1. The $217 Overnight Code Review

Reconstruction for teaching. Fictional org (Meridian/payments-gateway), synthetic data; the receipts are generated, not from a real run. The dollar figures (including the $217 in the title) are illustrative — as of June 2026, verify before relying.

Pattern: circuit-breaker + cost cap · Primitive: /loop · Domain: coding

Use when

You want an agent to review an open-PR queue continuously, overnight or between standups — without it re-reviewing unchanged PRs forever and billing you for the privilege.

The loop (copy-paste)

This is the library card for this example. Copy the contract and fill the brackets:

Goal:        Review every open PR in <repo> once per changed revision.
Context:     <repo> at HEAD; the open-PR queue and each PR's head SHA.
Constraints: Read-only. One comment per PR per changed SHA. Hard cap <$N>/night.
Done-when:   No PR has changed head SHA since the last pass.
Evidence:    A per-pass diff of PR head SHAs; a posted-comments ledger.
If-blocked:  Halt after 3 consecutive no-progress passes; never exceed the cost cap.

Verify

A separate check compares each PR's head SHA to the prior pass. If none changed, the done-condition holds and the loop halts. The comments ledger must show at most one comment per PR per SHA.

Steps

Snapshot the PR queue and head SHAs.
Review only PRs whose SHA changed since the last pass.
Record cost + SHAs; halt on 3 no-progress passes or at the cap.

What happened

Run unattended overnight, the ungoverned loop re-reviewed the same 12-PR queue 91 times and billed $217.34 — 87 of those passes found nothing new, just re-read an unchanged queue every ~5 minutes. The governed version (Done-when: no PR changed; halt after 3 no-progress passes; a $15/night cap) did the same job in 4 passes for $11.20. (Illustrative — as of June 2026, verify before relying.)

Cumulative cost: ungoverned vs governed

The receipts

Loop log (91 passes) — no_new_work=true from pass 5 on.
Ungoverned cost ledger and governed cost ledger.
Comments posted — one PR, 91 near-identical bot comments.
The governed loop contract · all artifacts.

Notes

The fix isn't a smarter model — it's a Done-when the model can't argue with (no PR changed) plus a circuit-breaker (3 no-progress passes) and a cost cap. Govern before you leave it running.