Extension acceptance policy

Welcome:

• New backends/adapters that honor contracts and invariants.
• New comparison policies or audit/reporting extensions.
• Additional examples, docs, or tooling that reinforce contracts.

Not welcome:

• Extensions that bypass contracts (silent fallback, hidden randomness).
• New public entrypoints that duplicate existing verbs (execute, replay, compare, explain).
• Mutations during replay or compare paths.

Rules:

• Public API modules are fixed; extend via documented seams (adapters, policies), not by adding new surfaces.
• Any extension must document its invariants and add tests that enforce them.