Format only PR-changed files in web edit workflow

Instead of running prettier on all **/*.md files, fetch the list of
files changed in the PR via the GitHub API and format only those. This
broadens formatting to all file types prettier supports while keeping
the scope limited to what the PR actually touches.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: ntotten

.github/workflows/format.yaml

@@ -0,0 +1,92 @@
+name: Format (Web Edits)
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened]
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  format:
+    # Only attempt to push if the PR branch is in the same repo (not a fork)
+    if: ${{ github.event.pull_request.head.repo.full_name == github.repository }}
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Detect if PR contains Web UI commits
+        id: webui
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const { owner, repo } = context.repo;
+            const pr = context.payload.pull_request.number;
+
+            // List commits on the PR
+            const commits = await github.paginate(
+              github.rest.pulls.listCommits,
+              { owner, repo, pull_number: pr, per_page: 100 }
+            );
+
+            // GitHub web editor commits are typically committed by `web-flow`
+            const hasWebFlow = commits.some(c => c.committer?.login === "web-flow");
+
+            core.setOutput("is_webui", hasWebFlow ? "true" : "false");
+
+      - name: Checkout PR branch
+        if: ${{ steps.webui.outputs.is_webui == 'true' }}
+        uses: actions/checkout@v4
+        with:
+          ref: ${{ github.event.pull_request.head.ref }}
+          fetch-depth: 0
+
+      - name: Setup Node
+        if: ${{ steps.webui.outputs.is_webui == 'true' }}
+        uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: npm
+
+      - name: Install deps
+        if: ${{ steps.webui.outputs.is_webui == 'true' }}
+        run: npm ci
+
+      - name: Get changed files
+        if: ${{ steps.webui.outputs.is_webui == 'true' }}
+        id: changed
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const { owner, repo } = context.repo;
+            const pr = context.payload.pull_request.number;
+
+            const files = await github.paginate(
+              github.rest.pulls.listFiles,
+              { owner, repo, pull_number: pr, per_page: 100 }
+            );
+
+            // Only include added or modified files (not removed)
+            const paths = files
+              .filter(f => f.status !== "removed")
+              .map(f => f.filename);
+
+            core.setOutput("files", paths.join("\n"));
+
+      - name: Format changed files
+        if: ${{ steps.webui.outputs.is_webui == 'true' && steps.changed.outputs.files != '' }}
+        run: |
+          echo "${{ steps.changed.outputs.files }}" | xargs npx prettier --write --ignore-unknown
+
+      - name: Commit & push (only if changes)
+        if: ${{ steps.webui.outputs.is_webui == 'true' }}
+        run: |
+          if git diff --quiet; then
+            echo "No changes."
+            exit 0
+          fi
+          git config user.name "github-actions[bot]"
+          git config user.email "github-actions[bot]@users.noreply.github.com"
+          git add -A
+          git commit -m "chore: format files (web UI PR)"
+          git push