skills: t27o -- the evening lessons (Sonnet for every role, merge when auto-merge refuses, t27b ledger rows, types-ratchet names, gate warning) #11022

Goal

Put what the 2026-10-19 evening of the t27o loop cost into the t27o skill, so the next cron tick does not pay for it again: the model rule (Sonnet 5.5 for every role, #10929), the merge route when auto-merge refuses, the t27b ledger ownership rule, the types-ratchet name trap, the inherited-red test against the merge base, three sandbox traps, and the warning that the issue-shape gate closed 128 issues wrongly (#11007).

Why

Each item was learned the slow way tonight and is not in the skill yet. The skill still says "Opus plans and reviews, Sonnet implements", which the owner replaced on 2026-10-19. Examples: PR #10999 needed a rename (a fixture type Gate clashed with crm-sellers) and a rebase before its types ratchet went green; enablePullRequestAutoMerge refused PR #11012 with "in unstable status" while only non-required checks were red; and 40 live issues sat closed for hours behind a gate that had judged a stale payload.

Boundary

• .claude/skills/t27o/SKILL.md

User Scenarios

• Given a new tick of the loop that reviews a t27b PR, when it reads the skill, then it knows to edit the ledger rows in that PR and to compare dupe findings with the merge base.
• Given a PR whose only reds are master's, when auto-merge is refused as unstable, then the skill names the sha-guarded merge call.
• Given an issue closed with the label shape-refused, when the loop meets it, then the skill says to run its current body through the gate's checker first.

Requirements

• FR-001: The skill MUST state that Sonnet 5.5 plans, implements and reviews, with Opus only after two failed attempts or on the owner's word.
• FR-002: The skill MUST name the merge route for the case where auto-merge is refused and the required checks are green.
• FR-003: The skill MUST NOT grow beyond what the tick needs: one line per lesson, no copy of an issue body.

Success Criteria

• .claude/skills/t27o/SKILL.md contains each of the eight lessons, and its diff stays under 15 lines.
• The required checks of the PR pass.