Add notebook diff workflow for PR comments (anthropics#277)

* feat: add GitHub Action to post notebook diffs in PR comments

- Automatically detects changed .ipynb files in PRs
- Generates nbdime diffs for each changed notebook
- Posts formatted comment with collapsible diff sections
- Handles multiple notebooks and new files gracefully

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

* fix: use --system flag for uv pip install in workflow

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

* fix: use uvx to run nbdiff without installation

Using uvx --from nbdime nbdiff creates an ephemeral environment
and avoids issues with system Python being externally managed.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

* feat: add nbdiff flags to ignore non-content changes

Adds flags to focus diff on actual content:
- --ignore-attachments: Skip attachment changes
- --ignore-metadata: Skip metadata changes
- --ignore-identifiers: Skip cell ID changes
- --ignore-details: Skip execution counts, etc.

This makes the diff more readable and focused on code/markdown changes.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

* fix: use correct nbdiff ignore flag syntax

Use short flags (-A -M -I -D) instead of long form flags that don't exist.

- -A: ignore attachments
- -M: ignore metadata
- -I: ignore identifiers (cell IDs)
- -D: ignore details (execution counts, etc.)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

---------

Co-authored-by: Claude <[email protected]>

Author: PedramNavid

.github/workflows/notebook-diff-comment.yml

@@ -0,0 +1,97 @@
+name: Notebook Diff Comment
+
+on:
+  pull_request:
+    paths:
+      - '**/*.ipynb'
+
+permissions:
+  contents: read
+  pull-requests: write
+
+jobs:
+  post-notebook-diff:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0  # Need full history to diff against base
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@v4
+        with:
+          enable-cache: true
+
+      - name: Set up Python 3.11
+        run: uv python install 3.11
+
+      - name: Get changed notebooks
+        id: changed-notebooks
+        run: |
+          # Get the base branch (usually main)
+          BASE_SHA=${{ github.event.pull_request.base.sha }}
+          HEAD_SHA=${{ github.event.pull_request.head.sha }}
+
+          # Find all changed .ipynb files
+          CHANGED_NOTEBOOKS=$(git diff --name-only $BASE_SHA $HEAD_SHA | grep '\.ipynb$' || true)
+
+          if [ -z "$CHANGED_NOTEBOOKS" ]; then
+            echo "No notebooks changed"
+            echo "has_changes=false" >> $GITHUB_OUTPUT
+          else
+            echo "Changed notebooks:"
+            echo "$CHANGED_NOTEBOOKS"
+            echo "has_changes=true" >> $GITHUB_OUTPUT
+            # Save to file for next step
+            echo "$CHANGED_NOTEBOOKS" > changed_notebooks.txt
+          fi
+
+      - name: Generate notebook diffs
+        if: steps.changed-notebooks.outputs.has_changes == 'true'
+        run: |
+          BASE_SHA=${{ github.event.pull_request.base.sha }}
+          HEAD_SHA=${{ github.event.pull_request.head.sha }}
+
+          # Create output file
+          echo "# Notebook Changes" > diff_comment.md
+          echo "" >> diff_comment.md
+          echo "This PR modifies the following notebooks:" >> diff_comment.md
+          echo "" >> diff_comment.md
+
+          # Process each changed notebook
+          while IFS= read -r notebook; do
+            if [ -z "$notebook" ]; then
+              continue
+            fi
+
+            echo "Processing: $notebook"
+            echo "## 📓 \`$notebook\`" >> diff_comment.md
+            echo "" >> diff_comment.md
+            echo "<details>" >> diff_comment.md
+            echo "<summary>View diff</summary>" >> diff_comment.md
+            echo "" >> diff_comment.md
+            echo '```diff' >> diff_comment.md
+
+            # Generate diff (suppress errors if file doesn't exist in base)
+            # Ignore metadata, attachments, IDs, and other non-content changes
+            uvx --from nbdime nbdiff --no-color -A -M -I -D \
+              $BASE_SHA $HEAD_SHA "$notebook" 2>/dev/null >> diff_comment.md || echo "New file" >> diff_comment.md
+
+            echo '```' >> diff_comment.md
+            echo "" >> diff_comment.md
+            echo "</details>" >> diff_comment.md
+            echo "" >> diff_comment.md
+          done < changed_notebooks.txt
+
+          echo "---" >> diff_comment.md
+          echo "" >> diff_comment.md
+          echo "*Generated by nbdime*" >> diff_comment.md
+
+      - name: Post comment to PR
+        if: steps.changed-notebooks.outputs.has_changes == 'true'
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          # Post the comment
+          gh pr comment ${{ github.event.pull_request.number }} --body-file diff_comment.md