- edit.py: extract _run_ffmpeg_best_effort (one run+timeout+swallow policy shared by
thumbnail_to_jpg / ensure_poster / ensure_storyboard) + a build_thumbnail_jpg_cmd
builder, matching the module's other ffmpeg commands.
- thumbnail_to_jpg: copy an already-JPEG thumbnail (Facebook, and Reddit's jpeg-under-
a-.png-name) instead of re-encoding it; only webp/png-proper are decoded via ffmpeg.
- errors.py: drop the redundant "account authentication" classify marker
("authentication is required" already covers the known Reddit message).
- formats.py: document that the opt-in EmbedThumbnail is unaffected by dropping the
convertor (it converts unsupported thumbs to PNG, not the crashing mjpeg2jpeg path).
- test_titles.py: guard the ReDoS regression with a thread + timeout (deterministic
"must not hang") instead of a wall-clock assertion.