Fix automerge: add workflow_run trigger after CI completes

check_suite and status events don't reliably trigger for workflows
on the same commit (GitHub prevents infinite loops). Replaced with
workflow_run on CI completion, which fires after all CI jobs finish.

Added comments explaining why each trigger group exists.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/automerge.yml

@@ -1,5 +1,12 @@
 name: Automerge
 
+# Triggers:
+# - pull_request: fires when PR is opened, labeled, updated, etc.
+#   Handles the case where the label is added after CI already passed.
+# - workflow_run (CI): fires after the CI workflow completes.
+#   This is needed because check_suite and status events don't reliably
+#   fire for workflows on the same commit (GitHub prevents infinite loops).
+#   Without this, the automerge action never retries after CI passes.
 on:
   pull_request:
     types:
@@ -14,10 +21,10 @@ on:
   pull_request_review:
     types:
       - submitted
-  check_suite:
+  workflow_run:
+    workflows: ["CI"]
     types:
       - completed
-  status: {}
 
 env:
   FORCE_JAVASCRIPT_ACTIONS_TO_NODE24: true