Deep-review round 4, backend half.
- The periodic HLS reaper (round 3) applied the "finished and unfetched for 30 s" rule that only a
NEW session request may apply. A remux finishes long before the film, and a paused player with a
full buffer fetches nothing, so a one-minute pause killed the session and playback died ~30 s after
resuming. The periodic pass is `reap_abandoned` now (the long idle limit, finished or not).
- A subtitle `publish` that could not keep its output (full / read-only cache volume) returned
quietly, so every poll queued the window and the whole-container pass again. It reports failure
and the pass is backed off like a failed read; a cached VTT that cannot be READ is answered
`unavailable` (`cache_unreadable`) instead of scheduling reads that can never land.
- The subtitle routes bound `rating_key` / `sub_ord` (they become a cache file name: a 250-digit
one was ENAMETOOLONG, which pathlib's exists() re-raises -> a 500), and the cache helpers no longer
throw on such a name.
- One app-wide handler turns psycopg's "text fields cannot contain NUL" DataError into a 422: round 3
guarded only the by-rating_key lookup, and `contains=`, `contains_group=`, reorder/bulk key lists
and the collection search still 500'd.
- The hand-written `db.get(...) is None -> 404 "Unknown ..."` siblings use `get_or_404` with a
`what` (channel / video / user), so the Hungarian UI no longer shows English for a gone row.
peter
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