fix(ui): scrubber drag listener leak and caption boundary

Scrubber attached pointermove/pointerup to window on drag start but
only removed them on pointerup. If the component unmounted mid-drag
(e.g. compact <-> desktop layout swap remounts a different Scrubber),
the listeners outlived it and kept calling actions.seek. Track the
active drag cleanup in a ref and run it on unmount; also release on
pointercancel for touch.

Caption fallback scan treated a cue as active at exactly its end time
(now <= endTime). The HTML active-cue rule is start <= now < end, so
the ending cue could briefly stack with the next one. Use strict <.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: karngyan

src/ui/scrubber.tsx

@@ -20,6 +20,10 @@ export function Scrubber() {
 
   const trackRef = useRef<HTMLDivElement | null>(null)
   const previewRef = useRef<HTMLDivElement | null>(null)
+  // Cleanup for an in-flight drag, so window listeners don't outlive the
+  // component if it unmounts mid-drag (e.g. layout swaps compact <-> desktop).
+  const dragCleanup = useRef<(() => void) | null>(null)
+  useEffect(() => () => dragCleanup.current?.(), [])
   const [hover, setHover] = useState<{ x: number; time: number } | null>(null)
   const [sb, setSb] = useState<Storyboard | null>(null)
   // measured (post-transform) preview width + track width, to keep the preview
@@ -55,9 +59,13 @@ export function Scrubber() {
     const up = () => {
       window.removeEventListener("pointermove", move)
       window.removeEventListener("pointerup", up)
+      window.removeEventListener("pointercancel", up)
+      dragCleanup.current = null
     }
+    dragCleanup.current = up
     window.addEventListener("pointermove", move)
     window.addEventListener("pointerup", up)
+    window.addEventListener("pointercancel", up)
   }
 
   const onPointerMove = (e: ReactPointerEvent<HTMLDivElement>) => {

src/util/captions.ts

@@ -34,7 +34,7 @@ export function activeCueText(
       const hits: TextTrackCue[] = []
       for (let j = 0; j < all.length; j++) {
         const c = all[j]
-        if (c && c.startTime <= now && now <= c.endTime) hits.push(c)
+        if (c && c.startTime <= now && now < c.endTime) hits.push(c)
       }
       const text = joinCues(hits)
       if (text) return text