- MediaLightbox component extracted from dm.tsx. Image now fills a fixed
full-screen box with contentFit=contain instead of an onLoad-computed
aspect ratio, removing the square->real-size jump ("jitter") on open.
- Info-sheet images: render a nested MediaLightbox inside the FormSheet
(stacks above the sheet modal) and track lightboxSource. Removes the
close-sheet-then-reopen workaround that switched context back to the DM.
- Typing indicator: heartbeat (every 2s while focused + non-empty) instead
of keystroke-only sends, so "typing…" holds through thinking pauses;
receiver clear raised to 6s. stop on blur/send/empty.
- Presence: debounce going offline by 12s (online immediate) so brief
presence-sync gaps no longer flicker "Online" <-> "last seen".
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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