Spec — Visual regression TDDs

Scope

Every interactive Koder surface MUST ship the three TDD categories below under tests/regression/visual/. Targets:

• Web: docs site, landing pages, web apps (admin/dashboards).
• Flutter: mobile + desktop + web + TV.
• Android native: Kotlin/Compose apps.
• iOS native: when shipped.
• CLI / TUI: column-width adaptation only (category C overflow variant); other categories N/A.

Out of scope: static text files, server-only services with no UI, markdown rendered without page chrome.

R1 — Categories (the four TDDs)

Category A — Viewport overflow

For every named layout state (default, drawer-open, modal-open, keyboard-open, etc.) at every R2 viewport, assert that no rendered element crosses the viewport edge. Concretely:

∀ element e ∈ document.querySelectorAll('*'):
  rect = e.getBoundingClientRect()
  assert rect.right  ≤ viewport.width
  assert rect.left   ≥ 0
  assert rect.bottom ≤ visualViewport.height + scrollY
  assert rect.top    ≥ 0 - scrollY

Exemptions: explicitly opted-out elements may carry the data attribute data-visual-overflow="allowed-by:<spec-ref>" (e.g. allowed-by:components/carousel.kmd § R3 marquee). Audit reads the attribute and skips. No unmarked exemptions — bugs hide there.

Category B — Chrome overlap

Specifically tests dynamic chrome that grows / shrinks at runtime:

• Web mobile (Chrome / Safari): URL bar enters during scroll-up. Test that position: fixed; bottom: 0 controls + last items of sidebar drawers + bottom sheets + FABs stay reachable.
• iOS Safari: home indicator gesture area.
• Android system chrome: status bar, 3-button nav bar, gesture pill, IME (keyboard).
• Display cutouts: notch, hole-punch, Dynamic Island in landscape.

Required assertions, per viewport per chrome state:

1. The last item of any drawer/sidebar is fully visible — lastChild.getBoundingClientRect().bottom ≤ visualViewport.height.
2. No critical control sits under chrome — buttons, links, form fields tested for intersection with the chrome regions reported by the OS or simulated by the test harness (window.visualViewport for web, MediaQuery.viewPadding for Flutter).
3. 100dvh containers shrink correctly — web only; if the layout sets height: 100vh (no dvh fallback above it) the assertion fails with a hint pointing to specs/app-layout/safe-area.kmd § Web.

Category C — Decorative-element proportion

Decorative shapes (hero blobs, mascot illustrations, divider ornaments) must scale proportionally to their container, NOT bottom out on a fixed min value that overshoots small viewports.

Assertions:

1. No element with data-kds-decorative="true" exceeds 33% of its container width on Compact (< 600 dp) viewports.

2. Visual-area parity — sibling decoratives in the same row must not differ in perceived width by more than 12% (`Math.abs(a.width

   • b.width) / Math.max(a.width, b.width) ≤ 0.12`).

3. clamp() floor sanity — extract the px floor of every width: clamp(MIN, vw, MAX) declaration. Floor MUST be ≤ vw value at 360 dp viewport (otherwise the floor wins and the shape doesn't scale below tablet). Audit grep: tools/koder-css-audit clamp-floor --viewport 360.

4. Decorative margin — silhouette never touches container edges. Per viewport in R2, for every data-kds-decorative="true" element measure getBoundingClientRect() against its nearest positioned ancestor (the "container"). Assert:

   • At rest: rect.top ≥ container.top + 4% × container.height
   • At rest: rect.bottom ≤ container.bottom − 4% × container.height
   • At rest: rect.left ≥ container.left + 4% × container.width
   • At rest: rect.right ≤ container.right − 4% × container.width
   • At every keyframe peak (sample at 25 / 50 / 75% of each named animation), the same 4% margin holds. The harness drives Element.getAnimations()[i].currentTime to each peak before measuring.

   Rationale: keyframe peaks routinely push silhouettes past the resting bounding box (translate Y −55%, scale 1.15 etc.); checking only with animation-play-state: paused misses the worst frames. The 4% floor is a soft minimum — designers may raise it per surface via --kds-decorative-margin: 6%; on the container, which the audit reads via getComputedStyle(container).getPropertyValue(...).

Category D — Sibling decorative collision

Decorative siblings (hero shapes, mascot trio, illustration cluster) inside the same positioned container MUST NOT pile onto each other when the viewport shrinks. Category C guarantees each shape stays within its own clamp budget; Category D guarantees the cluster remains visually parseable as N separate shapes.

