Root cause: the steady-state loop (#vid-loop) restarts only via a narrow
timeupdate window (last 0.08s -> seek to LOOP_TAIL_S), with native loop off.
Headless Chromium reliably lands a final timeupdate in that window, but under
real-browser decode/GPU load a timeupdate can skip past it; the clip then fires
'ended' and freezes on its last frame ('videos aren't looping'). There was no
recovery path. Add an 'ended' listener that seeks back to the tail and resumes,
guaranteeing the loop regardless of the timeupdate race. No change to normal
playback. Proven by a Playwright regression test that forces the ended state.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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