fix(frontend): refine streamed presentation and resolve stream edge cases

frontend/tests/recommendationStream.test.ts

@@ -128,8 +128,23 @@ describe('streamRecommendations', () => {
     expect(wasCancelled).toBe(true)
   })
 
+  it('accepts a terminal error as the only event', async () => {
+    const error = { type: 'error', code: 'first_stage_failed', message: 'Planning failed.' }
+    stubResponse(streamResponse([encoder.encode(`${JSON.stringify(error)}\n`)]))
+    const events: StreamEvent[] = []
+
+    await streamRecommendations(
+      { schema_version: 1, query: 'focus', history: [], prior_recommendations: [] },
+      new AbortController().signal,
+      (event) => events.push(event),
+    )
+
+    expect(events).toEqual([error])
+  })
+
   it.each([
     ['an event before metadata', [{ type: 'warning', code: 'early', message: 'No metadata.' }]],
+    ['done before metadata', [{ type: 'done', track_count: 0, total_ms: 4 }]],
     [
       'duplicate metadata',
       [