first pass at trying to get failed rustfmt summary as comment

.github/workflows/ci.yml

@@ -30,6 +30,9 @@ jobs:
   format:
     name: cargo fmt
     runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      pull-requests: write
     steps:
       - uses: actions/checkout@v4
       - name: Setup Rustfmt
@@ -39,3 +42,20 @@ jobs:
           components: rustfmt
       - name: Rustfmt Check
         uses: actions-rust-lang/rustfmt@v1
+      - name: Save Failure Summary (if needed)
+        if: failure()
+        run: echo "$GITHUB_STEP_SUMMARY" > summary.md
+      - name: Comment Failure Summary (if needed)
+        if: failure() && github.event_name == 'pull_request'
+        uses: actions/github-script@v7
+        with:
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          script: |
+            const fs = require('fs');
+            const summary = fs.readFileSync('summary.md', 'utf8');
+            github.rest.issues.createComment({
+              issue_number: context.issue.number,
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              body: summary
+            });