- Throttled write inside the scroll rAF tick (every 200ms during active
scroll) captures mid-page ratio changes. Previously only page-boundary
crossings triggered writes, so refreshing mid-page restored to top of
that page instead of exact position.
- pagehide + visibilitychange + unmount flush captures the final 0-200ms
before tab close / bfcache / nav.
- hasScrolledRef guards writes so opening a chapter without scrolling
doesn't clobber a prior deep-progress bookmark for a different chapter.
- getBoundingClientRect replaces offsetTop/offsetHeight for subpixel
precision and positioning-ancestor independence.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
yiekheng
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