Fix bench-compare workflow for fork PRs

Use github.event.pull_request.head.sha instead of github.head_ref
for the checkout ref, since head_ref is a branch name that only
exists on the fork remote and causes checkout to fail for fork PRs.

Also guard post-bench steps with steps.checkout.outcome == 'success'
so they don't fail when checkout itself fails.

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

Author: Copilot

.github/workflows/bench-compare.yml

@@ -18,10 +18,13 @@ jobs:
 
     steps:
       - uses: actions/checkout@v6
+        id: checkout
         with:
           # Full history so the script can git-archive the base branch.
           fetch-depth: 0
-          ref: ${{ github.head_ref }}
+          # Use the PR head SHA so fork PRs resolve correctly
+          # (github.head_ref is a branch name that only exists on the fork remote).
+          ref: ${{ github.event.pull_request.head.sha }}
 
       - uses: wyvox/action-setup-pnpm@v3
 
@@ -33,19 +36,19 @@ jobs:
           pnpm bench:compare | sed 's/\x1b\[[0-9;]*m//g' > "$RUNNER_TEMP/bench-output.txt"
 
       - name: Format PR comment
-        if: always()
+        if: always() && steps.checkout.outcome == 'success'
         env:
           BENCH_OUTPUT_FILE: ${{ runner.temp }}/bench-output.txt
           BENCH_JSON_OUTPUT: ${{ runner.temp }}/bench-results.json
           BENCH_JOB_SUCCESS: ${{ job.status == 'success' }}
         run: node scripts/format-bench-comment.mjs > "$RUNNER_TEMP/bench-comment.md"
 
       - name: Write job summary
-        if: always()
+        if: always() && steps.checkout.outcome == 'success'
         run: cat "$RUNNER_TEMP/bench-comment.md" >> "$GITHUB_STEP_SUMMARY"
 
       - name: Post PR comment
-        if: always()
+        if: always() && steps.checkout.outcome == 'success'
         uses: actions/github-script@v7
         with:
           script: |