fix: use git worktree for gh-pages operations (#23)

## Summary

- Replace branch switching with `git worktree` in `deploy-to-gh-pages`
and `update-index` actions
- The main checkout is never disturbed, fixing the error where
`update-index` action could not be found after deploying
- Update "Update latest" step in `docs-release.yml` to use worktree as
well

## Test plan

- [ ] Push to main → `/dev/` deployed, `index.html` updated (no action
lookup error)
- [ ] Push a tag → `/<version>/`, `/latest/`, and `index.html` all
updated

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

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: TaiSakuma

.github/actions/deploy-to-gh-pages/action.yml

@@ -15,28 +15,39 @@ inputs:
 outputs:
   url:
     description: Default GitHub Pages URL for the deployed subdirectory
-    value: ${{ steps.deploy.outputs.url }}
+    value: ${{ steps.url.outputs.url }}
 
 runs:
   using: composite
   steps:
-    - id: deploy
-      shell: bash
+    # Create a worktree for gh-pages.
+    - shell: bash
       run: |
-        TARGET="${{ inputs.target }}"
         git fetch origin gh-pages 2>/dev/null || true
         if git rev-parse --verify origin/gh-pages >/dev/null 2>&1; then
-          git checkout -B gh-pages origin/gh-pages
+          git worktree add /tmp/gh-pages gh-pages
         else
-          git checkout --orphan gh-pages
-          git rm -rf .
-          git clean -fd
+          git worktree add --orphan -b gh-pages /tmp/gh-pages
         fi
+
+    # Copy the built site into the target subdirectory, commit, and push.
+    - shell: bash
+      run: |
+        cd /tmp/gh-pages
+        TARGET="${{ inputs.target }}"
         rm -rf "$TARGET"
         mkdir -p "$(dirname "$TARGET")"
         cp -r "${{ inputs.site-dir }}" "$TARGET"
         touch .nojekyll
         git add .nojekyll "$TARGET"
         git diff --cached --quiet || git commit -m "${{ inputs.commit-message }}"
         git push origin gh-pages
-        echo "url=https://${{ github.repository_owner }}.github.io/${{ github.event.repository.name }}/${TARGET}/" >> "$GITHUB_OUTPUT"
+
+    # Clean up the worktree.
+    - shell: bash
+      run: git worktree remove /tmp/gh-pages
+
+    # Output the default GitHub Pages URL for the deployed subdirectory.
+    - id: url
+      shell: bash
+      run: echo "url=https://${{ github.repository_owner }}.github.io/${{ github.event.repository.name }}/${{ inputs.target }}/" >> "$GITHUB_OUTPUT"

.github/actions/update-index/action.yml

@@ -12,11 +12,21 @@ inputs:
 runs:
   using: composite
   steps:
+    # Create a worktree for gh-pages.
+    - shell: bash
+      run: git worktree add /tmp/gh-pages gh-pages
+
+    # Generate index.html, commit, and push.
     - shell: bash
       run: |
+        cd /tmp/gh-pages
         python "${{ github.action_path }}/generate_index.py" \
           "${{ inputs.repo-name }}" \
           "${{ inputs.repo-url }}"
         git add index.html
         git diff --cached --quiet || git commit -m "Update index.html"
         git push origin gh-pages
+
+    # Clean up the worktree.
+    - shell: bash
+      run: git worktree remove /tmp/gh-pages

.github/workflows/docs-release.yml

@@ -49,10 +49,15 @@ jobs:
 
       - name: Update latest
         run: |
+          git worktree add /tmp/gh-pages gh-pages
+          cd /tmp/gh-pages
           rm -rf latest
           cp -r "${{ steps.build.outputs.site-dir }}" latest
           git add latest
           git commit -m "Update latest"
+          git push origin gh-pages
+
+      - run: git worktree remove /tmp/gh-pages
 
       - uses: ./.github/actions/update-index
         with: