API Compatibility Time Machine

 Build an API compatibility analyzer that compares multiple versions of an API specification, implementation, or captured test fixtures. Detect removed endpoints, renamed fields, changed types, stricter validation, altered defaults, authentication changes, and response differences that could break existing clients. Generate a compatibility timeline, affected-client matrix, migration guidance, and automated contract tests. Classify each finding as confirmed breaking, potentially breaking, or informational, and explain the evidence supporting that classification.