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lesson: a merge-method change requires a synthetic 3-commit PR through the merge queue first #5857
Description
Operator 12:14Z (relayed by aprender-57, item 4): a merge-method change (squash / merge commit / rebase) must first be exercised by a synthetic 3-commit PR taken through the merge queue.
Why: the history-shape sweep (handoff/wsweep-mergebase-sweep-1214.md) found 22 high-risk assumptions of one-commit-per-PR / single-parent heads (resolve_base.sh, ci_test_tier.sh, ci_mg_reuse.sh K1/K2/P2, check_pr_review_arm4.sh, review_receipts_nightly.sh, hardcoded --squash). Under rebase several under-select silently; under merge commits Arm 4 and the nightly receipt check go RED.
Acceptance: (1) a script or runbook step opens a throwaway 3-commit PR, enqueues it, and asserts every merge-path guard stays green with the same verdicts as a squash; (2) the method change is blocked until that receipt exists; (3) falsifier: re-introducing a HEAD^1-only diff makes the synthetic PR go RED.
Owner: wsweep to file; implementation owner TBD by the cop. Branch/PR only; a gate change needs quorum + 2 non-author seats.
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Activity
noahgift commentedon Oct 21, 2026
Second lesson (operator 12:26Z item 4, relayed by aprender-57): a new runner group must pass a canary job before it counts as live.
Cause (2026-10-21): runner group 14 was created with allows_public_repositories=false, so aprender jobs could not land on it for ~4 min.
Acceptance: (1) creating or changing a runner group runs a canary job from each repo that is meant to use it (public and private) and asserts it lands on a runner of that group; (2) a group does not count as live (no capacity, no routing) until its canary is green; (3) falsifier: a group with allows_public_repositories=false fails the aprender canary.
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noahgift commentedon Oct 22, 2026
Tracked in #5510 (triage 2026-10-22).
noahgift commentedon Oct 22, 2026
tracked in #5962