skills: t27o -- day-two lessons and the tri pr preflight gate (measure first, emitter fixes re-seal, lane cleanup scope, items vs fns) #11209

Goal

Put the lessons of 2026-10-19/20 (day two of the t27o loop) into the t27o skill, and point its review checklist at the command that now runs it: tri pr preflight --quick (landed in #11207, 13 rules, exit 0, 1 or 2).

Why

The skill's review step still lists the checks by hand; since #11207 one command runs the seal, vacuity, types, dupes, ledger, census, own-language budget and home-path rules. The day also produced lessons that cost hours and are not in the skill: measure before writing a rule (two rules were not written, saving two pull requests: #11135, #11145); an emitter fix moves every spec whose output it changes, so check_seal_currency.py and check_seal_coverage.py must run locally (#11192 lost an hour to 16 stale seals); a lane's cleanup glob wiped other lanes' files in the shared scratchpad; items and fns are different denominators (6,180 items over 16,057 fns was reported as a 38.5% share, the fns-only figure is 30.8%); free disk follows swap and load, not files; PR-body edits re-queue the required check-linked-issue.

Boundary

• .claude/skills/t27o/SKILL.md

User Scenarios

• Given a lane about to push, when it reads the skill, then it runs tri pr preflight --quick and the two seal checks if it changed an emitter or a spec.
• Given a proposed converter rule, when the skill is read, then it says to measure first and to write the rule only above a stated threshold.
• Given a lane's cleanup step, when the skill is read, then it names only its own scratch directory.

Requirements

• FR-001: The skill MUST name tri pr preflight --quick as the local gate and say what it does not cover (the seal currency and coverage checks, the cargo tests).
• FR-002: The skill MUST keep one line per lesson, no copy of an issue body, and MUST NOT contain a developer home path (python3 -I tools/check_devhome_paths.py).
• FR-003: The change MUST be documentation only.

Success Criteria

• .claude/skills/t27o/SKILL.md gains at least 8 lines and fewer than 40, and python3 -I tools/check_devhome_paths.py ends with exit 0.
• The required checks of the pull request pass.