- ExtractSubtitlesVTTMulti: distrust output when ffmpeg is killed by signal
(45-min timeout on a too-big remux) — a truncated WebVTT passed the len>0
check and got cached as a silently-incomplete track until the media mtime
changed. Skip all output on signal-kill; keep it on a clean non-zero exit.
- stream handlers: read the sidecar cache BEFORE the ffmpegPath guard so a
pre-warmed sub/thumbnail still serves if ffmpeg was removed after the cache
was filled.
- scan: log when the prewarm is skipped because ffmpeg is unavailable (matches
the daemon; CLAUDE.md wants bootstrap to log on every branch).
- unexport sidecarDir/subtitleCachePath/thumbnailCachePath (no external callers).
- prewarm: surface a sample error in the summary so a systemic ffmpeg failure
is distinguishable from one corrupt file.
- add unit tests: codec whitelist, cache paths, mtime freshness, atomic write,
thumb-position dedup.
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