Let the video tab's Play start at the playhead and reset its button

Two faults in the video tab. A click into the ruler while a clip
played stopped the playback, but the button kept showing "Stop". And
Play always started at the start of the clip, wherever the playhead
stood.

- The tab now reports when the ruler stops the playback, and the
  button switches back to "Play".
- Play starts at the playhead when it lies inside the clip. Without
  a selected clip the whole video counts. Outside or at the end,
  Play starts at the beginning.
- So Stop and Play continue where the playback stopped. A clip that
  ran to its end without loop starts again at the beginning.

Tests: gate on melektaus-atx green. e2e 66 ALL PASSED, 32 checks (2
new in 66e-i). With both fixes taken back, both checks are red with
exactly the reported faults: the button shows "Stop", and Play runs
from 0.71 s, i.e. from the clip start at 0.6 s.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/editor/debug/videoHooks.ts

@@ -28,6 +28,7 @@ export function videoHooks({ state, editor }: HookContext) {
       /** The middle of the clip strip, and of the track under it, at a second of the video. */
       stripAt: (seconds: number) => videoEditor.canvas.stripAt(seconds),
       trackAt: (seconds: number) => videoEditor.canvas.trackAt(seconds),
+      rulerAt: (seconds: number) => videoEditor.canvas.rulerAt(seconds),
       /** The time's zoom, and whether a transition is on its way. */
       zoom: () => videoEditor.canvas.zoomInfo(),
     },

src/editor/video/VideoCanvas.ts

@@ -129,7 +129,7 @@ export class VideoCanvas extends Widget {
   /** The span the player is held to while it plays: the picked clip, else the whole video. */
   private playing: CutSpan | null = null;
   onTogglePlay: () => void = () => {};
-  /** The player stopped by itself (the end of a clip that does not repeat). */
+  /** The player stopped by itself (the end of a clip that does not repeat) or by a click in the ruler. */
   onStopped: () => void = () => {};
 
   constructor(private readonly state: EditorState) {
@@ -202,28 +202,43 @@ export class VideoCanvas extends Widget {
     return this.playing !== null;
   }
 
-  /** Plays the picked clip, else the whole video, from its start, with the video's volume and loop. */
+  /**
+   * Plays the picked clip, else the whole video, with the video's volume and loop: from the
+   * playhead when it stands inside, else from the start.
+   */
   play(): void {
     const asset = this.asset();
     const span = this.shownSpan();
     const element = asset && this.player(asset);
-    if (!asset || !span || !element) return;
+    const preview = this.preview;
+    if (!asset || !span || !element || !preview) return;
     this.playing = span;
     element.muted = false;
     element.volume = videoVolumeOf(asset.props);
     // A moment still wanted from scrubbing would send it back after the start.
-    if (this.preview) this.preview.chase.wanted = null;
-    element.currentTime = span.start;
+    preview.chase.wanted = null;
+    const head = preview.asked;
+    element.currentTime = head >= span.start && head < span.end - LEAST_SPAN ? head : span.start;
     void element.play().catch(() => {});
     this.invalidate();
   }
 
   stop(): void {
+    const preview = this.preview;
+    // The playhead stays where it stopped; the next Play goes on from there.
+    if (this.playing && preview) preview.asked = preview.element.currentTime;
     this.playing = null;
-    this.preview?.element.pause();
+    preview?.element.pause();
     this.invalidate();
   }
 
+  /** Stops from inside the canvas, and tells the header so its button follows. */
+  private halt(): void {
+    if (!this.isPlaying) return;
+    this.stop();
+    this.onStopped();
+  }
+
   /** Where the tab's player stands, in seconds of the video; null while nothing is shown. */
   get playhead(): number | null {
     return this.preview && this.preview.file === this.asset()?.file ? this.preview.element.currentTime : null;
@@ -239,10 +254,7 @@ export class VideoCanvas extends Widget {
       if (videoLoopsOf(asset.props)) {
         element.currentTime = span.start;
         if (element.paused) void element.play().catch(() => {});
-      } else {
-        this.stop();
-        this.onStopped();
-      }
+      } else this.halt();
     }
     this.redraw();
   }
@@ -277,6 +289,15 @@ export class VideoCanvas extends Widget {
     };
   }
 
+  /** The middle of the ruler at a second of the video, on screen (test hook). */
+  rulerAt(seconds: number): Vec2 {
+    const origin = this.getGlobalPosition();
+    return {
+      x: origin.x + secondsToX(this.view, seconds),
+      y: origin.y + this.timelineTop + RULER_HEIGHT / 2,
+    };
+  }
+
   /** The middle of the track at a second of the video, on screen (test hook). */
   trackAt(seconds: number): Vec2 {
     const origin = this.getGlobalPosition();
@@ -418,7 +439,7 @@ export class VideoCanvas extends Widget {
     const from = Math.max(0, Math.min(asset.duration, xToSeconds(this.view, p.x)));
     if (y < RULER_HEIGHT) {
       this.gesture = { kind: 'seek' };
-      this.stop();
+      this.halt();
       this.seekTo(from);
       return;
     }

src/editor/video/VideoEditor.ts

@@ -24,7 +24,7 @@ export class VideoEditor extends AssetTabEditor<VideoAsset, VideoCanvas> {
     this.playButton = new Button('Play', {
       icon: TOOLBAR_ICON_SVG.play,
       minWidth: 72,
-      tooltip: 'Play the picked clip, else the whole video (Space)',
+      tooltip: 'Play the picked clip, else the whole video, from the playhead (Space)',
       onClick: () => this.togglePlay(),
     });
     this.downloadButton = new Button('Download', {