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

frontend/src/components/PlayerModal.tsx

@@ -35,7 +35,7 @@ import {
 } from "../lib/format";
 import { renderDescription } from "../lib/descriptionLinks";
 import { useBackToClose } from "../lib/history";
-import { LS, useAccountPersistedObject } from "../lib/storage";
+import { LS, useAccountPersistedObject, writeAccount } from "../lib/storage";
 import { useScrollFade } from "../lib/useScrollFade";
 
 // Experiment (branch experiment/inline-player): play the video in-app via the
@@ -176,6 +176,9 @@ export default function PlayerModal({
   // while the iframe itself sees mouse movement, so an armed overlay kept the bar — and with it
   // the native fullscreen button — permanently hidden after pressing F.
   const [isFullscreen, setIsFullscreen] = useState(false);
+  // Mirrored into a ref because the keydown handler is bound once (deps: [onClose]) and would
+  // otherwise read `false` forever — the house pattern here (see navRef/volumeRef).
+  const isFullscreenRef = useRef(false);
   // Volume survives the modal, the next video and a reload: a YT.Player is created per video and
   // always starts at full volume. Per-account, like the Plex player's prefs. Level 0 IS the muted
   // state (that's how YouTube's own control behaves), so there's no separate `muted` flag to
@@ -217,6 +220,11 @@ export default function PlayerModal({
   const persistVolume = () => {
     window.clearTimeout(volSaveTimerRef.current);
     volSaveTimerRef.current = undefined;
+    // Write STRAIGHT to storage, not through patchPlayerPrefs: that helper persists inside a
+    // `setState` updater, and React is under no obligation to run an updater for a component that
+    // is unmounting — which is exactly when the flush below fires (close the player right after a
+    // wheel spin). The state copy is only needed while mounted, so patch that separately.
+    writeAccount(LS.ytPlayerPrefs, { volume: volumeRef.current });
     patchPlayerPrefs({ volume: volumeRef.current });
   };
   const applyVolume = (level: number, flash = true) => {
@@ -468,9 +476,10 @@ export default function PlayerModal({
         // fullscreen, where the wheel goes to YouTube's own iframe. But the modal card scrolls
         // (a long description) and Up/Down is how you scroll it from the keyboard — so defer
         // whenever the focused element can still scroll that way, exactly like Space defers to a
-        // focused button.
+        // focused button. NOT in fullscreen though: the card is off-screen there, so deferring
+        // would scroll something invisible and leave fullscreen with no volume control at all.
         const up = e.key === "ArrowUp";
-        if (typing || canScrollBy(el, up ? -1 : 1)) return;
+        if (typing || (!isFullscreenRef.current && canScrollBy(el, up ? -1 : 1))) return;
         e.preventDefault();
         nudgeVolume(up ? 5 : -5);
       } else if (e.key === "ArrowLeft" || e.key === "ArrowRight") {
@@ -524,10 +533,11 @@ export default function PlayerModal({
 
   // Track whether we're the fullscreen element (F, our button, or the browser's own Esc exit).
   useEffect(() => {
-    const onChange = () =>
-      setIsFullscreen(
-        !!document.fullscreenElement && document.fullscreenElement === stageRef.current,
-      );
+    const onChange = () => {
+      const ours = !!document.fullscreenElement && document.fullscreenElement === stageRef.current;
+      isFullscreenRef.current = ours; // read by the once-bound keydown handler
+      setIsFullscreen(ours); // drives the overlay's pointer-events
+    };
     document.addEventListener("fullscreenchange", onChange);
     return () => document.removeEventListener("fullscreenchange", onChange);
   }, []);