fix: load videos in Media Gen preview on mobile (muted autoplay + poster)

.changelog/NEXT.md

@@ -17,3 +17,4 @@ TBD
 ## Fixed
 
 - **Chief of Staff pane overflow** — content panel collapses to a single `flex-1 min-h-0 min-w-0 overflow-y-auto overflow-x-hidden` div so tall tab content scrolls inside the panel instead of expanding it. Event log rows in both `EventLog` and `TerminalCoSPanel` get `break-all` so long unbreakable tokens (URLs, hashes, paths) wrap inside the 320px sidebar instead of pushing the column wider visually.
+- **Videos now load in the Media Gen preview on mobile.** Both the preview-modal (lightbox) `<video>` and the Video Gen page's inline result preview autoplayed unmuted, which iOS/Android block outside a direct user gesture — so the clip never started and the area showed only black ("not loading"). They now play `muted` (autoplay-eligible everywhere; controls let you unmute) and render the thumbnail as a `poster`, so the frame is visible immediately even while the clip buffers.

client/src/components/media/MediaLightbox.jsx

@@ -226,10 +226,28 @@ export default function MediaLightbox({
           onTouchEnd={onTouchEnd}
         >
           {isVideo ? (
-            /* playsInline keeps iOS Safari from auto-promoting autoplay video
-               to a native fullscreen player — exiting that leaves the modal
-               laid out as a tiny strip with no reachable close button. */
-            <video src={item.downloadUrl} controls autoPlay loop playsInline className={imgMax} />
+            /* Mobile playback contract:
+               - playsInline keeps iOS Safari from auto-promoting autoplay video
+                 to a native fullscreen player — exiting that leaves the modal
+                 laid out as a tiny strip with no reachable close button.
+               - muted is required for autoplay under the mobile media-engagement
+                 policy: iOS/Android block unmuted autoplay that isn't fired from
+                 a direct user gesture, so without it the clip never starts and the
+                 area just shows black ("not loading"). Controls let the user unmute.
+               - poster paints the thumbnail immediately so there's no blank box
+                 while the clip buffers (and a visible frame even if playback is
+                 deferred). previewUrl is the video's thumbnail; omit when absent. */
+            <video
+              src={item.downloadUrl}
+              poster={item.previewUrl || undefined}
+              controls
+              autoPlay
+              loop
+              muted
+              playsInline
+              preload="metadata"
+              className={imgMax}
+            />
           ) : (
             <MediaImage src={item.previewUrl} alt={item.prompt} className={`${imgMax} object-contain`} placeholderClassName="w-full h-full" />
           )}

client/src/components/media/MediaLightbox.test.jsx

@@ -0,0 +1,48 @@
+import { describe, it, expect, vi } from 'vitest';
+import { render } from '@testing-library/react';
+import MediaLightbox from './MediaLightbox';
+
+// The footer's AddToCollectionMenu and the (closed) PromptRefineModal pull the
+// whole API surface (and useProviderModels) into the import graph. Neither is
+// under test here, so stub them to inert nodes — that keeps the test focused
+// on MediaLightbox's own <video> markup and off the network.
+vi.mock('./AddToCollectionMenu', () => ({ default: () => null }));
+vi.mock('./PromptRefineModal', () => ({ default: () => null }));
+
+const videoItem = {
+  kind: 'video',
+  key: 'video:abc',
+  id: 'abc',
+  filename: 'abc.mp4',
+  previewUrl: '/data/video-thumbnails/abc.jpg',
+  downloadUrl: '/data/videos/abc.mp4',
+  prompt: 'a cat',
+  createdAt: Date.now(),
+};
+
+describe('MediaLightbox video element (mobile playback)', () => {
+  it('renders the <video> with a poster + muted + playsInline so it loads/autoplays on mobile', () => {
+    const { container } = render(<MediaLightbox item={videoItem} onClose={() => {}} />);
+    const video = container.querySelector('video');
+    expect(video).toBeTruthy();
+    // src points at the full asset
+    expect(video.getAttribute('src')).toBe('/data/videos/abc.mp4');
+    // poster = thumbnail so a blank box never shows while the clip buffers,
+    // and the frame is visible even if mobile autoplay is deferred.
+    expect(video.getAttribute('poster')).toBe('/data/video-thumbnails/abc.jpg');
+    // muted is required for autoplay under mobile media-engagement policy.
+    expect(video.muted).toBe(true);
+    // playsInline keeps iOS from promoting to a native fullscreen player.
+    expect(video.hasAttribute('playsinline')).toBe(true);
+    expect(video.hasAttribute('loop')).toBe(true);
+    expect(video.hasAttribute('controls')).toBe(true);
+  });
+
+  it('omits poster when the video has no thumbnail rather than rendering an empty poster', () => {
+    const { container } = render(
+      <MediaLightbox item={{ ...videoItem, previewUrl: null }} onClose={() => {}} />
+    );
+    const video = container.querySelector('video');
+    expect(video.hasAttribute('poster')).toBe(false);
+  });
+});

client/src/pages/VideoGen.jsx

@@ -1384,7 +1384,21 @@ export default function VideoGen() {
           </div>
           <div className="aspect-video max-w-[420px] mx-auto bg-port-bg border border-port-border rounded-lg overflow-hidden flex items-center justify-center relative">
             {result ? (
-              <video src={result.path || `/data/videos/${result.filename}`} controls autoPlay loop playsInline preload="metadata" className="w-full h-full" />
+              // muted so the clip autoplays under the mobile media-engagement
+              // policy (iOS/Android block unmuted autoplay outside a user
+              // gesture — otherwise it just shows black); poster paints the
+              // thumbnail while it buffers. Controls let the user unmute.
+              <video
+                src={result.path || `/data/videos/${result.filename}`}
+                poster={result.thumbnail ? `/data/video-thumbnails/${result.thumbnail}` : undefined}
+                controls
+                autoPlay
+                loop
+                muted
+                playsInline
+                preload="metadata"
+                className="w-full h-full"
+              />
             ) : generating ? (
               <div className="text-gray-500 text-xs flex flex-col items-center gap-1.5">
                 <BrailleSpinner />