chore: import upstream snapshot with attribution

showcase/integrations/claude-sdk-python/qa/multimodal.md

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+# QA: Multimodal Attachments — Claude Agent SDK (Python)
+
+## Prerequisites
+
+- Demo is deployed and accessible
+- Agent backend is healthy (check /api/health)
+- `ANTHROPIC_API_KEY` is set on the deployment
+- `pypdf` is installed in the backend environment (listed in
+  `requirements.txt`)
+
+## Test Steps
+
+### 1. Basic Functionality
+
+- [ ] Navigate to `/demos/multimodal`
+- [ ] Verify the "Multimodal attachments" header renders
+- [ ] Verify the bundled-samples row shows "Try with sample image" and
+      "Try with sample PDF" buttons
+- [ ] Verify the paperclip button is visible on the chat composer
+
+### 2. Feature-Specific Checks
+
+#### Sample image
+
+- [ ] Click "Try with sample image" — the button should flip to
+      "Loading…" briefly
+- [ ] Verify the CopilotChat attachment strip shows a pending
+      `sample.png` chip
+- [ ] Type "What's in this image?" and send
+- [ ] Verify Claude's reply references concrete visual details (e.g.
+      colors, objects) from the bundled PNG
+
+#### Sample PDF
+
+- [ ] Click "Try with sample PDF"
+- [ ] Verify the `sample.pdf` chip appears
+- [ ] Type "Summarise this document" and send
+- [ ] Verify Claude replies with a short summary of the PDF's actual
+      content (not a generic "I cannot read PDFs" reply)
+
+### 3. LFS-pointer guard
+
+- [ ] If the deployment accidentally ships a Git LFS pointer instead of
+      the real binary, clicking a sample button should surface
+      `data-testid="multimodal-sample-error"` with an actionable message
+
+### 4. Error Handling
+
+- [ ] No console errors during normal usage.
+- [ ] Upload a file over 10 MB and verify the attachment is rejected
+      with a visible toast.
+
+## Expected Results
+
+- Image replies reference real visual details (not generic).
+- PDF replies reference document-specific content.
+- No silent dropping of attachments.