Workflow (saga) timeouts #259

Context

Timeouts are the most common saga need: "if payment isn't received in 24h, cancel the order".

Messages sent from a workflow handler already carry stickyAttributes.workflowId, and the default when lookup maps it back to $workflowId. So once #258 lands, a delayed send from a workflow handler is already a timeout routed to its instance.

The gap is noise. A message for a completed workflow logs No existing workflow state found for message. Ignoring. at error level in WorkflowRegistry, and a timeout would trip that routinely.

Decisions

Answered by the maintainer:

1. No timeout API. A timeout is ctx.send(new PaymentTimedOut(...), { deliverAfter }), handled with .when(PaymentTimedOut, ...). It's an ordinary message, type-checked by the existing workflow mapper checks.

Proposed:

2. A message whose workflow instance has completed or been discarded is dropped and logged at debug. On a miss, the registry re-queries with includeCompleted to tell "completed" apart from "never existed". "Never existed" stays a warning or error.
3. There's no cancellation: the timeout handler checks the state and ignores itself if the step already happened.
4. Time control in tests is Handler and workflow test helpers #265's job: its workflow scenario runner records delayed sends and delivers them with advanceTime.

Non-goals

• Cancelling a timeout.
• A timeout-specific mapper method or a requestTimeout helper.
• Fake clocks.

Approach

• WorkflowRegistry: the miss handling described in decision 2. No new persistence methods; getWorkflowState(..., includeCompleted) already exists in every persistence.
• Integration tests in bus-core for class workflows and defineWorkflow workflows, using the in-memory transport.
• Docs page /guide/workflows/timeouts with snippets for both workflow styles.

Acceptance criteria

• A delayed send from a workflow handler is handled by that workflow instance only
• A timeout that arrives after the workflow completed is ignored, logged at debug, not error
• Tests for class and function workflows
• Docs page and snippets; changeset