Concretely, for every container holding ≥ 2 elements with data-kds-decorative="true" (or matching the same data-kds-decorative-group="<name>"), per viewport in R2:

∀ par (a, b) de shapes irmãs no mesmo container, em cada keyframe peak:
  rect_a = a.getBoundingClientRect()
  rect_b = b.getBoundingClientRect()
  overlap_area = max(0, min(a.right, b.right) - max(a.left, b.left))
               × max(0, min(a.bottom, b.bottom) - max(a.top, b.top))
  min_area = min(rect_a.width × rect_a.height, rect_b.width × rect_b.height)
  assert overlap_area / min_area ≤ 0.05      # ≤ 5% of the smaller shape

Floor is 5% of the smaller shape's area — small grazing touch (decorative blend) tolerated; pile-on (the pink-blue-yellow trio in the user-reported #057 KDS hero bug at 390 dp) flagged. Surface may raise the floor per-container with --kds-decorative-collision-floor: 12%; for intentional overlapping collages (audit reads via getComputedStyle); raising the floor requires a spec § reference in the same PR (mirror R6 allow-list rule).

Run at the 3 phone rows of R2 plus phone-360l (landscape — notch state often triggers extra collision). Sample at keyframe peaks via the same Element.getAnimations() mechanism as Category C R1.C.4.

Rationale: a hero cluster sized for desktop (3 shapes laid out horizontally with 24 dp gaps) collapses to a vertical-ish pile on a 360 dp portrait viewport when the container narrows below the sum of the shapes' min widths. Either the layout reflows (preferable — column stack with gap reset) or the shapes scale down further (must preserve gap proportionally). Category D fails on both regression modes; the fix is structural, not per-shape clamp tweaks.

R2 — Test viewport matrix (mandatory)

Mirrors docs-mobile-responsiveness.kmd § R5 extended with two landscape rows:

CI MUST run categories A and B at every row. Category C runs at the 3 phone rows (decoratives matter on the floor). Category D runs at the 3 phone rows + phone-360l (landscape notch surfaces extra collision states).

R3 — Chrome states to enumerate (Category B)

Per R2 phone row, simulate each chrome state:

The audit harness drives the viewport through every state and runs the A/B assertions for each.

R4 — Generation contract

/k-test (TDD generator) MUST emit the visual-regression suite when the module has any of:

• A koder.toml [ui] block declaring surfaces = [...].
• A pubspec.yaml with flutter SDK dep.
• A package.json with react, vue, svelte, @playwright/test, templ (Go), or @koder/web-kit dep.
• An android/app/src/main/AndroidManifest.xml with <activity>.

Generated tests live under <module>/tests/regression/visual/. File naming: <viewport-id>-<category>.spec.{ts,dart,kt}. Snapshots live in the sibling __snapshots__/ directory and ARE committed (per policies/regression-tests.kmd — snapshots are golden, not artifacts).

Template engines:

• Web → Playwright + the snippet in specs/web-apps/responsive-smoke.test.js, extended with category A/B/C assertions.
• Flutter → flutter_test + golden_toolkit for snapshots + MediaQuery overrides for viewport states.
• Android native → Compose UI Test (createComposeRule()) with setContent + onRoot().assertExists() overflow checks.

R5 — Run cadence

R6 — Allow-list anti-pattern

If a bug is found that the audit doesn't catch, the fix is to add a new assertion, not to allow-list the failing element. Allow-list entries (R1 data-visual-overflow attribute) require a spec reference and reviewer sign-off (PR description must link the spec § allowing the exemption).

R7 — Existing live gaps (snapshot at ratification)

At time of ratification (2026-05-21), the following surfaces have NO visual-regression suite:

• tools/design-gen (KDS docs site) — depended on Lighthouse Mobile
  • manual review. Gap caught by user-reported bugs same day: (1) hero shapes overshooting bounding box at 22vw / 18vw clamp floors on Compact, (2) sidebar drawer last item clipped by Chrome Android URL bar, (3) topbar gear icon clipping right viewport edge, (4) hero-shape trio (pink square + blue triangle + yellow circle) piling onto each other at 390 dp portrait — caught by new Category D (item 4 added 2026-05-21 evening following user- reported mobile screenshot). Open ticket: tools/design-gen#057 follow-up.
• All engines/sdk/koder_kit Flutter consumers — handled by KoderSafeScaffold for chrome, but no overflow audit.
• All Android native apps — manual screenshot review only.

Track closure in meta/docs/stack/registries/visual-regression-coverage.md (new — created with this spec).

Tests of the test contract

Relationship to existing specs

• Subset, not duplicate, of docs-mobile-responsiveness.kmd §R4 — that spec covers Lighthouse-scope structural checks; this spec adds per-element overflow / chrome / proportion.
• Cross-references safe-area.kmd — chrome overlap (Category B) uses the same insets API; this spec adds the test that verifies consumption.
• Bound by policies/regression-tests.kmd — fix-without-test rule applies: any visual fix must ship a Category-A/B/C test that would have caught it.

Open follow-ups

• Build tools/koder-css-audit clamp-floor (referenced in R1.C.3).
• Build tools/koder-overflow-audit for Category A web — runs as Playwright assertion library.
• Extend /k-test to detect surfaces per R4 and stub the suites.