Highlighting recurring text (e.g. main-character names) as global
annotations made page turning very laggy. The `progress` effect
re-fans-out every global annotation across every rendered section on
EVERY page turn, and each pass re-walks the section DOM, recomputes
`view.getCFI()` for every occurrence, and tears down + recreates an SVG
overlay per match. The overlays already exist after the first pass, so
this is pure wasted work — profiled at ~25–45ms of synchronous
main-thread time per page turn for 6 names / 226 occurrences across 2
rendered chapters, multiplied on slower mobile hardware.
Memoize, per live section `Document`, which global notes have been
expanded (signature embeds `updatedAt`/style/color/text). Subsequent
page turns short-circuit to ~0ms. Keying on the `Document` makes
invalidation automatic: a re-rendered section gets a fresh document (and
fresh overlayer) so its overlays are rebuilt, while edits/recolors bump
`updatedAt` and toggling global off clears the memo.
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Huang Xin
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