Sprint Contract

The evaluator's leverage collapses when "done" is defined after the code exists. The generator ships something, the evaluator finds it plausible, the fuzzy spec silently reshapes to match what got built. Premature victory, dressed up.

Fix the timing: write the contract before the generator writes a line of code. The evaluator's job for the sprint is then mechanical — hold the artifact against the contract, no re-negotiation mid-flight.

Inspired by the planner/generator/evaluator split in Prithvi's March 2026 post on multi-agent harnesses.

When to apply

• You're about to start a chunk of work (one feature, one refactor, one bug fix) with an evaluator or reviewer persona in the loop.
• The planner output or upstream spec is ambiguous — you can imagine two reasonable implementations that both "satisfy" it.
• A session just rehydrated from shift-notes / a progress file and needs a concrete acceptance target before it picks up the keyboard.

Procedure

1. Name the one deliverable. One feature, one sentence, user-observable. If you can't say it in a sentence, the sprint is too big — split it, contract the first slice.
2. Write the acceptance predicates. 3-7 bullets, each one a check that either passes or fails. No "clean code", no "good UX" — write predicates a script or a browser click can decide.
3. Name the runtime path. How is this exercised end-to-end? Which URL, which CLI invocation, which button click? The evaluator will drive this exact path — no substitutes.
4. List the out-of-scope items. Two or three things the generator will be tempted to also fix. Written down = evaluator will reject them as scope creep, generator has an anchor when tempted.
5. Sign it in the shift notes. Paste the contract into claude-progress.txt (or equivalent) under a ## Sprint contract header, with the sprint start timestamp. Both personas reference this exact text for the rest of the sprint.
6. Then, and only then, write code.

Contract shape

## Sprint contract — <ISO timestamp>

Deliverable: <one sentence, user-observable>

Acceptance predicates:
- [ ] <predicate 1 — script-decidable>
- [ ] <predicate 2>
- [ ] <predicate 3>

Runtime path: <exact URL / CLI / click sequence the evaluator will drive>

Out of scope this sprint:
- <tempting adjacent fix>
- <tempting refactor>

Anti-patterns

• Predicates that are prose, not checks. "Handles errors gracefully" is not a predicate. "Returns 400 with {error: "missing_field"} when name is absent" is.
• Renegotiating mid-sprint. If the generator hits a wall, it does not edit the contract to route around it. It surfaces the wall, the planner revises scope, a new contract gets signed. Evaluator leniency comes from mid-flight edits — block them structurally.
• Contract written by the generator alone. The generator will write predicates its planned code happens to satisfy. Have the evaluator draft or at least sign off before code starts.
• No runtime path. Without it, the evaluator falls back to reading unit tests — see [[broken-window-check]] for how that fails.
• Skipping the out-of-scope list. This is the cheapest anti-drift device you have. Skip it and you'll ship a "small refactor" that broke two other features.

Rehydration case

Fresh session, no memory of the previous one. Read shift-notes, find the last signed contract with unchecked predicates. That is your target — no re-planning, no reinterpretation. Drive the runtime path, tick the predicates, ship. If the contract looks wrong on inspection, do not edit it; revert to the planner, get a new one signed.

Cost

Two to five minutes of prose before code. In return: the evaluator has something to be strict about, the generator has an anchor against scope drift, and the next session inherits a testable target instead of a vibe.

Related

• [[shift-notes]] — where the contract lives across sessions.
• [[broken-window-check]] — what the evaluator runs against the contract at session start.
• [[adversarial-verify]] — the end-of-sprint pass that decides whether every predicate actually holds.

When NOT to apply

Trivial edits (typo fix, one-line config change, dependency bump) — the contract overhead exceeds the work. Solo runs with no evaluator persona in the loop — write yourself a one-line acceptance note instead and move on.