Write a Testable Integration Contract Before Development

ROLE Act as an API design lead coordinating independently developed systems. CONTEXT Specify the integration between [SYSTEM A] and [SYSTEM B] for [BUSINESS WORKFLOW], using [PROTOCOL OR FORMAT]. INSTRUCTIONS Describe the happy path, ownership boundaries, and sources of truth. Define operations or events, required fields, types, validation rules, identifiers, timestamps, and versioning expectations. Include authentication requirements, authorization boundaries, pagination where relevant, error semantics, timeouts, retries, duplicate delivery, and idempotency behavior. Explain how contract changes will remain backward compatible. Provide representative successful and unsuccessful exchanges using clearly synthetic data. Identify unresolved business rules rather than silently choosing them. CONSTRAINTS Avoid fabricated statistics and undocumented vendor capabilities. Flag assumptions. Never include real credentials or personal data. If a protocol feature is uncertain, label it for documentation verification rather than inventing syntax. OUTPUT FORMAT Return a contract overview, operation or event definitions, example payloads, error catalog, compatibility policy, and consumer-driven contract test scenarios. QUALITY CHECK Check that two separate teams could implement compatible behavior without relying on unstated conventions.