e2e/specs/phone-progress-line.spec.ts

@@ -79,6 +79,20 @@ test.describe('the progress line sits on the border between the bars', () => {
     await play(app);
   });
 
+  /*
+   * Every test here starts a LONG_TRACK and the suite is workers: 1,
+   * fullyParallel: false against one long-lived app — so without this
+   * the four phone-* specs that follow alphabetically inherit a playing
+   * queue. phone-transport.spec.ts records where that lesson came from:
+   * the fault first showed up as a flake in a spec about something else.
+   */
+  test.afterEach(async ({ app }) => {
+    await callBinding(app, 'queue.Queue.Clear').catch(() => {
+      /* already empty */
+    });
+    await app.setViewportSize(DESKTOP);
+  });
+
   test('spans the width, between the mini player and the tab bar', async ({
     app,
   }) => {

frontend/test/components/progress-line.test.ts

@@ -7,8 +7,8 @@
  * backend reported rather than a count of its own, and that it is
  * neither announced nor touchable. It cannot see where it sits — that
  * is the shell's grid, and it is asserted in
- * `e2e/specs/phone-transport.spec.ts` where there is a real bar with a
- * real tab bar under it.
+ * `e2e/specs/phone-progress-line.spec.ts` where there is a real bar
+ * with a real tab bar under it.
  */
 import { describe, expect, it, beforeEach, afterEach, vi } from 'vitest';
 
@@ -168,6 +168,36 @@ describe('<player-progress-line>', () => {
         expect(scale(el)).toBeCloseTo(41 / 90, 3);
     });
 
+    /*
+     * The reason this component asks `matchMedia` instead of letting a
+     * stylesheet hide it: a media query cannot stop a 1 Hz interval
+     * running for the life of every desktop session. That claim is
+     * load-bearing in CLAUDE.md, so it is asserted rather than
+     * described — the timer count, because a desktop render is empty
+     * either way and so cannot tell the two apart.
+     */
+    it('runs no interpolation timer above the breakpoint', async () => {
+        pretendPhone(false);
+        vi.useFakeTimers();
+
+        const el = await fixture('player-progress-line');
+
+        emit(Events.TrackChanged, { ...TRACK, trackChangeId: 9 });
+        emit(Events.PlaybackStateChanged, { state: 'playing' });
+        emit(Events.PlaybackPositionChanged, {
+            positionSeconds: 3,
+            trackLength: 90,
+            trackChangeId: 9,
+            seq: 9,
+            playing: true,
+        });
+        await vi.advanceTimersByTimeAsync(5000);
+        await el.updateComplete;
+
+        expect(scale(el)).toBeNull();
+        expect(vi.getTimerCount()).toBe(0);
+    });
+
     it('ignores a report about a track that is no longer loaded', async () => {
         pretendPhone(true);