diff --git a/.github/workflows/pr-auto-review.yml b/.github/workflows/pr-auto-review.yml
index 7dc5a780..ab549d96 100644
--- a/.github/workflows/pr-auto-review.yml
+++ b/.github/workflows/pr-auto-review.yml
@@ -44,24 +44,28 @@ on:
 
 permissions: {}
 
-# Deduplicate ONLY pull_request events which have a direct PR context (issue #1126).
-# On GitHub Free (20 concurrent jobs, org-wide), avoid race conditions when multiple
-# PRs share a commit:
-#   • pull_request / pull_request_review — have github.event.pull_request.number;
-#     safe to collapse per PR and cancel in progress.
-#   • check_suite / workflow_run — only have pull_requests[] array; if multiple PRs
-#     share the commit, pull_requests[0] is indeterminate and causes the first PR's
-#     events to cancel the second PR's events. Use unique per-run groups instead.
-# A trigger with no associated PR (fork / no PR) also falls back to unique-per-run
-# so unrelated workflow runs never interfere.
+# Deduplicate ONLY the default-branch-context triggers (issue #1126). On GitHub
+# Free (20 concurrent jobs, org-wide) this stub fanned out per trigger. Its runs
+# split by context:
+#   • check_suite / workflow_run — head_branch=main, the check does NOT attach to
+#     the PR head, so superseding an in-flight run is SAFE. Both events collapse
+#     onto one group per PR (`…-pr-<number>`) with cancel-in-progress: true.
+#   • pull_request / pull_request_review — run on the PR head; a cancelled run
+#     would leave a cancelled `pr-auto-review / check-and-dispatch` check on the
+#     head. They get a unique-per-run group and never cancel — note this differs
+#     from the previous per-PR group + cancel-in-progress: true behaviour.
+# A default-branch trigger with no associated PR (fork / no PR) also falls back to
+# the unique-per-run group so unrelated PRs never collapse into one group.
 concurrency:
   group: >-
     ${{
-    (github.event_name == 'pull_request' && format('pr-auto-review-ready-check-pr-{0}', github.event.pull_request.number))
-    || (github.event_name == 'pull_request_review' && format('pr-auto-review-ready-check-pr-{0}', github.event.pull_request.number))
+    (github.event_name == 'check_suite' && github.event.check_suite.pull_requests[0].number)
+    && format('pr-auto-review-ready-check-pr-{0}', github.event.check_suite.pull_requests[0].number)
+    || (github.event_name == 'workflow_run' && github.event.workflow_run.pull_requests[0].number)
+    && format('pr-auto-review-ready-check-pr-{0}', github.event.workflow_run.pull_requests[0].number)
     || format('pr-auto-review-ready-check-unique-{0}', github.run_id)
     }}
-  cancel-in-progress: ${{ github.event_name == 'pull_request' || github.event_name == 'pull_request_review' }}
+  cancel-in-progress: ${{ github.event_name == 'check_suite' || github.event_name == 'workflow_run' }}
 
 jobs:
   pr-auto-review: