system-interface-contracts

An interface contract makes system-to-system boundaries explicit by defining producer and consumer ownership, inputs, outputs, and invariants, which prevents modules from breaking each other during evolution.

You define deterministic behavior rules for API boundaries by specifying explicit error handling, timeout, retry, and idempotency or deduplication expectations within the interface contract to ensure producers and consumers remain aligned.

Version API changes safely by separating additive modifications from breaking changes within the interface contract, setting clear deprecation expectations and compatibility rules so existing consumers can adapt without failures.

Contract tests for system boundaries should include verification criteria and fixtures covering both positive and negative cases, ensuring that required fields, forbidden states, and observability expectations are consistently honored.

You need to write an interface contract before multiple modules, services, or agents implement different sides of the same boundary, ensuring that ownership, invariants, and deterministic behavior are explicitly agreed upon.

Yes, defining system boundaries requires specifying forbidden states alongside required and optional fields to establish clear invariants, ensuring that modules can evolve safely without violating expected interface behavior.