Extension Contracts

Extension Contracts specify how a domain evolves additively: what can be extended, how versions are managed, which dependencies are declared and how compatibility is preserved with common engines.

Additive Extension Stack

Extensions build on the base domain; they must not replace the common engines or mutate the base contract silently.

Version Compatibility Graph

Version evolution should make compatibility explicit.

Extension Contract Requirements

Component	Required declaration	Constraint
Extension scope	What new classes, predicates or constraints are added.	Must be additive and explicit.
Base compatibility	Target base version(s) and dependency assumptions.	Must not imply silent replacement of the base.
Versioning	Independent extension version and compatibility class.	Must support upgrade traceability.
Activation policy	Whether extension is optional, required or conditionally enabled.	Must preserve deterministic behavior.
Interoperability impact	Expected effects on traversal, evidence, state or APIs.	Must be documented before activation.

An extension contract is acceptable when it adds specialized capability while preserving the semantics and mechanics of the shared substrate. If it requires replacement of a common engine, it is not an extension contract; it is an architecture change.