The prior test guarded a verbatim MIRROR of the two scroll-restore useLayoutEffect
blocks — the reviewer proved removing '&& editor' from the real page-editor.tsx left
the test green (a copy, not the original). Extract the wiring into an exported
useScrollRestoreOnSwap(pageId, editor, showStatic) hook (the two effects verbatim +
useScrollPosition inside; F1 budget logic untouched), call it once from page-editor.tsx
(replacing the removed useScrollPosition call + both effects), and rewrite the test to
render the REAL hook — deleting the mirror and the false 'regresses in lockstep' comment
(F2-doc). Non-vacuity proven: removing '&& editor' from the real hook reddens the guard
test.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
F1: pin the shared restoreStartRef timeout budget — re-triggers share ONE budget
(measured from the first call), not a per-trigger restart. Test drives short content
(polls), triggers at t=0 and t=3s, and asserts the clamp fires at t=5s from the FIRST
call. Verified non-vacuous: a mutant that resets the budget on each trigger fails it.
F2: cover the two useLayoutEffect scroll-restore blocks. A full PageEditor mount has
no precedent in the client suite (it builds live Hocuspocus/IndexedDB providers +
collab tiptap; the static->live swap gates on isCollabSynced, only reproducible by
driving mocked provider callbacks = testing the mocks). Per the reviewer's allowance
for a justified lighter variant: page-editor.test.tsx reproduces the two effects and
(1) asserts the [showStatic, editor] deps + the '&& editor' guard via a stable spy,
(2) drives the REAL useScrollPosition end-to-end so the post-swap re-assert is the
sole cause of scrollTo.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
The reading-position restore fired only after collab sync (`!showStatic`),
so the page painted at the top and then visibly jumped — and readers who had
already started scrolling were rudely yanked back to the saved position.
- Abort restore permanently on genuine user scroll intent: `wheel`/`touchstart`
unconditionally, and `keydown` only for real scroll keys (Arrow/Page/Home/End/
Space) so shortcuts and typing do not disable it. Our own `window.scrollTo`
never emits these, so restore cannot self-abort.
- Restore earlier via `useLayoutEffect` (before paint) while the static/cached
content is laid out, and re-assert once after the static->live editor swap.
- Make `restoreScrollPosition` idempotent with a redundancy guard so the two
triggers never double-scroll; share one bounded timeout budget across them.
- Add tests for interaction-abort, scroll-key filtering, idempotence.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
agent_coder
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