From cef203ded670d824d06f66895b5dacd7dd4bd22d Mon Sep 17 00:00:00 2001
From: Claude <noreply@anthropic.com>
Date: Tue, 9 Jun 2026 22:01:20 +0000
Subject: [PATCH 1/2] Serialize workflow runs per PR
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Two runs can act on the same PR concurrently: the push that finishes a
conflict resolution fires a synchronize event while the conflict label
is still attached, so the follow-up run races the one that triggered it
(the label is its gate and only comes off at the end). A per-PR
concurrency group queues the follow-up instead; cancel-in-progress stays
off so a running update is never killed mid-mutation. The group is
keyed by PR number rather than repo-wide because GitHub keeps only the
newest pending run in a group - a repo-wide group could silently drop
the update for one merge when several land in quick succession.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

https://claude.ai/code/session_01JHvKryT4QUpHYdNq9YEQxX
---
 .github/workflows/update-pr-stack.yml | 7 +++++++
 README.md                             | 8 ++++++++
 2 files changed, 15 insertions(+)

diff --git a/.github/workflows/update-pr-stack.yml b/.github/workflows/update-pr-stack.yml
index 87cf4ea..86f030c 100644
--- a/.github/workflows/update-pr-stack.yml
+++ b/.github/workflows/update-pr-stack.yml
@@ -9,6 +9,13 @@ permissions:
   contents: write
   pull-requests: write
 
+# Serialize runs per PR: the push that finishes a conflict resolution fires a
+# synchronize event while the conflict label is still attached, so without a
+# group the follow-up run races the one that triggered it.
+concurrency:
+  group: update-pr-stack-${{ github.event.pull_request.number }}
+  cancel-in-progress: false
+
 jobs:
   update-pr-stack:
     runs-on: ubuntu-latest
diff --git a/README.md b/README.md
index 6e19752..f0737ae 100644
--- a/README.md
+++ b/README.md
@@ -79,6 +79,10 @@ on:
   pull_request:
     types: [closed, synchronize]
 
+concurrency:
+  group: update-pr-stack-${{ github.event.pull_request.number }}
+  cancel-in-progress: false
+
 jobs:
   update-pr-stack:
     runs-on: ubuntu-latest
@@ -110,6 +114,10 @@ permissions:
   contents: write
   pull-requests: write
 
+concurrency:
+  group: update-pr-stack-${{ github.event.pull_request.number }}
+  cancel-in-progress: false
+
 jobs:
   update-pr-stack:
     runs-on: ubuntu-latest

From 0f7a4b26a03334c1aac7db1d5ba06342b834523c Mon Sep 17 00:00:00 2001
From: Claude <noreply@anthropic.com>
Date: Tue, 9 Jun 2026 22:14:12 +0000
Subject: [PATCH 2/2] Tolerate pending workflow runs in the e2e monitor
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

A run waiting on its concurrency-group slot reports status "pending",
which the wait loop treated as fatal instead of sleeping. Surfaced as
soon as the per-PR concurrency group queued a merge-triggered run
behind a still-running synchronize run.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

https://claude.ai/code/session_01JHvKryT4QUpHYdNq9YEQxX
---
 tests/test_e2e.sh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tests/test_e2e.sh b/tests/test_e2e.sh
index 420f2cd..b6e9f19 100755
--- a/tests/test_e2e.sh
+++ b/tests/test_e2e.sh
@@ -558,7 +558,7 @@ wait_for_synchronize_workflow() {
                 log_cmd gh run view "$target_run_id" --repo "$REPO_FULL_NAME" --log || echo >&2 "Could not fetch logs for run $target_run_id"
                 return 1
             fi
-        elif [[ "$run_status" == "queued" || "$run_status" == "in_progress" || "$run_status" == "waiting" ]]; then
+        elif [[ "$run_status" == "queued" || "$run_status" == "in_progress" || "$run_status" == "waiting" || "$run_status" == "pending" ]]; then
             echo >&2 "Workflow $target_run_id is $run_status. Sleeping $sleep_time seconds."
         else
             echo >&2 "Workflow $target_run_id has unexpected status: $run_status. Conclusion: $run_conclusion"
@@ -665,7 +665,7 @@ wait_for_workflow() {
                 log_cmd gh run view "$target_run_id" --repo "$REPO_FULL_NAME" --log || echo >&2 "Could not fetch logs for run $target_run_id"
                 return 1
             fi
-        elif [[ "$run_status" == "queued" || "$run_status" == "in_progress" || "$run_status" == "waiting" ]]; then
+        elif [[ "$run_status" == "queued" || "$run_status" == "in_progress" || "$run_status" == "waiting" || "$run_status" == "pending" ]]; then
             echo >&2 "Workflow $target_run_id is $run_status. Sleeping $sleep_time seconds."
         else
             echo >&2 "Workflow $target_run_id has unexpected status: $run_status. Conclusion: $run_conclusion"