fix(timeline): track the meta-line counts to the filtered view

The /zeitstrahl header sub-line counted the unfiltered timeline, so a
hidden layer (e.g. Letters off) still showed its entries in the totals
("1 Brief" with no letters on screen) — the documented D1 limitation.
Derive the meta from filteredTimeline so the range and letter/event
counts always match what is actually rendered. hasContent stays on the
full timeline so the filter bar and meta line still appear whenever the
archive has content.

Refs #780

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.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

@@ -173,3 +173,13 @@
 | 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 |

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/messages/de.json

@@ -1057,6 +1057,14 @@
 	"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",

frontend/messages/en.json

@@ -1057,6 +1057,14 @@
 	"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",

frontend/messages/es.json

@@ -1057,6 +1057,14 @@
 	"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",

frontend/src/lib/messages.spec.ts

@@ -98,4 +98,29 @@ 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}');
+	});
 });

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/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/routes/zeitstrahl/+page.svelte

@@ -1,14 +1,40 @@
 <script lang="ts">
 import * as m from '$lib/paraglide/messages.js';
 import TimelineView from '$lib/timeline/TimelineView.svelte';
+import TimelineFilters from '$lib/timeline/TimelineFilters.svelte';
 import { timelineMeta } from '$lib/timeline/timelineMeta';
+import { filterTimeline } from '$lib/timeline/timelineFilter';
 import type { PageData } from './$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);
+
+const filteredTimeline = $derived(
+	filterTimeline(data.timeline, { personalOn, historicalOn, lettersOn })
+);
+const filteredEmpty = $derived(
+	filteredTimeline.years.length === 0 && filteredTimeline.undated.length === 0
+);
+
+// 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
@@ -51,7 +77,29 @@ const metaLine = $derived.by(() => {
 		<h1 class="font-serif text-2xl font-bold text-brand-navy">{m.timeline_heading()}</h1>
 		{#if hasContent}
 			<p data-testid="timeline-meta" class="mt-1 mb-6 font-sans text-xs text-ink-3">{metaLine}</p>
+			<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} />
 		{/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 +112,104 @@ 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 }));
+	});
+});