Choose an owner

Choose one execution owner before choosing a notification bridge.

Requirement	Use	Lifecycle responsibility
An existing framework or domain layer manages execution	OperationState<T> directly	Existing owner guards success, failure, cancellation, and disposal
Multiple operations or configurable concurrency	AsyncOperation<T> fields	Dispose each engine
One request on a store, Cubit, service, or controller	AsyncOperationMixin<T>	Publish changes and call disposeOperation()
One widget owns a request	AsyncOperationStateMixin<T, Widget>	Adapter owns initialization and disposal
Host owns repeated events	StreamOperation<T>	Await cancellation/disposal
One stream on an external host	StreamOperationMixin<T>	Publish changes and await disposeOperation()
One widget owns repeated events	StreamOperationStateMixin<T, Widget>	Adapter owns startup and routes cleanup failures
Reusable specialized behavior	Extend an operation	Subclass preserves engine contract
Host receives a specialized engine	Override operationController	Injection transfers disposal ownership

A state manager does not automatically make direct state the best choice. If direct state would require writing a new generation counter, disposal guards, and stale-error handling, compose an operation instead.

Framework state exposes snapshots published by the operation. Keep the operation as the execution owner rather than updating those snapshots independently. Use a separate engine for each independent request or subscription. A host mixin represents one operation.

Choose the payload from success semantics

Type	Meaning of success
User	A user is required
User?	A successful lookup may return no user
void	Completion is the meaningful result

Do not use an arbitrary nullable payload to represent a command. Do not infer success from hasData. Nullable lookups and commands can succeed without data.

When a larger state machine is needed

Use domain orchestration for atomic coordination, offline sync, retries, queues, or states beyond idle/loading/success/error. Operations can remain fields inside that model. They do not replace domain invariants.