Overview

The stable, public contract — operations, reads, and events — that clients consume. Implemented as per-domain microservices behind load balancers; the surface a tenant sees reflects its variant (which endpoints exist) plus its extensions (additional or overridden behavior).

Layer 4 reflects Layer 3 (what's allowed), not Layer 2 (what's possible), and is conservative by design — once exposed, endpoints age forever.

The full API surface, versioning policy, and per-domain endpoint design will live under this section.