chore: import upstream snapshot with attribution

showcase/integrations/langgraph-fastapi/qa/subagents.md

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+# QA: Sub-Agents — LangGraph (FastAPI)
+
+## Prerequisites
+
+- Demo is deployed and accessible
+- Agent backend is healthy (check `/api/copilotkit` GET — `agent_status: "reachable"`)
+- `OPENAI_API_KEY` is set in the agent environment
+
+## What this demo proves
+
+- A supervisor LLM exposes three sub-agents (`research_agent`,
+  `writing_agent`, `critique_agent`) as tools.
+- Each sub-agent is a real `create_agent(...)` with its own system
+  prompt — the supervisor does NOT just template-fill responses.
+- Every delegation appends an entry to the `delegations` slot of agent
+  state, which the UI renders live as a delegation log.
+
+## Test Steps
+
+### 1. Page loads with delegation log + chat
+
+- [ ] Navigate to `/demos/subagents`
+- [ ] The delegation log (`data-testid="delegation-log"`) is visible on the left
+- [ ] Header reads "Sub-agent delegations"
+- [ ] Counter (`data-testid="delegation-count"`) reads "0 calls"
+- [ ] Empty state copy: "Ask the supervisor to complete a task..."
+- [ ] Chat is visible on the right with placeholder "Give the supervisor a task..."
+
+### 2. Supervisor running indicator
+
+- [ ] Send the "Write a blog post" suggestion
+- [ ] Within ~2 seconds the `supervisor-running` badge appears on the log header
+- [ ] The badge has the pulsing dot and "Supervisor running" label
+
+### 3. Delegations appear live
+
+- [ ] As the run progresses, `delegation-entry` rows appear one at a time
+- [ ] Counter increments accordingly (1 calls, 2 calls, 3 calls)
+- [ ] Typical sequence on the "Write a blog post" suggestion:
+  - [ ] First entry shows the Research badge (`🔎 Research`)
+  - [ ] Second entry shows the Writing badge (`✍️ Writing`)
+  - [ ] Third entry shows the Critique badge (`🧐 Critique`)
+- [ ] Each entry shows the task on one line and the sub-agent's result
+      below it in the result panel
+- [ ] Each entry status shows `completed`
+
+### 4. Result quality (sanity check)
+
+- [ ] The research entry's result is a bulleted list of 3-5 facts
+- [ ] The writing entry's result is a single coherent paragraph
+- [ ] The critique entry's result is 2-3 bullet/critique items
+- [ ] When the supervisor finishes, the `supervisor-running` badge disappears
+
+### 5. Multiple runs accumulate
+
+- [ ] Send the "Explain a topic" suggestion next
+- [ ] Counter continues from previous total (does not reset)
+- [ ] New delegation entries are appended at the bottom
+
+### 6. Error handling
+
+- [ ] Sending an empty message is handled gracefully (no crash)
+- [ ] No console errors during a normal run
+
+## Expected Results
+
+- Chat loads within 3 seconds
+- First delegation appears within ~10 seconds of sending a task
+- A typical 3-step plan completes in under 60 seconds
+- No UI errors, broken layouts, or console warnings