+	});
+
+	it('updateRelationship PUTs to the relId path with the new body', async () => {
+		const put = vi.fn().mockResolvedValue({ response: { ok: true, status: 200 }, data: {} });
+		vi.mocked(createApiClient).mockReturnValue({ PUT: put } as unknown as ReturnType<
+			typeof createApiClient
+		>);
+		const request = relForm({ relId: 'rel-9', fromDate: '1923-05-12', fromDatePrecision: 'DAY' });
+
+		// eslint-disable-next-line @typescript-eslint/no-explicit-any
+		await actions.updateRelationship({ request, params: { id: 'p1' }, fetch: mockFetch } as any);
+
+		const [path, opts] = put.mock.calls[0];
+		expect(path).toBe('/api/persons/{id}/relationships/{relId}');
+		expect(opts.params.path).toMatchObject({ id: 'p1', relId: 'rel-9' });
+		expect(opts.body).toMatchObject({
+			relatedPersonId: 'p2',
+			relationType: 'SPOUSE_OF',
+			fromDate: '1923-05-12',
+			fromDatePrecision: 'DAY'
+		});
+	});
+
+	it('updateRelationship surfaces a backend error as a fail', async () => {
+		const put = vi.fn().mockResolvedValue({
+			response: { ok: false, status: 400 },
+			error: { code: 'INVALID_RELATIONSHIP_DATES' }
+		});
+		vi.mocked(createApiClient).mockReturnValue({ PUT: put } as unknown as ReturnType<
+			typeof createApiClient
+		>);
+		const request = relForm({ relId: 'rel-9' });
+
+		const result = (await actions.updateRelationship({
+			request,
+			params: { id: 'p1' },
+			fetch: mockFetch
+			// eslint-disable-next-line @typescript-eslint/no-explicit-any
+		} as any)) as { status: number; data: { relationshipError: string } };
+
+		expect(result.status).toBe(400);
+		expect(result.data.relationshipError).toBeTruthy();
+	});
+});

frontend/src/routes/zeitstrahl/+page.svelte

@@ -1,14 +1,50 @@
 <script lang="ts">
 import * as m from '$lib/paraglide/messages.js';
 import TimelineView from '$lib/timeline/TimelineView.svelte';
+import TimelineFilters from '$lib/timeline/TimelineFilters.svelte';
+import GroupingControl from '$lib/timeline/GroupingControl.svelte';
 import { timelineMeta } from '$lib/timeline/timelineMeta';
+import { filterTimeline } from '$lib/timeline/timelineFilter';
+import { hasLooseLetters, type GroupingMode } from '$lib/timeline/timelineGrouping';
 import type { PageData } from './$types';
 
 let { data }: { data: PageData } = $props();
 
-const meta = $derived(timelineMeta(data.timeline));
 const hasContent = $derived(data.timeline.years.length > 0 || data.timeline.undated.length > 0);
 
