test(554): pin both clears the hint's single guard depends on

Dropping the onPlaying clear made the `state === 'starting'` render guard the
hint's only guard, which moves the burden onto the two paths back to
`starting`: each has to clear `autoplayBlocked` itself. Both were assertable
but unasserted — either `setAutoplayBlocked(false)` could be deleted with the
whole panel suite green, so the invariant the code comment and
docs/spa-conventions.md §5b both state was unpinned in both of its named paths.

Add one test per path (Retry; a channel switch), each asserting the hint is
gone while the panel is back at `starting` — so the render guard cannot be
what hid it. Each also asserts the player really re-mounted (loadSource count
/ last URL, plus a non-null <video>), so the hint cannot be absent merely
because the `resolvedSrc` block is unrendered.

Measured on this tree, each mutation caught by exactly one test:
deleting the onRetry clear reds only 'clicking Retry clears the
autoplay-blocked hint' (Tests 1 failed | 25 passed); deleting the
render-phase reset clear reds only 'clears the autoplay-blocked hint when
switching to a different channel' (1 failed | 25 passed); replacing
`autoplayBlocked && state === 'starting' &&` with `autoplayBlocked &&` reds
one test too. Unmutated: 26 passed.

Refs #554

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015QqCpYFsKgnAnx6jVwrKiV

web/src/screens/channels/ChannelPreviewPanel.test.tsx

@@ -273,6 +273,45 @@ describe('ChannelPreviewPanel', () => {
     }
   });
 
+  // The `state === 'starting'` guard is the hint's ONLY guard, so every path back to `starting` has
+  // to clear the flag itself. Retry is one: it is a fresh attempt that was never blocked, and a hint
+  // carried over from the previous attempt would name a cause that did not happen this time.
+  it('clicking Retry clears the autoplay-blocked hint', async () => {
+    const playSpy = vi
+      .spyOn(HTMLMediaElement.prototype, 'play')
+      .mockRejectedValue(new DOMException('blocked', 'NotAllowedError'));
+
+    try {
+      await renderPanel(
+        <ChannelPreviewPanel channel={channel(available)} nowPlaying={null} onClose={vi.fn()} open />
+      );
+
+      const manifestHandler = getManifestHandler();
+      await act(async () => {
+        manifestHandler();
+        await Promise.resolve();
+        await Promise.resolve();
+      });
+
+      expect(screen.getByText(/autoplay was blocked/i)).toBeInTheDocument();
+
+      // The retried attempt is not blocked.
+      playSpy.mockResolvedValue(undefined);
+      fireEvent.click(screen.getByRole('button', { name: /retry/i }));
+      await flush();
+
+      // The player really did re-mount, so the hint is absent because the flag was cleared — not
+      // because the whole `resolvedSrc` block is still unrendered.
+      expect(hlsMock.loadSource).toHaveBeenCalledTimes(2);
+      expect(document.querySelector('video')).not.toBeNull();
+      expect(screen.queryByText(/autoplay was blocked/i)).not.toBeInTheDocument();
+      // Retry returns to `starting`, so the render guard is not what hid the hint here.
+      expect(screen.getByText('starting')).toBeInTheDocument();
+    } finally {
+      playSpy.mockRestore();
+    }
+  });
+
   // A play() interrupted by teardown rejects with AbortError, which is exactly what Retry produces
   // while the manifest-parsed play() is still pending. The hint names blocked autoplay as the cause,
   // so it must not appear for a rejection that was not the autoplay policy.
@@ -495,6 +534,47 @@ describe('ChannelPreviewPanel', () => {
       expect(screen.getByText('playing')).toBeInTheDocument();
     });
 
+    // The other path back to `starting`, and the other half of the hint's single-guard invariant: a
+    // switch must not leave the previous channel's hint standing over a new channel that was never
+    // blocked. The render-phase reset owns this clear — the guard cannot help, since the new channel
+    // starts in `starting` too.
+    it('clears the autoplay-blocked hint when switching to a different channel', async () => {
+      const playSpy = vi
+        .spyOn(HTMLMediaElement.prototype, 'play')
+        .mockRejectedValue(new DOMException('blocked', 'NotAllowedError'));
+
+      try {
+        const { rerender } = await renderPanel(
+          <ChannelPreviewPanel channel={channel(available, undefined, 1)} nowPlaying={null} onClose={vi.fn()} open />
+        );
+
+        const manifestHandler = getManifestHandler();
+        await act(async () => {
+          manifestHandler();
+          await Promise.resolve();
+          await Promise.resolve();
+        });
+
+        expect(screen.getByText(/autoplay was blocked/i)).toBeInTheDocument();
+
+        // The new channel's attempt is not blocked.
+        playSpy.mockResolvedValue(undefined);
+        rerender(
+          <ChannelPreviewPanel channel={channel(available2, undefined, 2)} nowPlaying={null} onClose={vi.fn()} open />
+        );
+        await flush();
+
+        // The new channel's player really is mounted, so the hint is absent because the flag was
+        // cleared — not because the `resolvedSrc` block is still unrendered.
+        expect(hlsMock.loadSource).toHaveBeenLastCalledWith('/iptv/channel/34.1.m3u8');
+        expect(document.querySelector('video')).not.toBeNull();
+        expect(screen.queryByText(/autoplay was blocked/i)).not.toBeInTheDocument();
+        expect(screen.getByText('starting')).toBeInTheDocument();
+      } finally {
+        playSpy.mockRestore();
+      }
+    });
+
     it('does not carry the retry play token over to the next channel', async () => {
       // Both channels share a manifest URL so the only thing that could re-trigger the attach
       // effect across the switch is playToken. If the reset failed to zero it out, the token