Two findings from JohnBaumb on the engine refactor.
(1) Every download client returned None when self._engine was None,
just logging an error. The orchestrator's download_with_fallback
treated None as "source declined", so the user got no feedback —
download silently disappeared. Now each client raises a RuntimeError
on the engine-not-wired path. download_with_fallback already catches
plugin exceptions, logs a warning, and tries the next source — so
the visible behavior is "real error in logs + fallback to next
source" instead of "silent drop". Six clients touched (deezer, hifi,
qobuz, soundcloud, tidal, youtube). Pinning tests updated to expect
raise.
(2) Monitor's engine.get_all_downloads() walked every plugin
including soulseek, but the same monitor loop already pulled slskd
transfers via the transfers/downloads endpoint a few lines earlier —
soulseek's records were being fetched twice per tick. Same issue in
web_server.py's get_cached_transfer_data path. Added an exclude
parameter to engine.get_all_downloads(); both call sites now pass
('soulseek',). New test pins the exclude semantic.
Also fixed a stray 8-space over-indent on the for-loop body in
get_cached_transfer_data (cosmetic, JohnBaumb flagged the same
pattern in monitor.py earlier).
Same migration pattern as C2-C5. Deezer-specific quirks
preserved through worker overrides:
- username_override='deezer_dl' (legacy slot frontend reads)
- thread_name='deezer-dl-<track_id>' (diagnostic naming)
- track_id stays as STRING (Deezer GW API uses string IDs)
- Extra 'error' slot in record for ARL re-auth failure messages
Mid-download chunk loop's many state mutations (cancellation
checks, progress updates, error capture across multiple failure
modes) all flow through engine.update_record / get_record now.
Added _set_error and _is_cancelled helpers to keep call sites
readable.
Pinning tests updated. Suite still green (319 download tests).
6 tests pin the Deezer contract:
- track_id stays as STRING (Deezer GW API uses string IDs).
- username slot is the legacy `'deezer_dl'` (frontend depends on it).
- Auth gate at top of `download()` returns None BEFORE thread spawn.
- Defensive fallback: filename without `||` synthesizes display name.
- Thread is named `deezer-dl-<track_id>` for diagnostics.
- State dict has Deezer-specific `error` slot.
