• Status: Accepted (#481)
• Issue: #481 (part of #469)

Store implementations beyond the built-in in-memory and SQLite ones (PostgreSQL first, Redis later) are going to live in repositories of their own (#469). The only proof that a store honours its contract — an atomic lease takeover, fencing epochs, the child queue's claim order, one of two concurrent pause transitions — were the core's internal suites (tests/infrastructure/*.contract.test.ts over storeKinds). A store outside the core could not run them, so it could not show that it behaves as SQLite does, and the core's own stores and an external one could drift apart.

• The suites are published as @agboss/core/testing/contracts: one function per contract — the nine #265 / #333 / #398 / #401 repositories and LangGraph's BaseCheckpointSaver — taking a ContractTarget<TStore> (name, instance(seam), reset?(), close?(store)). An entry of its own with its API report; @agboss/core/testing does not re-export it, because it imports vitest's describe / it (vitest stays an optional peer).
• The core runs the same suites: tests/infrastructure/*.contract.test.ts call the published functions with two targets (inMemoryTarget, sqliteTarget); storeKinds is gone. What the in-memory and SQLite stores pass is exactly what an external store runs.
• The suite owns the clock (#265: stores take time from the framework's Clock): every case gets a new VirtualClock at 2026-01-05T09:00:00.000Z, shared by the case's two instances and moved only by the case — a store that reads the database's or the machine's time fails the time-based cases.
• Every case runs on two instances over one backing store: reset(), then instance() for instance-1 and instance-2, the case, close() for each built store; a case needing one instance uses the first. A failing reset() fails the case with its own error; the case's error wins over a failing close().
• Store rules only: cases that run a whole application (testWith, fixture applications) test the framework over a store, not the store, and stay in the core's own tests. The rules keep their names, so a failure in a store's repository reads as in the core; every suite ends with ping().
• Proof that a suite catches a broken store: the core runs fixture suites against deliberately broken stores in a nested vitest (startVitest), the only way to assert a failing suite without failing its own run.

• One more public entry and API report to keep; the case tables are the contracts' executable specification, and a change to one is a change of the published API's behaviour.
• A new store contract gets its published suite with it, or it cannot be implemented outside the core.
• The in-memory stores stay internal: an outside author tests their own implementation (or a public SQLite one), never a copy of the core's.