Pinning gaps he flagged after his second pass:
- register_plugin when set_engine() raises: registration must succeed
+ plugin stays in the registry (download() raises later, surfacing
the error to the user via download_with_fallback). Pin so a future
refactor can't accidentally propagate the set_engine exception and
crash boot.
- engine.get_all_downloads exclude actually doesn't invoke the plugin:
ID-only check would pass even if soulseek's get_all was called and
returned []; sentinel proves the plugin isn't touched at all.
- Cancel mid-flight observable from inside _download_sync: existing
tests pin Cancelled-preserve AFTER impl returns, this pins the
contract plugins rely on (engine.get_record reflecting Cancelled
state during the impl thread's polling loop).
- configured_clients() with broken is_configured(): the try/except
guard exists but had no test — broken plugin is silently skipped,
healthy ones still surface.
- Per-source delay independence: YouTube's 3s rate-limit delay must
not block a Tidal download starting in parallel. Companion to the
per-source-locks test.
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