修复视频收藏/聊天记录缩略图恒为破损图片、时长换算错误

MediaThumb 把视频实体自身字节（.val/.ref，给 <video> 解码用）当图片
塞进 <img src>，浏览器无法解码，缩略图恒为损坏图标；改用后端已下发但
从未使用的 .preview/.premime 海报字段（lib/formatters.js 的
quoteImageOrVideo()/inlineVideoAttr() 早已用同一约定）。

时长换算：收藏页把毫秒当秒数传给 secondsToTime，2.4秒视频显示
"39:26"；History 媒体宫格则完全没接上 duration 字段（mediaMessagePayload
是扁平结构，需要跟 history-files 一样重建 Drafty 实体才能取到）。

第十轮最小粒度测试 Ch7 发现（纠正第九轮"证据不足"的结论）。已用真实
收藏视频实测确认：缩略图正确解码（320x240/96x96），时长正确显示 0:02。

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/views/content-library-view.jsx

@@ -91,6 +91,14 @@ function resolveAttachmentUrl(att) {
   if (direct.startsWith('blob:') || direct.startsWith('data:')) return Promise.resolve(direct);
   return getFileUrl(direct.slice(direct.lastIndexOf('/') + 1)).catch(() => null);
 }
+// A video entity's .val/.ref (what resolveAttachmentUrl above resolves) is the video's own bytes --
+// meant for a real <video> element, not decodable by a plain <img>. The poster frame lives in the
+// separate .preview/.premime fields the backend already sends alongside it, same convention
+// lib/formatters.js's quoteImageOrVideo()/inlineVideoAttr() rely on for the chat-bubble quote case.
+function videoPosterUrl(att) {
+  if (!att || !att.preview) return null;
+  return 'data:' + (att.premime || 'image/jpeg') + ';base64,' + att.preview;
+}
 // searchTopicMessages/getTopicMedia results spread the original Drafty content's own fields directly
 // onto each item (mediaMessagePayload/messageSearchPayload flatten `content`, they don't nest it) --
 // reconstruct the Drafty shape from whatever ent/fmt/txt survived so the same attachment-extraction
@@ -165,13 +173,18 @@ function LinkText({url, onOpen, removed}) {
   return <button type="button" className="library-link-text" onClick={() => onOpen && onOpen(url)}><Icon>link</Icon><span>{url}</span></button>;
 }
 
-function MediaThumb({url, video, duration, onOpen, removed}) {
+function MediaThumb({url, poster, video, duration, onOpen, removed}) {
   if (removed) {
     return <div className="library-media-thumb removed"><Icon>{video ? 'videocam_off' : 'broken_image'}</Icon><em>{video ? '视频已失效' : '图片已失效'}</em></div>;
   }
+  // video's own bytes (url) can't be decoded by <img> -- only the poster frame can. Images have no
+  // separate poster; their own url doubles as the thumbnail.
+  const imgSrc = video ? poster : url;
   return <button type="button" className="library-media-thumb" onClick={onOpen}>
-    {url ? <img src={url} alt={video ? '视频缩略图' : '图片缩略图'} /> : <Icon>{video ? 'videocam' : 'image'}</Icon>}
-    {video ? <><Icon>play_circle</Icon>{duration ? <small>{secondsToTime(duration)}</small> : null}</> : null}
+    {imgSrc ? <img src={imgSrc} alt={video ? '视频缩略图' : '图片缩略图'} /> : <Icon>{video ? 'videocam' : 'image'}</Icon>}
+    {/* duration follows the AU/VD entity storage convention of milliseconds (see sendVideoAttachment/
+        insertVideo), same conversion widgets/audio-player.jsx already does for its own duration prop. */}
+    {video ? <><Icon>play_circle</Icon>{duration > 0 ? <small>{secondsToTime(duration / 1000)}</small> : null}</> : null}
   </button>;
 }
 
@@ -192,7 +205,8 @@ function FavoriteItem({item, onOpen, selecting, selected, onSelect}) {
       {item.type === 'voice' ? <VoiceCard att={att} head={item.snapshot && item.snapshot.head} removed={item.availability === 'removed'} /> : null}
       {item.type === 'link' ? <LinkText url={(item.snapshot && item.snapshot.content && item.snapshot.content.url) || plainTextOf(item.snapshot && item.snapshot.content, item.snapshot && item.snapshot.text)}
         onOpen={onOpen} removed={item.availability === 'removed'} /> : null}
-      {item.type === 'image' || item.type === 'video' ? <MediaThumb url={item._thumbUrl} video={item.type === 'video'} duration={att && att.duration} onOpen={onOpen} removed={item.availability === 'removed'} /> : null}
+      {item.type === 'image' || item.type === 'video' ? <MediaThumb url={item._thumbUrl} poster={item.type === 'video' ? videoPosterUrl(att) : null}
+        video={item.type === 'video'} duration={att && att.duration} onOpen={onOpen} removed={item.availability === 'removed'} /> : null}
       <footer><span>来自 {source}</span><time>{shortDateFormat(new Date(item.collected_at))}</time></footer>
     </div>
   </article>;
@@ -629,8 +643,14 @@ function History({view, hashParams, myUserId, onToast}) {
         <LinkText url={item.url || plainTextOf(item.txt !== undefined ? {txt: item.txt, fmt: item.fmt, ent: item.ent} : undefined, item.text)}
           onOpen={openLink} removed={item.availability === 'removed'} />
       </React.Fragment>)}</section> :
-      <section className="library-media-grid">{list.map(item => <MediaThumb key={item.seq} url={mediaUrls[item.seq]} video={view === 'history-videos'}
-        duration={item.duration} onOpen={() => jump(item.seq)} removed={item.availability === 'removed'} />)}</section>}
+      <section className="library-media-grid">{list.map(item => {
+        // mediaMessagePayload (getTopicMedia) is flat and has no top-level `duration`/poster fields --
+        // the real values live inside the reconstructed Drafty entity, same as history-files' FileCard
+        // already reconstructs `att` for name/size/mime just above.
+        const videoAtt = view === 'history-videos' ? attachmentFromFlat(item) : null;
+        return <MediaThumb key={item.seq} url={mediaUrls[item.seq]} poster={videoAtt ? videoPosterUrl(videoAtt) : null} video={view === 'history-videos'}
+          duration={videoAtt && videoAtt.duration} onOpen={() => jump(item.seq)} removed={item.availability === 'removed'} />;
+      })}</section>}
       {hasMore ? <button type="button" className="library-load-more" onClick={() => load(true)}>加载更多</button> : null}
     </main>
   </div>;