fix(screenshot): require full hydrate before skipping prepare scroll

[cursor]

Bug and impact

After #869, a budgeted readiness hydrate on a still-white overflow SPA could mark itself complete after scrolling only one viewport. prepareFullDocument then skipped the long scroll and shipped incomplete fullPage screenshots/PDFs as success for pages that load content lazily on scroll.

Root cause

scrollFullPageToLoadContent set hydrated when hasOverflow && scrolledPx >= viewport, not when the document end was reached. Screenshot/PDF readiness paths pass that flag as scrolled: true into prepareFullDocument.

Fix

Treat a hydrate as complete only when scrolledPx + viewport >= pageHeight (and overflow is present). Partial hydrates still help paint readiness, but prepare runs the full scroll afterward.

Validation

• Added unit coverage for isCompleteScroll and prepare skip/no-skip based on complete vs partial hydrate.
• pnpm exec ava test/prepare-full-document.js test/white-retry.js in packages/screenshot — 10 tests passed.

  

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Note

Medium Risk
Tightens screenshot/PDF full-page scroll completeness, which can change capture timing and output for overflow pages. Logic is localized and covered by unit tests.

Overview
Fixes incomplete fullPage captures on lazy-scroll SPAs. A budgeted hydrate could previously mark itself done after one viewport, so prepareFullDocument skipped the long scroll and returned truncated screenshots/PDFs as success.

hydrated is now true only when overflow exists and scrolledPx + viewport reaches pageHeight. Partial hydrates still help paint readiness, but prepare always runs the full scroll afterward. Adds unit coverage for complete vs partial hydrate skip behavior.

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[coveralls]

Coverage is 80.781% — cursor/critical-bug-management-7c60 into master. No base build found for master.