Primitives

Foundational domain objects that show up in three or more services. If you are reasoning about behaviour at the service level, the primitives are the nouns; the services are the verbs.

Primitive	Where it shows up
Workflow execution	History (state), Frontend (API), Matching (tasks), Worker (system workflows).
History event	History (event sourcing), Replication (delivery unit), SDK (event playback).
Mutable state	History (in-memory + persisted), Replication (verification target).
History task	History (transfer/timer/visibility/outbound/replication/archival queues).
Task queue	Matching (owner), Frontend (poll endpoint), History (target of Transfer Tasks).
Namespace	Every service. Isolation boundary, retention, archival, replication scope.
Shard	History (unit of horizontal scaling), Membership (assignment), Replication (stream pinning).

These pages are short — each is a single concept. Use them as a glossary that links into the deeper service / system pages.