chore: import upstream snapshot with attribution

showcase/integrations/claude-sdk-python/qa/headless-complete.md

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+# QA: Headless Chat (Complete) — Claude Agent SDK (Python)
+
+## Prerequisites
+
+- Demo is deployed and accessible
+- Agent backend is healthy
+- ANTHROPIC_API_KEY is set
+
+## Test Steps
+
+### 1. Basic Functionality
+
+- [ ] Navigate to `/demos/headless-complete`
+- [ ] Verify the custom chat surface renders (header, scrollable list, input bar)
+- [ ] Verify NO `<CopilotChat />` imports are visible (all chrome is custom)
+- [ ] Send "Hello" — verify the user bubble + assistant bubble render
+
+### 2. Generative UI Weave
+
+- [ ] Click the "Weather in Tokyo" suggestion — verify the WeatherCard renders inline
+- [ ] Click the "Highlight a note" suggestion — verify the HighlightNote component renders
+- [ ] Try a message that triggers other tools — verify the catch-all tool card renders
+
+### 3. Lifecycle
+
+- [ ] During agent response, verify the Send button swaps to Stop
+- [ ] Click Stop — verify the agent cancels cleanly
+- [ ] Verify no console errors after stop
+
+## Expected Results
+
+- Messages area with `data-testid="headless-complete-messages"` scrolls automatically
+- Input disabled while running; Send button disabled when empty