Post the benchmark PR comment (both benchmarks) for fork PRs too

.github/workflows/bench-comment.yml

@@ -0,0 +1,103 @@
+# Posts the benchmark comparison comment produced by bench-compare.yml.
+#
+# bench-compare.yml runs on `pull_request`, where fork PRs get a read-only
+# token that cannot post comments. This workflow runs on `workflow_run` with
+# write permissions, downloads the comment artifact from the triggering run,
+# and creates/updates the marker-managed PR comment — for fork and same-repo
+# PRs alike.
+#
+# Security: this workflow has a write token but never checks out or executes
+# PR code. The artifact content is treated as data only; the PR number it
+# names is validated against the triggering run's head SHA before posting.
+name: Benchmark Comment
+
+on:
+  workflow_run:
+    workflows: ['Benchmark Comparison']
+    types: [completed]
+
+permissions:
+  actions: read
+  pull-requests: write
+
+jobs:
+  post-comment:
+    name: 'Post benchmark comment'
+    runs-on: ubuntu-latest
+    if: github.event.workflow_run.event == 'pull_request'
+
+    steps:
+      - uses: actions/download-artifact@v4
+        with:
+          name: bench-comment
+          run-id: ${{ github.event.workflow_run.id }}
+          github-token: ${{ secrets.GITHUB_TOKEN }}
+          path: comment-artifact
+
+      - name: Post PR comment
+        uses: actions/github-script@v7
+        with:
+          script: |
+            const fs = require('fs');
+            const marker = '<!-- bench-compare -->';
+
+            let body = fs.readFileSync('comment-artifact/bench-comment.md', 'utf8');
+            const prNumber = parseInt(
+              fs.readFileSync('comment-artifact/pr-number.txt', 'utf8').trim(),
+              10
+            );
+
+            if (!Number.isInteger(prNumber) || prNumber <= 0) {
+              core.setFailed(`Invalid PR number in artifact: ${prNumber}`);
+              return;
+            }
+
+            // The artifact was produced by an untrusted run; confirm the PR it
+            // names is the one the triggering run actually built.
+            const { data: pr } = await github.rest.pulls.get({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              pull_number: prNumber,
+            });
+            if (pr.head.sha !== context.payload.workflow_run.head_sha) {
+              core.info(
+                `PR #${prNumber} head (${pr.head.sha}) does not match the ` +
+                  `triggering run (${context.payload.workflow_run.head_sha}) — ` +
+                  'stale or mismatched artifact, skipping.'
+              );
+              return;
+            }
+
+            // GitHub comments cap at 65536 characters; keep the summary
+            // tables and truncate the tail (full output stays in the job
+            // summary of the triggering run).
+            const limit = 65000;
+            if (body.length > limit) {
+              body =
+                body.slice(0, limit) +
+                '\n```\n\n</details>\n\n> Output truncated — full results in the workflow job summary.\n';
+            }
+
+            const { data: comments } = await github.rest.issues.listComments({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              issue_number: prNumber,
+            });
+
+            const existing = comments.find((c) => c.body.includes(marker));
+
+            if (existing) {
+              await github.rest.issues.updateComment({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                comment_id: existing.id,
+                body,
+              });
+            } else {
+              await github.rest.issues.createComment({
+                owner: context.repo.owner,
+                repo: context.repo.repo,
+                issue_number: prNumber,
+                body,
+              });
+            }

.github/workflows/bench-compare.yml

@@ -57,46 +57,19 @@ jobs:
         if: always() && steps.checkout.outcome == 'success'
         run: cat "$RUNNER_TEMP/bench-comment.md" >> "$GITHUB_STEP_SUMMARY"
 
-      - name: Post PR comment
+      # This job runs with a read-only token for fork PRs, so it cannot post
+      # the comment itself. It uploads the comment body as an artifact and the
+      # privileged bench-comment.yml workflow (workflow_run) posts it — same
+      # path for fork and same-repo PRs.
+      - name: Upload comment artifact
         if: always() && steps.checkout.outcome == 'success'
-        uses: actions/github-script@v7
-        with:
-          script: |
-            const fs = require('fs');
-            const marker = '<!-- bench-compare -->';
-
-            const body = fs.readFileSync(process.env.RUNNER_TEMP + '/bench-comment.md', 'utf8');
-
-            const headFullName = context.payload.pull_request?.head?.repo?.full_name;
-            const isFork = !headFullName || headFullName !== context.repo.owner + '/' + context.repo.repo;
-
-            if (isFork) {
-              core.info('PR is from a fork — skipping PR comment (results are in the job summary).');
-              core.info('--- Comment body start ---');
-              core.info(body);
-              core.info('--- Comment body end ---');
-            } else {
-              const { data: comments } = await github.rest.issues.listComments({
-                owner: context.repo.owner,
-                repo: context.repo.repo,
-                issue_number: context.issue.number,
-              });
-
-              const existing = comments.find(c => c.body.includes(marker));
+        run: |
+          mkdir -p "$RUNNER_TEMP/comment-artifact"
+          cp "$RUNNER_TEMP/bench-comment.md" "$RUNNER_TEMP/comment-artifact/bench-comment.md"
+          echo "${{ github.event.pull_request.number }}" > "$RUNNER_TEMP/comment-artifact/pr-number.txt"
 
-              if (existing) {
-                await github.rest.issues.updateComment({
-                  owner: context.repo.owner,
-                  repo: context.repo.repo,
-                  comment_id: existing.id,
-                  body,
-                });
-              } else {
-                await github.rest.issues.createComment({
-                  owner: context.repo.owner,
-                  repo: context.repo.repo,
-                  issue_number: context.issue.number,
-                  body,
-                });
-              }
-            }
+      - uses: actions/upload-artifact@v4
+        if: always() && steps.checkout.outcome == 'success'
+        with:
+          name: bench-comment
+          path: ${{ runner.temp }}/comment-artifact/