ci(review): replace the Merge Oncall with CODEOWNERS review routing

[BobbyZhouZijian]

Motivation

Implements accepted RFC #656. Every pull request was assigned to a single Merge Oncall, who also owned the default CODEOWNERS rule. Over the last 30 days that one account merged 156 of about 200 pull requests. This change routes review and merge responsibility by CODEOWNERS instead.

Changes

• Remove .github/merge-oncall.json, the assign merge oncall workflow, and the on-call validation in check_community_files.py.
• CODEOWNERS: every area lists a primary and a backup owner, and one approval from either is enough. The default * rule is owned by @BobbyZhouZijian and @quao627, and general /docs/ by @BobbyZhouZijian and @Benjamin-eecs.
• MAINTAINER.md: replace the Merge Oncall role with Code owner and add a Review routing section.
  • An author with write access merges their own pull request after one approval.
  • An approving code owner merges external contributions.
• Add review-reminders.yml. It runs daily, but only posts on every third UTC day, and can be triggered manually at any time. When it posts, it comments on a fixed [Task] Pull request review reminders issue with ready pull requests that have had no activity for three days, and mentions who each one is waiting on:
  • the requested reviewers, or the author if no reviewer is requested;
  • the author, when changes are requested;
  • once approved, the author if they have write access, otherwise the approving reviewers.
• Update the on-call wording in the PR template and CONTRIBUTING.md.

Compatibility and operational impact

• New pull requests are no longer auto-assigned or commented on at open time.
• Open pull requests were already reassigned manually to match the new rules.
• There are no changes to product APIs or persisted data.
• Optional follow-up for an admin: set required_approving_review_count to 1 in protect-main to enforce the one-approval rule.
• The reminder is one short scheduled job per day, and it exits early on days it does not post.

Verification

• pre-commit run --files <changed files> passed.
• python .github/scripts/check_community_files.py reported Community configuration is valid.
• The reminder script was dry-run against the live repository with the GitHub issue API calls replaced by local stubs. It classified four idle pull requests (feat: MLX training backend for Apple Silicon + OpenClaw-RL end to end #325, feat: add adaptive KL controller contracts #597, feat: integrate adaptive KL with training lifecycle #598, feat: add PPO RLHF adaptive KL recipe #599) as waiting for review, mentioning the expected reviewers.
• actionlint was not run locally. CI runs it.

AI assistance

Claude Code drafted the workflow, CODEOWNERS backup assignments (based on recent contribution history), documentation changes, and the RFC. I reviewed the changes and the resulting behavior.

Checklist

• The change is focused and contains no unrelated cleanup.
• Changed code satisfies the style, code structure, and naming rules in AGENTS.md.
• Tests cover behavior changes, or this pull request does not change behavior.
• Public interface changes include contract tests, or no public interface changes are present.
• Affected user and developer documentation is updated, or no documentation update is required.
• Root README changes update both languages and README.i18n.yaml, or do not affect README content.
• An accepted RFC is linked, or this change does not require an RFC.
• Relevant pre-commit and test checks pass.
• Non-trivial AI assistance is disclosed above, or none was used.

Review and merge

Reviewers are requested automatically from CODEOWNERS. See the
maintenance model
for review and merge requirements.

🤖 Generated with Claude Code

[github-actions]

Merge Oncall: @BobbyZhouZijian

The merge oncall will route reviews and keep this pull request moving toward a clear decision.