Add event emitter for subscriptions#864
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Subscribers can now emit events back into the store by type-hinting an EventEmitter argument on a subscribe method. Emitted events go into a dedicated subscription_<id> stream by default, or an explicit stream via linkTo, so other subscriptions can react to them. By default events are only emitted during run; while booting the emitter is a noop to avoid duplicates on replay. This can be overridden per subscriber with the OverrideEventEmitting attribute. When a subscription is removed an OnSubscriptionRemoved event is dispatched; registering the RemoveSubscriptionStreamListener removes the subscription stream from the store. ArgumentResolver::resolve() now receives an ArgumentResolverContext (message, subscription and subscriber metadata) instead of just the message. See UPGRADE-4.0.
The default stream name (subscription_<id>) is now built directly in the EventEmitterResolver and the RemoveSubscriptionStreamListener. Also rename the DefaultEventEmitter property to defaultStream.
DanielBadura
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LGTM besides naming stuff, but we need some more unit tests as even the non-diff mutation test is failing
Replace the OverrideEventEmitting(bool) attribute with two dedicated marker attributes: EnableEventEmittingDuringBoot (also emit while booting) and DisableEventEmitting (never emit). The subscriber metadata now carries two booleans instead of a nullable one.
The handler tests now record dispatched OnSubscriptionRemoved events and assert them for every removal path (and assert none on the teardown error/no-removal paths). The resolver test now emits through the resolved emitter and asserts the subscription_<id> target stream, instead of only checking the returned type.
Add a MessageProcessorTest that drives a real subscribe method through the processor (covers the previously uncovered foreach), assert StoreEventEmitter does not touch the store for empty event lists (mock instead of in-memory, to kill the return-removal mutant), and add a two-subscription teardown test so the continue after a cleanup error is not equivalent to a break. Also assert the SubscriberMetadata event-emitting defaults.
DanielBadura
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Jun 16, 2026
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Subscribers can emit events back into the store. If a subscribe method type-hints an
EventEmitter, it gets injected and the subscriber canemit()events into its ownsubscription_<id>stream, orlinkTo()an explicit stream. Another subscription can then subscribe to those events. Typical use case: a projection finishes updating and emits an event that a notification subscriber reacts to.Emitting only happens during
runby default; while booting the emitter is a noop so a replay doesn't duplicate events.#[OverrideEventEmitting(true)]also emits during boot,falsesuppresses it entirely.When a subscription is removed the handlers dispatch
OnSubscriptionRemoved. Registering theRemoveSubscriptionStreamListeneron the event dispatcher removes the correspondingsubscription_<id>stream from the store.