Verification and tests

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Test observable guarantees

input → behavior → output

Find existing tests before changing behavior. Update the contract and add genuinely new scenarios. Do not delete tests because they resist a refactoring, and do not reproduce implementation details in assertions.

Check domain errors, ownership boundaries, optimistic conflicts and user-visible recovery. Keep API mocks close to the real contract and use domain-specific builders for readable scenarios.

Run relevant type checks, lint, tests, build and runtime checks. Inspect the final diff for unrelated formatting, changed public APIs and ownership leakage. Report checks that could not run; a successful build alone does not establish correct behavior.