# ADR-026 — In-House Stammbaum Layout, dagre Evaluated and Deferred

**Date:** 2026-05-28
**Status:** Accepted
**Issue:** #361
**Supersedes:** _none_
**Supersedes-on-trigger:** A future ADR-027 if any acceptance criterion below stops converging in-house.

---

## Context

After #689 shipped the seeded-rank invariant — `buildLayout.ts` treats imported
`persons.generation` as a strict row anchor and the iterative heuristic only
runs for unseeded nodes — the question "should we adopt
[@dagrejs/dagre](https://www.npmjs.com/package/@dagrejs/dagre) for Stammbaum
layout?" had to be re-evaluated.

dagre's headline value is **rank assignment** via `network-simplex` /
`longest-path`. That value is now mostly redundant: curated import data already
pins ranks for the family graph, and the residual heuristic only places
unseeded nodes (today: family members imported without a `generation` column,
spouses with no parents in the graph).

What remains are **position-within-rank** problems:

1. Multi-spouse persons (canonical case: Albert de Gruyter, 4 marriages) whose
   secondary marriages were silently dropped by a `Map<string, string>` shape.
2. Intra-family marriages — two persons in different sibling blocks at the
   same rank who marry each other (latent; zero cases in current data).
3. Unseeded loose spouses whose parents are also in the graph (latent; zero
   cases — 0 of 942 unseeded persons match the predicate in the May-2026
   snapshot).

Six persona walkthroughs on #361 (Leonie/UX, Felix/Dev, Markus/Architect,
Nora/Security, Sara/QA, Tobias/DevOps, Elicit/Requirements) converged on the
same recommendation: try the in-house fix path first, against the canonical
dataset, with quantitative exit triggers — adopt dagre only if any acceptance
criterion fails to converge.

---

## Decision

**Keep Stammbaum layout in-house. Do not adopt dagre at this time.**

The fix path lands as six commits on #361:

1. Spec geometry reconcile (`NODE_W=160, NODE_H=56` matches `buildLayout.ts`)
   and an explicit seeded-rank-invariant Layout-rules line.
2. Canonical `/api/network` fixture capture script + pinned snapshot for
   structural assertions in `buildLayout.test.ts`.
3. `spousePairs: Map<string, string>` → `Map<string, Set<string>>`. Preserves
   all marriages; closes Nora's robustness gap (edges referencing IDs outside
   `allNodes` are guarded at ingestion).
4. Multi-spouse ordering: `(fromYear ASC NULLS LAST, displayName ASC)`,
   inserted to the right of the parented focal — matches Leonie's UX rule.
5. Intra-family-marriage block merge across same-rank parented sibling blocks
   (AC2) — adjacent placement at the join boundary.
6. Marriage-line midpoint dot enlarged from `r=4.5` to `r=6` (WCAG 1.4.11
   informational contrast — the dot disambiguates stacked marriages and is
   no longer decorative).

The block-packer + AC2 merge stays well under Markus's 80-LoC extraction
threshold, so `packBlocks.ts` is **not** yet warranted.

---

## Consequences

### Accepted today

- **AC1 (multi-spouse preservation)** is now a property of `buildLayout`, verified
  by both synthetic and canonical fixture tests.
- **AC2 (intra-family marriage)** ships latent but covered by a synthetic
  two-family regression test.
- **AC4 (seeded-rank invariant)** preserved end-to-end by every `buildLayout.test.ts`
  case from #689.
- **AC5 (spec ↔ code geometry)** reconciled in commit 1.

### Deferred with revisit triggers

- **AC3 — Unseeded loose spouse with parents-in-graph.** Database verification:
  0 of 942 unseeded persons match the predicate today. Structurally, every
  realistic case maps to a **curation/import gap** (P's parents were imported
  with `generation`, P themselves was not) and belongs in the canonical import
  sheet rather than `buildLayout`. **Revisit trigger:** first canonical fixture
  containing a parented unseeded spouse — at which point this ADR is updated
  in place or superseded by an ADR-027. **Reproducible verification query**
  (PostgreSQL — paste into a read-only psql session against
  `familienarchiv_archive`):

  ```sql
  -- AC3 reachability probe. Returns one row per unseeded person who has at
  -- least one parent edge whose parent IS seeded. A non-zero count means the
  -- AC3 layout branch becomes reachable for that person and ADR-026 should
  -- be revisited. Last run May 2026: 0 rows.
  SELECT p.id, p.display_name
  FROM persons p
  WHERE p.generation IS NULL
    AND EXISTS (
        SELECT 1
        FROM person_relationships r
        JOIN persons parent ON parent.id = r.person_id
        WHERE r.relation_type = 'PARENT_OF'
          AND r.related_person_id = p.id
          AND parent.generation IS NOT NULL
    );
  ```

  The same predicate is encoded as a unit-testable JavaScript function — see
  `findAc3Candidates()` in
  `frontend/src/lib/person/genealogy/__fixtures__/findAc3Candidates.mjs`,
  asserted against the committed canonical fixture by
  `validateFixture.test.ts`, and emitted as a stderr soft-warn by
  `frontend/scripts/capture-network-fixture.mjs` on every recapture. The SQL
  is the source-of-truth probe against live data; the function is the
  capture-time and fixture-time signal that the predicate's count crossed
  zero.
- **AC6 — Bundle-impact gate (≤ 40 kB gzipped on `/stammbaum`).** Moot under
  this ADR; reactivates only under ADR-027 (dagre adoption).
- **AC7 — Visual regression at 320 / 768 / 1440.** `toHaveScreenshot()`
  permanently dropped (high running cost, speculative coverage). The axe-core
  3:1 contrast check for the enlarged marriage dot is verified one-shot at
  PR time, not committed; the permanent contrast/breakpoint gate lands with
  #692 (mobile pan/zoom epic) alongside the breakpoint visual-regression
  infrastructure.

### UX-signal-only stop trigger for dagre adoption

There is **no LoC cap** on the in-house path. The only divergence signal that
warrants reopening the dagre decision is a **UX failure against the canonical
fixture** — specifically, Albert de Gruyter's 4 marriages failing the read
test ("can a 67-year-old researcher unambiguously see all four spouses?").
If that ever happens, Felix posts a divergence-evidence comment on #361 (or
the equivalent successor issue), the team re-runs brainstorming with the
dagre option on the table, and adoption proceeds under the supply-chain
controls already documented in #361's body (`@dagrejs/dagre` exact-pinned, no
auto-merge, try/catch fallback with structured log, deterministic input sort).

### Operational

- **No CI, image, or compose changes.** Pure frontend layout work; standard
  frontend rebuild covers the deploy.
- **No service topology changes.** No new env vars, ports, resource limits.

---

## Notes

- `frontend/scripts/capture-network-fixture.mjs` is a **local-only developer
  utility**, never invoked from CI. Re-run intentionally; commit the resulting
  JSON in one atomic commit when a new structural case appears (new edge type,
  new marriage configuration, new generation range).
- The canonical fixture contains real family names. Repository is private;
  scrubbing is a single-commit migration if it ever opens.
- Brand-mint enforcement on SVG strokes (Leonie's "all connectors render in
  brand-navy, hierarchy comes from shape") stays a **code-review check at PR
  time**. No CI grep, no custom ESLint rule.
- **Revisit cadence.** Re-evaluate dagre adoption on the first canonical
  fixture refresh that hits AC3, OR by 2027-05-01 at the latest. Owner: Felix
  Brandt.
