Evaluate alternatives to Mergify for PR automation

[LalatenduMohanty]

Context

Mergify's rebase action is deprecated for fork PRs after July 1, 2026, and its update action only supports merge commits. There is no clean way to auto-rebase PRs that are behind main without polluting history (see #1069).

This issue tracks evaluation of alternatives.

Current Mergify Usage

1. Auto-labeling — adds ci or mergify labels based on PR title/files
2. Auto-merge — merges PRs when all CI checks pass + 1 approval
3. Auto-update — keeps approved PRs up to date with main (broken — creates merge commits instead of rebasing)
4. Conflict notification — comments on PRs with merge conflicts

Note: e2e/mergify_lint.py validates that .mergify.yml check-success rules stay in sync with the GitHub Actions test matrix. Any migration must preserve or replace this validation.

Alternatives

1. Kodiak

• Free for open-source, configured via .kodiak.toml
• Supports clean rebase (no merge commits) and works with fork PRs
• Auto-merge with CI check requirements + approval
• No native auto-labeling (would need a separate GitHub Action)
• Would require replacing mergify_lint.py with equivalent validation against .kodiak.toml
• https://kodiakhq.com/

2. GitHub Actions composite (peter-evans/rebase + pascalgn/automerge-action + actions/labeler)

• Free, fully customizable
• Fork PR rebase requires "Allow edits by maintainers" on the fork
• More maintenance overhead, no unified interface
• Could keep using mergify_lint.py if check-success pattern is preserved in branch protection

3. GitHub native merge queue + branch protection

• Free, built into GitHub
• No continuous auto-rebase (only at merge time)
• Poor fork PR support
• No auto-labeling

4. Aviator MergeQueue

• Free for <15 devs, rebase only on paid plan ($12/user/month)
• Fork PR support unclear
• https://www.aviator.co/mergequeue

[dhellmann]

I think you're looking for Mergify's merge queue feature: https://docs.mergify.com/merge-queue/setup/

Red Hat is already a customer of Mergify for some cases, let's try to avoid changing vendors if we can.