Ax Event Runtime

Ax Event Runtime

Use this skill when an Ax program should react to notifications, webhooks, timers, queues, task completion, or application events.

Mental Model

source -> inbox -> route -> target -> stored run -> sink

Sources never call an Ax program directly. A route must explicitly choose observe, invalidate, wake, or resume. Only the last two invoke a model.

Minimal Pattern

const source = new AxPushEventSource('application');
const target = eventTarget('triage')
  .program(triageAgent)
  .ai(llm)
  .input((input) => input.field('incident', eventPath.data()))
  .sink({ id: 'result', write: saveResult })
  .build();

const events = eventRuntime({
  sources: [source],
  routes: [
    eventRoute('incident-created')
      .types('incident.created')
      .wake(target)
      .build(),
  ],
});

await events.start();
await source.publish({ event, identity, trust: 'authenticated' });

Rules

• Supply identity from authenticated adapter state, never from event data.
• Treat events without verified identity as anonymous and untrusted.
• Map event data into signature inputs; do not synthesize a user message.
• Use eventPath.data('field') and other segment-safe selectors. Do not use dotted JSONPath strings or repurpose s() as a mapping language.
• Use .project(path) only for same-name signature projection. Explicit .field() mappings override projection; missing or invalid signature inputs dead-letter before model invocation.
• Use eventInput().project(...).field(...) when a declarative mapping should be callback-free and reusable, then pass that plan to .input(), .wakeInput(), or .resumeInput().
• Callback mapInput is an escape hatch, not a validation bypass: its result is normalized to the program signature and mapper failures dead-letter before invocation.
• Use .wakeInput() and .resumeInput() when the two actions need different contracts. Neither action silently uses the other action's mapping.
• Use observe for progress/logs and invalidate for catalog changes.
• Use resume only with an owned continuation correlation key.
• Use createProgram(instance) for stateful multi-tenant Agents.
• Declare retrySafety: 'idempotent' only when stable delivery keys protect every possible side effect.
• Persist outputs before final sink delivery; redrive sink failures separately.
• Use debounceMs and coalesce: 'latest' only when replacing intermediate events is part of the route's declared policy.
• Observe source failures with onSourceError.
• The in-memory store is volatile and single-process.
• For cooperating Node processes on one local disk, use AxSQLiteEventStore from @ax-llm/ax-tools/event/sqlite with explicit retention and coordination: 'multi-worker'. Never recommend SQLite on a network filesystem.
• Close the runtime and caller-owned protocol clients explicitly.
• Fan out to several Agents with several matching routes, not a multi-target route. This preserves independent authorization, ordering, retries, and runs.

Continuation Pattern

eventContext.registerContinuation({
  correlation: [{ kind: 'task', value: taskId }],
  expiresAt,
});

Route progress to observe. Route input_required, completed, failed, or cancelled task events to resume when the owning program must run again.

MCP Adapter

Use ax-mcp for client construction, transports, authentication, catalogs, subscriptions, tasks, and MCP-specific security policy. This skill owns the generic inbox, routing, continuation, store, and sink behavior.

Use client.inspectCatalog() to discover server-owned tools, prompts, concrete resources, and URI templates from only the endpoint. Then use AxMCPEventSource({ client, resourceSubscriptions, identity, trust }) with an explicit none/all/URI/selector policy. Omitted policy subscribes to no resources. Templates are never expanded automatically. Managed sources diff catalog changes, restore current logical ownership on reconnect, and release only their own subscriptions on close. Identity must come from the application's authenticated client or token mapping; a bare MCP session is anonymous. Add ...axMCPEventRoutes({ client }) for catalog invalidation, progress/log observation, and task resume. Resource notifications never get an implicit wake route. See docs/MCP_SUBSCRIPTIONS.md.

UCP Adapter

Use AxUCPWebhookEventSource({ client, identity }) inside an application-owned HTTP handler, then call source.ingest(request). Verification of the signer profile, RFC 9421 signature, digest, freshness window, key rotation, and replay key completes before enqueue. Resolve tenant/account identity from application state after verification; do not copy identity from the business payload.

Generated Python, Java, C++, Go, and Rust packages expose the same Core-owned single-worker event state machine plus functioning inline lifecycle dispatch, continuations, state restoration, cancellation, persisted outputs, isolated sink redrive, signature-aware path/input/target/route builders, and host-owned source, sink, clock, and store boundaries. Generated targets use the host signature plus a typed invocation callback when no common object-safe program interface exists. Do not claim persistent multi-worker support from axevent.single-worker alone.

Generated runtimes do not create worker threads. publish() drains work due at clock.now(). Hosts use nextDueAt() to schedule runDue() for debounce, retry, and continuation expiry; redrive() is due immediately. Manual clocks make these transitions deterministic. Generated in-memory stores enforce 10,000 pending deliveries, 64 MiB queued data, 1 MiB per envelope, and a five-second publication wait.

Testing

Use AxManualEventClock, AxInMemoryEventStore, deterministic event IDs, and an output-capturing sink. Assert that unmatched or observe-only events never invoke the program, tenant scopes do not collide, outputs exist before sinks, and uncertain side effects become outcome_unknown.

Persistent store implementations must pass runAxEventStoreConformance(createStore, { clock }). A store must not advertise multi-worker capability without the conformance marker checked by runtime startup.