git:20260907.c81549e to git:20260907.ebb8c27

---

name: principle-prove-it-works

description: "Apply after completing a task, before declaring done. Verify against the real artifact (run the feature, read the actual value, inspect the diff), not a proxy, self-report, or 'it compiles.'"

user-invocable: false

---

# Prove It Works

Verify every task output by checking the real thing directly. Do not infer from proxies, self-reports, or "it compiles."

**Why:** Unverified work has unknown correctness. Indirect verification (file mtimes, output freshness, agent self-reports, cached screenshots) feels cheaper than direct observation. Acting on a wrong inference costs far more than checking the source.

**Pattern:** After completing any task, ask: "how do I prove this actually works?"

Check the real thing, not a proxy:

- Check process liveness directly, not indirectly through derived state

- Read the actual value, not a cached or derived representation

- When verification fails, suspect the observation method before suspecting the system

Code and features:

1. Build it (necessary but not sufficient)

2. Run it and exercise the actual feature path

3. Check the full chain: does data flow from input to output?

4. For integrations, test the full communication path end-to-end

Verify the process as well as the outcome. A correct result can rest on a broken process, and a review that checks results passes it: a clause reconstructed from the user's paste instead of the durable record, a constraint honored by chance from a file never read. For each fact you relied on, name the record it came from and confirm that record is the one the project's rules point at.

Red is a colour, not a measurement. A failing check proves the instrument only when the failure content is the disagreement you predicted. An exception, an empty collection against a non-empty literal, and a real mismatch all print red, so quote the assertion's diff (`Extra items in the right set`), never the assertion (`assert {...} == {...}`). A convergence probe keys on behavior only the new artifact can produce, never an identity field the old one also emits; a same-SHA restart lets old code report the new commit SHA.

Delegation: trust artifacts, not self-reports.

## Script the check when you can