Atomic stack merge incorrectly reports missing CODEOWNER approval

[yoperiquoi]

Summary

gh stack merge rejects an otherwise mergeable stack with a missing CODEOWNER review error, although every pull request is approved on its current head commit by a reviewer who GitHub recognizes as a member of a required CODEOWNERS team.

Stack

• Three open pull requests in one linear stack
• Bottom PR targets the protected default branch
• Middle and top PRs target the preceding stack branches
• All three PRs report mergeStateStatus: CLEAN
• All three PRs report reviewDecision: APPROVED

Branch protection

The stack base branch requires:

• One approving review
• CODEOWNER review
• Stale review dismissal

The repository CODEOWNERS rules have a default owner group and a more specific owner group for the changed service directory.

Verification performed

For each pull request:

1. The approving review commit ID exactly matches the current PR head SHA.
2. The reviewer currently has active membership in at least one team required by the matching CODEOWNERS rule.
3. The PR is open, non-draft, clean, and independently shown as approved.

The approval reviewers differ between layers, but every layer has its own valid and current CODEOWNER approval.

Failure

Running the atomic merge produces:

merge failed: protected branch default-branch check failed:
  Waiting on code owner review from <required CODEOWNER users/teams>.

The reported owners correspond to the repository CODEOWNERS rules, but valid approvals from members of those teams are already present.

Environment

gh stack version 0.1.0
gh version 2.100.0 (2026-09-03)

Expected behavior

The stack should merge atomically because every layer satisfies the base branch review and CODEOWNER requirements, or the error should identify the specific PR/review that the asynchronous stack merge API considers invalid.

Actual behavior

Atomic stack merge rejects the entire stack with a generic missing CODEOWNER approval message, while the normal PR API reports every PR as clean and approved.