test: read SSE chunks until session.updated arrives

session.status and session.updated are two separate res.write calls, so the
test failed whenever TCP delivered them in different chunks.

extensions/piagentui-server.test.ts

@@ -1025,8 +1025,13 @@ describe('PiAgentUi Extension Server', () => {
 
     // Trigger agent_start - should broadcast session.status and session.updated!
     await listeners['agent_start']()
-    const chunk3 = await reader?.read()
-    const text3 = new TextDecoder().decode(chunk3?.value)
+    // The two events are separate writes, so TCP may deliver them in different chunks.
+    let text3 = ''
+    while (!text3.includes('session.updated')) {
+      const chunk = await reader?.read()
+      if (!chunk || chunk.done) break
+      text3 += new TextDecoder().decode(chunk.value)
+    }
     expect(text3).toContain('session.status')
     expect(text3).toContain('working')
     expect(text3).toContain('session.updated')