Round-1 review fixes on the E3 branch:
- prune partial-fetch (correctness): `_paginate` now reports whether it reached
the server's reported `total`; `_prune_stale` prunes only on a COMPLETE
non-empty listing. A truncated fetch (a mid-sequence empty/short page before
total — a transient Plex hiccup) no longer deletes the rows it merely failed
to list. New test: a listing that claims 5 but returns 1 prunes nothing.
- `_prune_stale` (robustness): `stats.get("pruned", 0) + 1` — no KeyError when a
caller's stats dict omits the key.
- service transitions (conventions): pause/resume/redownload use the JobStatus
StrEnum instead of loose "queued"/"paused"/"error" literals, matching cancel.
- ffmpeg progress writer (correctness): a stuck-percent heartbeat now runs on its
OWN 1/interval budget, so it can't consume the progress-write slot and delay a
real percent change by up to an interval.
- backend/app/README.md (conventions): reword the transaction-ownership rule to
quote and extend CLAUDE.md's canonical ("handler/job-wrapper commits; helpers
flush; only quota owns its session") instead of stating a contradicting
"helpers MAY commit" carve-out.
ruff clean, full DB-lane 364 pass.
A sync was upsert-only: a movie/show/season/episode removed from Plex stayed
browsable forever and 404'd on playback. Each section now diffs the rating_keys
it just listed against the stored ones and deletes the stale rows (watch-state /
playlist links cascade via the existing FKs), mirroring the collections prune
that already shipped.
Safety: the prune is GUARDED on a non-empty listing (_prune_stale returns early
when `seen` is empty), so a transient Plex glitch that yields an empty page can
never mass-delete a library — the metadata is cheap to re-sync, an accidental
wipe is the only real risk. Shows prune leaf-first (episodes -> seasons -> shows)
so a stale row is deleted directly before its parent's cascade reaches it.
Out of scope (separate follow-up): library-level reconcile of a whole removed
section + retiring the dead `PlexLibrary.enabled` column.
Tests: movie prune + watch-state cascade, the empty-listing guard (mutation-
verified — removing the guard wipes everything), show/season/episode prune.
351 DB-lane pass, ruff clean.
peter