Correct

Assume the next contributor is an agent that sees only the files it opened, copies the nearest example, and takes the shortest path that compiles. A rule it has to remember fails; a check that fails its build doesn't.

On every correction

1. Fix the instance.
2. Look it up in the repo's rule table (AGENTS.md, "Rules and their checks"). Then search for earlier cases: git log -S/--grep, review threads (gh api repos/<o>/<r>/pulls/comments), past cross-review and verify findings.
3. First time: add a row with Check: none yet and the PR or message that showed it. The row is how the second time gets noticed.
4. Second time (a row already there, or an earlier case found): build the check now, in this change or the next PR.

Pick the highest check that catches it

1. Type: make the bad state impossible to write. When the mistake comes from two ways of doing one thing, delete one; then there is nothing to get wrong.
2. Lint or CI check whose message names the fix: "use formatTime() from shared/time.ts, not toLocaleTimeString", not "invalid time format". If the pattern is already common, fail only on lines a change adds.
3. Test of the behaviour, through the test-audit gate.
4. Verifier rule: for what only a render or a run shows (off-centre, clipped, wrong in one locale), a rule in the repo's verify-<app> skill that says what to measure and the tolerance.
5. Doc: an AGENTS.md line, only for a judgment call no check can make. Nothing fails when an agent skips it.

Prove it

Run the check on the real past mistake: check out the bad commit in a scratch worktree, or reapply its diff, and paste the failing output. Then run it on the fix and show it pass. The same command runs locally and in CI.

The table

## Rules and their checks

| Rule | Check | Seen in |
|---|---|---|
| App icon centred against its peers | verify-android rule "icon centre" | #41, #57 |
| UI strings carry no AI tells | `pnpm lint:copy` | #63 |
| A Settings subtitle only when the title can't stand alone | none yet | #70 |

A row whose check is "none yet" and that is seen again is a repeat: build the check in the same change. Drop a row once its mistake can't happen.

Gotchas

• A message that names no fix gets the check suppressed or worked around by the next agent.
• Proving on an example you made up misses what the real mistake looked like (a regex that catches your example and not the past diff).
• A doc-level fix when a check was possible is how the same correction comes a third time.
• Exceptions go on the offending line, with the reason.
• A broad exemption (a whole directory) turns the check off. Fail only on new lines instead.
• One check per commit, naming the correction it encodes, so a revert is clean.