fix(r5): address the second /code-review high round — 7 findings

- the volume keys no longer defer to a scrollable card while in fullscreen
  (mirrored into a ref: the keydown handler is bound once and state would be stale)
- the debounced volume flush writes straight to storage; persisting inside a
  setState updater is not guaranteed to run for an unmounting component
- the HLS sweep also matches the original {key}_{start} directory naming, which
  is what the oldest leftovers on disk actually use
- run_rss_poll returns {new, failed} so an egress outage stops rendering as
  "ok — 0" in the scheduler card and the audit log; /api/sync/rss reports it too
- drop the unused poll_rss_channel (it silently gained a new exception)
- _Breaker.run is generic, so a call site keeps its item-id type
- test helper instead of the generator-throw idiom

backend/app/plex/stream.py

@@ -34,11 +34,13 @@ log = logging.getLogger("siftlode.plex")
 _HLS_ROOT = Path(settings.plex_hls_dir) if settings.plex_hls_dir else Path(settings.download_root) / ".plex-hls"
 _SEG_SECONDS = 6
 _SESSION_IDLE_S = 600  # reap a session with no access for this long
-# A session directory is named `{rating_key}_{int(start_s)}_{tag}_{aoff:+.2f}` (see start_session).
-# `sweep_orphans` deletes ONLY names matching this shape: `_HLS_ROOT` is admin-configurable
+# A session directory is named `{rating_key}_{int(start_s)}_{tag}_{aoff:+.2f}` (see start_session);
+# before multi-audio it was just `{rating_key}_{int(start_s)}`, so the tail is OPTIONAL here — the
+# oldest leftovers on disk carry the old shape and are exactly what the sweep exists to remove.
+# `sweep_orphans` deletes ONLY names matching this: `_HLS_ROOT` is admin-configurable
 # (PLEX_HLS_DIR), so it may legitimately point at a shared scratch path we do not own — a blanket
 # "delete every directory under the root" would take the neighbours with it.
-_SESSION_DIR_RE = re.compile(r"^.+_\d+_[^_]+_[+-]\d+\.\d{2}$")
+_SESSION_DIR_RE = re.compile(r"^.+_\d+(_[^_]+_[+-]\d+\.\d{2})?$")
 
 _lock = threading.Lock()
 _sessions: dict[str, "HlsSession"] = {}