Status: IN
The four sender-receiver decoupling patterns (Command, Observer, Mediator, Chain of Responsibility) all achieve decoupling through object composition rather than inheritance, confirming that behavioral flexibility in communication requires composition as its assembly mechanism — each pattern reifies a different communication topology (request, broadcast, hub, chain) as a composed object.
The decoupling topology (depth-1) is enabled by composition preference (depth-1) — topology and mechanism unify
Depends on (SL): four-decoupling-patterns-topology, behavioral-patterns-favor-composition