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.
The layering rule ("request-only logic in routes/; scheduler+worker-shared logic
in the plex|downloads|sync packages; cross-cutting primitives as flat core
modules; extract at the SECOND consumer") was real but unwritten — it lived only
in three module docstrings and a one-line README mention. Collect it, plus the
transaction-ownership rule (a mid-operation helper stages, the caller commits),
the atomic-counter / JobStatus-StrEnum conventions, and the one-home-per-config
rule, into backend/app/README.md. Add docs/development.md (run locally + the gate
commands + branching), so a new session/contributor has one place to look instead
of copying whichever pattern they happen to find first.
peter