WORK-433
ID:WORK-433Status:done

reveal IntersectionObserver behaviour + enhancement gating

SPEC-105 §5–§6: the timing trigger and the no-JS/SSR safety. A tiny IntersectionObserver behaviour flips data-in-view; enhancement gating guarantees the static page is always complete. JS = when, CSS = how.

Priority:highComplexity:moderateMilestone:v0.24.0Source:SPEC-105
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Criteria completion

Criteria completion: 3 of 3 (100%) checked; tracking started on Jun 15, no incremental history yet0%25%50%75%100%Jun 15Jun 16

Tracking started Jun 15 — check back for trends.

Relationships

Implements 1
Related 5
Branches 6
main current done
changeset-release/main doneclaude/v024-work431-reveal-facet donemain doneclaude/milestone-v0.24.0-split readyclaude/v023-bg-motion-breakdown readyclaude/defer-work-417 ready

Scope

  • reveal behaviour — joins tabs/accordion/datatable/form in packages/behaviors/src/. Observes each [data-reveal]:not([data-reveal="none"]) container; on first intersection it sets data-in-view and unobserves. Theme-agnostic: one state attribute, nothing else.
  • Reduced-motion path — honour matchMedia('(prefers-reduced-motion: reduce)'): mark everything in-view immediately (belt-and-braces with the global reset).
  • Enhancement gating (cardinal rule) — SSR/no-JS/crawler render the fully visible final state; never bake opacity:0 that only JS removes. The pre-entrance state is scoped under a root data-animate flag the behaviour adds on boot; no flag → every section fully rendered.

Acceptance Criteria

  • An IntersectionObserver reveal behaviour sets data-in-view on first intersection and unobserves; under prefers-reduced-motion it marks all in-view immediately.
  • Enhancement gating: SSR/no-JS/crawler render the fully visible final state (no opacity:0 baked in); the pre-entrance state is scoped under a root data-animate flag the behaviour adds on boot; the WORK-352 reduced-motion reset still neutralises motion.
  • The behaviour is theme-agnostic (sets only data-in-view/the root flag) and frame-agnostic; tests cover the observe→reveal→unobserve cycle, the reduced-motion path, and the no-JS/SSR complete-render guarantee.

Dependencies

  • WORK-431 — observes data-reveal. Pairs with WORK-432 (the gated pre-entrance CSS).

References

  • SPEC-105 §5–§6 · packages/behaviors/src/ (tabs/accordion/datatable/form pattern) · reduced-motion baseline WORK-352 (packages/lumina/styles/global.css).

Resolution

Completed: 2026-06-16

Branch: claude/v024-work431-reveal-facet (continued).

What was done

  • New packages/behaviors/src/behaviors/scroll-reveal.ts — a page-level behaviour (not keyed by data-rune; it scans the data-reveal attribute), registered in initRuneBehaviors alongside scrollspy/copy and exported from the package index.
  • On boot it sets the root data-animate gate (on document.documentElement), then observes each [data-reveal]:not([data-reveal="none"]) with an IntersectionObserver; on first intersection it sets data-in-view and unobserves (one-shot entrance). rootMargin: '0px 0px -10% 0px' so the entrance reads as the container scrolls in.
  • Reduced-motion / no-IO path: marks every container in-view immediately (no observer), reaching the same final state without animation — belt-and-braces with the WORK-352 global reset.
  • Enhancement gating: the pre-entrance hidden CSS is scoped under [data-animate]; with no JS the gate is absent, so SSR/no-JS/crawler render the fully-visible final state — no opacity:0 baked in.
  • Naming: deliberately NOT the existing reveal rune behaviour (disclosure, keyed by data-rune="reveal"); this is scrollRevealBehavior, keyed on the data-reveal attribute.
  • Tests: packages/behaviors/test/scroll-reveal.test.ts (9) — gate-on-boot, no-op without containers, reveal="none" skip, observe→reveal→unobserve, non-intersecting no-op, reduced-motion immediate path, no-IO path, cleanup disconnect, and the SSR/no-JS complete-render guarantee.

Notes

  • Theme- and frame-agnostic: sets only the root flag + data-in-view. JS = when, CSS = how.
  • Verified in a generated Lumina gallery: the inlined behaviour script and motion CSS both ship; pixel-diff runs in CI (chromium can't download in the sandbox).