fix: surface Spotify quota exhaustion

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

frontend/tests/resultPresentation.test.ts

@@ -166,6 +166,34 @@ describe('result presentation', () => {
     expect(onPick).toHaveBeenCalledWith('Focus')
   })
 
+  it('renders a quota error without retry and keeps the demo escape hatch', () => {
+    const turn: AssistantTurn = {
+      ...doneTurn(),
+      status: 'error',
+      tracks: [],
+      warnings: [],
+      error: {
+        type: 'error',
+        code: 'quota_exhausted',
+        message: "Spotify's Development Mode quota is temporarily exhausted.",
+      },
+      completion: null,
+    }
+    const demoUrl = 'https://demo.example.com'
+    const root = mountComponent(AssistantMessage, {
+      turn,
+      canSave: false,
+      demoUrl,
+    })
+    const alert = root.querySelector<HTMLElement>('[role="alert"]')
+    const demoLink = alert?.querySelector<HTMLAnchorElement>('a')
+
+    expect(alert?.dataset.errorCode).toBe('quota_exhausted')
+    expect(alert?.querySelector('button')).toBeNull()
+    expect(demoLink?.href).toBe(`${demoUrl}/`)
+    expect(demoLink?.textContent).toContain('Open the demo instance')
+  })
+
   it('renders a first-stage stream error with its code and message', () => {
     const turn: AssistantTurn = {
       ...doneTurn(),