H.11.4 Runtime Compatibility

Shared source does not guarantee compatibility among artifacts that run or are consumed at different times. Supported source and dependency contracts belong to H.5.3 Compatibility Contracts.

• Define compatibility for APIs, protocols, schemas, configuration, persisted data, clients, workers, and toolchains where revisions overlap.
• Test the skew produced by rolling deployments, external consumers, queued work, cached artifacts, and stored data.
• Record which break requires a migration window, coordinated release, consumer approval, or supported line.
• Use expand-contract execution when the real boundary cannot move atomically.
• Separate compatibility repair from source revert, artifact rollback, deployment rollback, and data recovery.