+// Layer-filter state (#780). Layer hiding is client-side only — the whole
+// timeline is loaded once by #779's SSR load and we derive a filtered view of
+// it here; there is no goto, no URL param, and no extra fetch.
+let personalOn = $state(true);
+let historicalOn = $state(true);
+let lettersOn = $state(true);
+
+// Grouping state (#827) lives here beside the layer-filter state; the regroup is a
+// pure client-side transform over the already-filtered view — filter-then-group.
+let groupingMode = $state<GroupingMode>('date');
+
+const filteredTimeline = $derived(
+	filterTimeline(data.timeline, { personalOn, historicalOn, lettersOn })
+);
+const filteredEmpty = $derived(
+	filteredTimeline.years.length === 0 && filteredTimeline.undated.length === 0
+);
+// The grouping control is only meaningful while loose letters remain in the filtered
+// view; with the Letters layer off there is nothing to regroup, so it disables but
+// keeps its selected mode (REQ-018).
+const hasLetters = $derived(hasLooseLetters(filteredTimeline));
+
+// Meta-line figures track the *filtered* view, so the header counts always
+// match what is actually on screen once layers are toggled off (#780 — this
+// closes the prior D1 limitation, where the counts stayed on the full timeline).
+const meta = $derived(timelineMeta(filteredTimeline));
+
+function resetFilters() {
+	personalOn = true;
+	historicalOn = true;
+	lettersOn = true;
+}
+
 // Compose the sub-line from segments joined by " · " so the range drops out
 // cleanly when there are no year bands; the whole line is absent when the
 // timeline is empty (REQ-002). Counts come from the route alone, never from
@@ -34,7 +70,13 @@ const metaLine = $derived.by(() => {
 				: m.timeline_events_count({ count: meta.eventCount })
 		);
 	}
-	segments.push(m.timeline_grouping_date());
+	segments.push(
+		groupingMode === 'event'
+			? m.timeline_grouping_event()
+			: groupingMode === 'thema'
+				? m.timeline_grouping_thema()
+				: m.timeline_grouping_date()
+	);
 	return segments.join(' · ');
 });
 </script>
@@ -48,10 +90,56 @@ const metaLine = $derived.by(() => {
 	     border is intentionally omitted (the page is already bg-canvas), per the
 	     review of REQ-001 — the sheet reads through its padding, not a frame line. -->
 	<div data-testid="timeline-canvas" class="rounded-[10px] bg-canvas p-6">
+		<!-- Wrapping header so the CTA drops below the heading at narrow widths
+		     (≤360px) instead of overflowing — #842 REQ-001. -->
+		<header class="flex flex-wrap items-center justify-between gap-3">
 			<h1 class="font-serif text-2xl font-bold text-brand-navy">{m.timeline_heading()}</h1>
-		{#if hasContent}
+			{#if data.canWrite}
-			<p data-testid="timeline-meta" class="mt-1 mb-6 font-sans text-xs text-ink-3">{metaLine}</p>
+				<a
+					data-testid="timeline-add-event"
+					href="/zeitstrahl/events/new"
+					class="inline-flex h-11 items-center rounded bg-primary px-4 font-sans text-sm font-medium text-primary-fg hover:opacity-90 focus:outline-none focus-visible:ring-2 focus-visible:ring-focus-ring"
+				>
+					{m.timeline_add_event()}
+				</a>
+			{/if}
+		</header>
+		{#if hasContent}
+			<p data-testid="timeline-meta" class="mt-1 mb-3 font-sans text-xs text-ink-3">{metaLine}</p>
+			<!-- Grouping toggle stacked above the #780 layer-filter trigger so the two read as
+			     one control cluster in the header (REQ-010); the top-right corner stays the
+			     add-event CTA. Disabled — but kept in place — when no loose letters remain
+			     (REQ-018). -->
+			<div class="mb-3" data-testid="grouping-cluster">
+				<GroupingControl bind:mode={groupingMode} disabled={!hasLetters} />
+			</div>
+			<TimelineFilters
+				bind:personalOn={personalOn}
+				bind:historicalOn={historicalOn}
+				bind:lettersOn={lettersOn}
+			/>
+		{/if}
+		{#if hasContent && filteredEmpty}
+			<!-- Filtered-empty: a calm message + one-click reset below the still-open
+			     filter bar — never a blank page, and never the generic "no events"
+			     state (which would imply the archive itself is empty). REQ-006. -->
+			<div data-testid="timeline-filter-empty" class="py-12 text-center">
+				<p class="font-serif text-base text-ink-2">{m.timeline_filter_empty_state()}</p>
+				<button
+					type="button"
+					data-testid="timeline-filter-empty-reset"
+					onclick={resetFilters}
+					class="mt-3 inline-flex min-h-[44px] items-center font-sans text-sm text-primary underline-offset-2 hover:underline"
+				>
+					{m.timeline_filter_reset()}
+				</button>
+			</div>
+		{:else}
+			<TimelineView
+				timeline={filteredTimeline}
+				canWrite={data.canWrite}
+				groupingMode={groupingMode}
+			/>
 		{/if}
-		<TimelineView timeline={data.timeline} />
 	</div>
 </div>

