Trace Story

A typical browser-to-actor method call produces a connected trace across client, transport, actor, and event handling.

Browser to actor

1. The browser calls client.fn("Move")(...).
2. Client.fn creates a client span.
3. The client encodes that span into F.Payload.trace.
4. The Durable Object receives the WebSocket message and creates a socket-message transport span.
5. The actor handler span is parented to F.Payload.trace and linked to the local transport span.
6. If the handler emits an event, event.send creates a producer span and attaches Event.trace.
7. The browser receives the event and creates an event.enqueue consumer span parented to Event.trace.
8. The response listener resolves the original call under the stored client span. There is no separate response span.

event.enqueue covers Liminal publishing the event into the client's internal PubSub. It does not implicitly parent arbitrary Client.events stream consumers; app-level event processing should create its own spans if that distinction matters.

HTTP upgrade

The HTTP upgrade path also participates:

1. Worker.fetch extracts incoming traceparent or B3 headers and creates a server span.
2. WorkerdActorNamespace.upgrade runs under that span.
3. The namespace forwards trace headers to stub.fetch.
4. The actor runtime fetch callback extracts those headers inside the Durable Object and creates the Durable Object-side server span. It also creates the socket session id and persists the session trace in the WebSocket attachment.

Read Propagation for the trace envelope details.