test(player): pin the phone transport, and the desktop bar not moving

Ten tests, five of which fail on the build before this. The desktop
guard is meant to pass there -- that is its job, and it is the one that
caught a three-pixel regression nothing else could see.

`openTheQueue` moves to the fixtures, because hiding one button failed
ten tests in four files about the back stack and about layout: every
one of them opened the queue by clicking `#queue-button`, and so was
quietly asserting *which* route exists as well as what the queue does.
The route differs by width now and that is the feature.

Two smaller things. The play button is named for its action, so an
exact 'Play' waits out a fixture track -- 11.1s per test, passing by
luck, and it would have failed outright against LONG_TRACK. And the
"nothing playing" case clears the queue itself rather than trusting the
app not to have played anything: `make e2e` runs one long-lived app
across every spec (#168), which is how a deterministic bug first showed
up as a flake.

e2e/support/fixtures.ts

@@ -140,6 +140,50 @@ export async function navigateTo(page: Page, view: string): Promise<void> {
     .waitFor({ state: 'attached' });
 }
 
+/**
+ * Open the queue the way a user at this viewport would.
+ *
+ * **The route differs by width and that is the feature, not an
+ * inconvenience.** Above 600px the bottom bar carries a queue button.
+ * Below it that button is gone (#59) and the queue is reached from the
+ * full-screen Now Playing view, which the mini player's art opens —
+ * "reachable only from Now Playing", which is what the issue asks for.
+ *
+ * It is here rather than in one spec because four files need it, and
+ * because a spec that hard-codes `#queue-button` is quietly asserting
+ * *which* route exists as well as what the queue does. Four of them
+ * were, which is how hiding one button failed ten tests about
+ * something else.
+ *
+ * The width is read from the page rather than passed, so a caller that
+ * resizes and then opens does not have to say so twice.
+ */
+export async function openTheQueue(page: Page): Promise<void> {
+  const toggle = page.locator('#queue-button');
+
+  if (await toggle.isVisible()) {
+    if ((await toggle.getAttribute('aria-expanded')) !== 'true') {
+      await toggle.click();
+    }
+
+    await expect(toggle).toHaveAttribute('aria-expanded', 'true');
+
+    return;
+  }
+
+  // The phone: through Now Playing. `open-now-playing` is the mini
+  // player's art, which is a button only below 600px.
+  if (
+    (await page.getByTestId('main-content').getAttribute('data-active-view')) !==
+    'now-playing'
+  ) {
+    await page.getByTestId('open-now-playing').click();
+  }
+
+  await page.getByTestId('npv-queue').click();
+  await expect(page.locator('#queue-panel')).toHaveAttribute('open', '');
+}
+
 /** Thin client for the dev-only /__test/ surface (backend/testctl). */
 export class TestCtl {
   constructor(private readonly baseURL: string) {}