Optional protocol for nodes that need post-fold coordination.

After apply_event/2 has folded a runnable's events into the workflow, some node types need to inspect the updated graph to determine if a coordination step is complete (e.g. all Join branches satisfied, all FanIn items collected).

Nodes that implement this protocol will have finalize/3 called during apply_runnable/2. The callback receives the node, the current workflow (with events already folded), and the original runnable. It returns {workflow, derived_events} where derived_events have been folded into the returned workflow.

Nodes that do not implement this protocol are assumed to need no coordination — apply_runnable/2 skips the coordination step for them.

Built-in Implementations

• Runic.Workflow.Join — rechecks branch satisfaction after folding JoinFactReceived events, emits JoinCompleted + JoinEdgeRelabeled events when all branches are satisfied.

• Runic.Workflow.FanIn — rechecks whether all fan-out items have been processed, emits FanInCompleted + sister ActivationConsumed events when ready.

Example

defimpl Runic.Workflow.Coordinator, for: MyApp.CustomCoordinationNode do
  def finalize(node, workflow, runnable) do
    # Check coordination condition, emit derived events if complete
    {workflow, []}
  end
end