B4 — jsdom-runnable assertions for the structural pieces of B2/B3.
apps/app/tests/unit/lib/timetable/row-height.test.ts (4 tests):
- laneCount=0 → 52px (Math.max(1, 0) fallback path)
- laneCount=1 → 52px (single-lane stage row)
- laneCount=3 → 148px
- laneCount=10 → 484px (10 × 48 + 4)
apps/app/tests/component/StageHeaderCell.test.ts (4 tests):
- row-height-px prop applies as inline blockSize on the root
- prop omitted → no inline blockSize set (legacy `block-size: 100%`
CSS path takes over for any caller still relying on parent-driven sizing)
- 484px for laneCount=10 round-trips through the prop without truncation
- conflict badge renders only when conflictCount > 0 (existing behavior;
locked in as part of touching this surface)
Visual scroll/alignment proof (sticky-left freeze pane, sticky-top axis,
horizontal scroll cohesion across 14 stages, diagonal trackpad scroll,
pixel-perfect header↔row alignment) is deferred to TEST-VISUAL-001
explicitly: jsdom does not compute position:sticky offsets, scrollbar
visibility, layout overflow chains, or scroll containment ancestry. This
is a known limitation of jsdom-based component testing — not a test gap
in this branch. The sticky behavior, z-index ladder, and DOM structure
are all in place per E1-E4; their validation requires a real browser,
which is exactly what the Playwright CT migration on TEST-INFRA-001 +
TEST-VISUAL-001 unlocks.
No existing tests asserted the old broken layout (no references to the
deprecated `tt-page__rows`, `tt-page__stages`, or `<GridBg>` in tests/).
The unused GridBg component file remains on disk; deleting it is a
stylistic cleanup outside this stabilization scope.
Test count: 389 → 397.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