frontend/src/routes/zeitstrahl/page.svelte.spec.ts

@@ -1,5 +1,6 @@
 import { describe, it, expect, afterEach } from 'vitest';
 import { cleanup, render } from 'vitest-browser-svelte';
+import { page } from 'vitest/browser';
 import * as m from '$lib/paraglide/messages.js';
 import Page from './+page.svelte';
 import { makeEntry, makeYear, makeTimelineDTO } from '$lib/timeline/test-factories';
@@ -111,3 +112,214 @@ describe('/zeitstrahl page', () => {
 		expect(sub?.textContent).not.toContain(m.timeline_events_count({ count: 1 }));
 	});
 });
+
+describe('/zeitstrahl layer filter (#780)', () => {
+	const letter = (title: string, documentId: string) => makeEntry({ documentId, title });
+	const historical = (title: string) =>
+		makeEntry({
+			kind: 'EVENT',
+			type: 'HISTORICAL',
+			derived: false,
+			eventId: 'h1',
+			documentId: undefined,
+			title,
+			senderName: '',
+			receiverName: ''
+		});
+	const personal = (title: string) =>
+		makeEntry({
+			kind: 'EVENT',
+			type: 'PERSONAL',
+			derived: false,
+			eventId: 'p1',
+			documentId: undefined,
+			title,
+			senderName: '',
+			receiverName: ''
+		});
+
+	const mixed = () =>
+		makeTimelineDTO({
+			years: [
+				makeYear(1915, [
+					letter('Brief Eins', 'd1'),
+					historical('Erster Weltkrieg'),
+					personal('Umzug nach Berlin')
+				])
+			]
+		});
+
+	async function openBar() {
+		await page.getByTestId('timeline-filter-trigger').click();
+	}
+
+	it('hides letter cards when the Letters layer is off and restores them, with no fetch (REQ-005/002)', async () => {
+		render(Page, { data: pageData(mixed()) });
+		await expect.element(page.getByText('Brief Eins')).toBeVisible();
+		await openBar();
+		await page.getByTestId('timeline-filter-letters').click();
+		await expect.poll(() => page.getByText('Brief Eins').query()).toBeNull();
+		await expect.element(page.getByText('Umzug nach Berlin')).toBeVisible();
+		await page.getByTestId('timeline-filter-letters').click();
+		await expect.element(page.getByText('Brief Eins')).toBeVisible();
+	});
+
+	it('hides historical event cards when the Historical layer is off (REQ-004)', async () => {
+		render(Page, { data: pageData(mixed()) });
+		await openBar();
+		await page.getByTestId('timeline-filter-historical').click();
+		await expect.poll(() => page.getByText('Erster Weltkrieg').query()).toBeNull();
+		await expect.element(page.getByText('Brief Eins')).toBeVisible();
+		await expect.element(page.getByText('Umzug nach Berlin')).toBeVisible();
+	});
+
+	it('hides personal event cards when the Personal layer is off (REQ-003)', async () => {
+		render(Page, { data: pageData(mixed()) });
+		await openBar();
+		await page.getByTestId('timeline-filter-personal').click();
+		await expect.poll(() => page.getByText('Umzug nach Berlin').query()).toBeNull();
+		await expect.element(page.getByText('Brief Eins')).toBeVisible();
+		await expect.element(page.getByText('Erster Weltkrieg')).toBeVisible();
+	});
+
+	it('shows the filtered-empty message + reset below the open bar when all layers are off (REQ-006)', async () => {
+		render(Page, { data: pageData(mixed()) });
+		await openBar();
+		await page.getByTestId('timeline-filter-personal').click();
+		await page.getByTestId('timeline-filter-historical').click();
+		await page.getByTestId('timeline-filter-letters').click();
+		await expect.element(page.getByText(m.timeline_filter_empty_state())).toBeVisible();
+		await expect.element(page.getByTestId('timeline-filter-empty-reset')).toBeVisible();
+		// the generic TimelineView empty state is never what shows for a filtered-empty view
+		expect(page.getByText(m.timeline_empty_state()).query()).toBeNull();
+		// the one-click reset restores every layer
+		await page.getByTestId('timeline-filter-empty-reset').click();
+		await expect.element(page.getByText('Brief Eins')).toBeVisible();
+	});
+
+	it('recomputes the meta-line counts from the filtered view, so a hidden layer drops out of the totals (#780, resolves D1)', async () => {
+		render(Page, { data: pageData(mixed()) });
+		const meta = page.getByTestId('timeline-meta');
+		// all layers on → the one letter and the two events are counted
+		await expect.element(meta).toHaveTextContent(m.timeline_letters_count_singular());
+		await expect.element(meta).toHaveTextContent(m.timeline_events_count({ count: 2 }));
+
+		await openBar();
+		await page.getByTestId('timeline-filter-letters').click();
+
+		// the hidden letter leaves the count instead of lingering as "1 Brief";
