New features:
- Video playback: lightbox renders <video controls autoPlay> for MsgType.Video;
thumbnail tiles show a play-button badge overlay; LightboxImage renamed to
LightboxMedia to handle both types.
- Auto-load on scroll: IntersectionObserver on a sentinel div replaces the
manual "Load More" button. Detaches while loading or when history is exhausted.
- Month separators: image/video grid grouped by month ("June 2026", etc.) with
a hairline divider; separator only shown when more than one month is present.
Bugs fixed by code review:
- flatIdx++: index was incremented before the !thumbMxc null-guard, causing
tiles rendered after a skipped event to open the wrong lightbox item. Guard
is now checked first; flatIdx only increments when a tile actually renders.
- lightboxIndex never reset on tab switch: stale index kept the lightbox open
(or opened the wrong item) after switching tabs. handleTabChange() now calls
setLightboxIndex(null) alongside setTab().
- Silent catch retry storm: pagination errors left canLoadMore=true, causing
the IntersectionObserver to re-fire handleLoadMore on every render cycle
when the sentinel was still visible. Error state now sets loadError=true,
removes the sentinel, and shows a manual Retry button instead.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
jared
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