Event topics

Plugins communicate through the typed event bus (fn-70): topics are declared with a schema, retention policy, and delivery mode, then emitted and subscribed via context.events:

• declareTopic(spec) — requires events.topic.declare
• emitTopic(name, payload) — requires events.emit
• subscribeTopic(name, handler) — requires events.subscribe
• replay(name, opts) — requires events.replay
• listTopics() — requires events.inspect

Delivery modes: atMostOnce, atLeastOnce (retry/backoff/dead-letter), and ordered (partitioned). See EventsAPI, TopicSpec, and EventEnvelope in the API Reference.

Topic naming: public core-plugin topics use the owning plugin’s prefix (e.g. actions.receipt.written, scheduler.job.cancelled, notifications.delivered). Topics prefixed _host.* are host-internal — third-party plugins cannot subscribe to them.

TODO — host topic catalog

The authoritative catalog of core-plugin event topics (300+ topics across the fn-70 … fn-101 core plugins, with per-topic payload schemas and retention policies) lives in the AppOS host repo and is not machine-readable from this SDK repo yet. This page will grow a generated topic table once the host exports its topic registry. Until then, use context.events.listTopics() at runtime to enumerate topics visible to your plugin.