+		// the event total is untouched
+		await expect.element(meta).not.toHaveTextContent(m.timeline_letters_count_singular());
+		await expect.element(meta).toHaveTextContent(m.timeline_events_count({ count: 2 }));
+	});
+});
+
+describe('/zeitstrahl curator affordances (#842)', () => {
+	const curated = (eventId: string) =>
+		makeEntry({
+			kind: 'EVENT',
+			type: 'PERSONAL',
+			derived: false,
+			eventId,
+			title: 'Auswanderung',
+			senderName: '',
+			receiverName: '',
+			documentId: undefined
+		});
+
+	const withWrite = (timeline: ReturnType<typeof makeTimelineDTO>) => ({
+		...pageData(timeline),
+		canWrite: true
+	});
+
+	it('renders the add-event CTA in a wrapping header when the viewer can write (REQ-001)', () => {
+		render(Page, { data: withWrite(makeTimelineDTO({ years: [makeYear(1909, [makeEntry()])] })) });
+		const add = document.querySelector(
+			'[data-testid="timeline-add-event"]'
+		) as HTMLAnchorElement | null;
+		expect(add).not.toBeNull();
+		expect(add?.getAttribute('href')).toBe('/zeitstrahl/events/new');
+		// The header wraps so the CTA drops below the heading at narrow widths (≤360px)
+		// rather than overflowing — REQ-001.
+		expect(add?.closest('header')?.classList.contains('flex-wrap')).toBe(true);
+	});
+
+	it('renders no add-event CTA when the viewer cannot write (REQ-002)', () => {
+		render(Page, {
+			data: pageData(makeTimelineDTO({ years: [makeYear(1909, [makeEntry()])] }))
+		});
+		expect(document.querySelector('[data-testid="timeline-add-event"]')).toBeNull();
+	});
+
+	it('threads canWrite to the timeline so a curator sees an event edit link (REQ-001/009)', () => {
+		render(Page, {
+			data: withWrite(makeTimelineDTO({ years: [makeYear(1924, [curated('p9')])] }))
+		});
+		expect(document.querySelector('a[href="/zeitstrahl/events/p9/edit"]')).not.toBeNull();
+	});
+
+	it('shows no event edit link to a reader (REQ-007)', () => {
+		render(Page, {
+			data: pageData(makeTimelineDTO({ years: [makeYear(1924, [curated('p9')])] }))
+		});
+		expect(document.querySelector('[data-testid="event-edit"]')).toBeNull();
+	});
+});
+
+describe('/zeitstrahl grouping toggle (#827)', () => {
+	const historical = () =>
+		makeEntry({
+			kind: 'EVENT',
+			type: 'HISTORICAL',
+			derived: false,
+			eventId: 'h1',
+			documentId: undefined,
+			title: 'Erster Weltkrieg',
+			senderName: '',
+			receiverName: ''
+		});
+	const mixed = () =>
+		makeTimelineDTO({
+			years: [
+				makeYear(1915, [
+					makeEntry({ documentId: 'd1', title: 'Brief Eins', linkedEventId: 'h1' }),
+					historical()
+				])
+			]
+		});
+	const radio = (value: string) => document.querySelector(`[data-value="${value}"]`) as HTMLElement;
+
+	it('updates the meta-line grouping label when a mode is chosen (REQ-016)', async () => {
+		render(Page, { data: pageData(mixed()) });
+		const meta = page.getByTestId('timeline-meta');
+		await expect.element(meta).toHaveTextContent(m.timeline_grouping_date());
+		radio('event').click();
+		await expect.element(meta).toHaveTextContent(m.timeline_grouping_event());
+		radio('thema').click();
+		await expect.element(meta).toHaveTextContent(m.timeline_grouping_thema());
+	});
+
+	it('regroups loose letters under their event client-side, no buckets in Datum (REQ-002/003)', async () => {
+		render(Page, { data: pageData(mixed()) });
+		expect(document.querySelector('[data-testid="letter-bucket"]')).toBeNull();
+		radio('event').click();
+		await expect.element(page.getByTestId('letter-bucket')).toBeVisible();
+	});
+
+	it('disables the grouping control when the Letters layer is off, keeping the mode (REQ-018)', async () => {
+		render(Page, { data: pageData(mixed()) });
+		radio('thema').click();
+		const control = page.getByTestId('grouping-control');
+		await expect.element(control).toHaveAttribute('aria-disabled', 'false');
+		// turn the Letters layer off → nothing to regroup
+		await page.getByTestId('timeline-filter-trigger').click();
+		await page.getByTestId('timeline-filter-letters').click();
+		await expect.element(control).toHaveAttribute('aria-disabled', 'true');
+		// the chosen mode is retained for when letters return
+		expect(radio('thema').getAttribute('aria-checked')).toBe('true');
+		// re-enabling restores the enabled control with the same mode (no reset to Datum)
+		await page.getByTestId('timeline-filter-letters').click();
+		await expect.element(control).toHaveAttribute('aria-disabled', 'false');
+		expect(radio('thema').getAttribute('aria-checked')).toBe('true');
+	});
+});