humanspeak / svelte-virtual-list / 29354161321

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feat(virtual-list): public onRangeChange callback for visible-range state (#424)

* feat(virtual-list): add public onRangeChange callback

Promote the already-computed visible range and at-top/at-bottom state to a
first-class, documented onRangeChange prop. Previously this information was
only reachable through debugFunction (gated behind debug=true with console
noise). The new callback delivers a trimmed { start, end, atTop, atBottom }
payload for impression tracking, URL sync, and scroll-position persistence.

- Add SvelteVirtualListRangeInfo type and onRangeChange prop (types.ts)
- Export the new type from index.ts
- Fire the callback from a deduped $effect mirroring the debug effect's
  shape; atTop/atBottom math matches createDebugInfo so the two channels
  cannot disagree
- Unit tests: initial fire, dedupe, payload shape, absent-prop safety
- E2E fixture + spec at /tests/other/range-callback (house stats ritual)
- README props row + usage snippet

debugFunction / SvelteVirtualListDebugInfo are unchanged.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

* test(virtual-list): make range-callback fixture self-judging (red/green)

Bring the fixture up to the house "loud and diagnostic" standard set by the
issue-416 page — previously a broken callback would read as "pending"
forever and the list backdrop was neutral gray.

- Capture the FIRST delivered payload separately from the latest one
- Add two red/green verdict rows in the house pass/fail style:
  stat-initial (first payload start=0 atTop=1) and stat-final (latest
  payload atBottom=1 end=ITEM_COUNT after the probe)
- Verdicts resolve to pass OR fail once the probe completes — zero
  deliveries (and even a missing viewport) judge as fail, never pending
- Solid warning-red #ffc2c2 list backdrop so unrendered viewport is visible
- stat-range line format kept byte-compatible with the existing spec
- Spec: new test asserting the page's own verdicts (waits require a digit)

Co-Authored-By: ... (continued)

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