Replace radius-based sliding window with fixed 5-page chunks. On entering
a chapter, fetch pages [current..current+4]. When user approaches within
3 pages of either the cached range's high or low edge, fetch the next
forward or backward chunk. Near chapter end, also prefetch the next
chapter's first chunk so the hand-off is seamless.
Pruning now also keeps chapter+1 when user is in the last
KEEP_PREV_CHAPTER_PAGES of current chapter — previously scrolling back
from a just-entered chapter would prune it immediately even though the
next forward scroll would re-fetch it.
Also disable window.history.scrollRestoration on reader mount. On
refresh while in an auto-appended chapter, the stored scrollY
references a taller document than reloads with only the URL chapter —
browser would clamp and land near the bottom. Manual mode lets the
useLayoutEffect resume logic be the source of truth.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
yiekheng
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