contract harness (EXPERIMENTAL)

If a contract carries example values, the contract is a test. This is the contract equivalent of tjs-lang's signature tests: the declaration proves itself by execution, and a declaration that feeds tests is load-bearing — it breaks visibly when it lies.

import { enableAgentInterface, exerciseContract } from 'tosijs'

const agent = enableAgentInterface({
  expose: { roots, contract, write: true },
})
const report = exerciseContract(agent)
// report.failed === 0, or report.trials says exactly what lied

Conventions read from each root's serialized contract (describe().contract):

• examples: [...] (standard JSON Schema keyword) — every example is WRITTEN through the real surface: it must be accepted, and it must round-trip (read() returns what was written — catching contracts the app itself violates, not just values the contract refuses).
• $counterexamples: [...] (our convention) — every one must be REFUSED by write(). A contract that never refuses anything isn't a contract; counterexamples prove the gate exists.

State is snapshotted per root and restored after each root's trials.

Future: richer exercise steps as custom properties (e.g. $exercise) written in AJS — serializable like the schema, executable like a test, sandboxable like neither Function nor eval. The contract file becomes the whole conformance suite, shippable over the wire.

EXPERIMENTAL. Ships alongside the agent surface; shapes may change.