fix(video): 全屏关闭后内嵌进度条跳变而非从0扫动

程序化 seek 同步全屏播放进度时,新增 snapProgress 抑制进度条
的宽度过渡动画,使其直接落到观看位置,恢复播放时再启用过渡。

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

src/components/messageStream/MessageInlineVideo.tsx

@@ -120,13 +120,22 @@ export function MessageInlineVideo({
   const [currentTime, setCurrentTime] = useState(initialTime);
   const [duration, setDuration] = useState(attachment.durationSec ?? 0);
   const [isScrubbing, setIsScrubbing] = useState(false);
+  // When we programmatically seek (e.g. syncing the playhead back from the
+  // fullscreen overlay) the progress fill should jump straight to the watched
+  // position instead of sweeping up from its old width via the CSS transition.
+  // Cleared as soon as real playback resumes so live progress stays smooth.
+  const [snapProgress, setSnapProgress] = useState(false);
 
   const t = TOKENS[size];
 
   useEffect(() => {
     const v = videoRef.current;
     if (!v) return;
-    const onPlay = () => setIsPlaying(true);
+    const onPlay = () => {
+      setIsPlaying(true);
+      // Real playback advances the fill smoothly again; re-enable transitions.
+      setSnapProgress(false);
+    };
     const onPause = () => setIsPlaying(false);
     const onTime = () => {
       setCurrentTime(v.currentTime);
@@ -232,7 +241,9 @@ export function MessageInlineVideo({
           // Update React state synchronously so the progress bar paints the
           // new playhead in the next frame, before the <video> seek round-
           // trip emits its own events (paused videos don't fire timeupdate
-          // and `seeked` can lag ~hundreds of ms).
+          // and `seeked` can lag ~hundreds of ms). Snap the fill to the new
+          // position so it doesn't sweep up from its pre-fullscreen width.
+          setSnapProgress(true);
           setCurrentTime(finalTime);
           onTimeUpdate?.(finalTime);
           const apply = () => {
@@ -334,7 +345,9 @@ export function MessageInlineVideo({
           >
             <div
               className={`h-full bg-white ${
-                isScrubbing ? "" : "transition-[width] duration-150 ease-out"
+                isScrubbing || snapProgress
+                  ? ""
+                  : "transition-[width] duration-150 ease-out"
               }`}
               style={{ width: `${progressPct}%` }}
             />