Behaviour and struct builder for domain events.

An event represents something that happened in the system. Events are immutable facts — they are never rejected or retried.

Defining an event

defmodule MyApp.Tasks.Events.AssessmentCompleted do
  use Orkestra.Event

  field :task_id, :string, required: true
  field :expert_name, :string, required: true
  field :action_name, :string, required: true
  field :status, :string, required: true
  field :result, :map, default: %{}
  field :cost_usd, :float, default: 0.0
end

Emitting an event

{:ok, event} = AssessmentCompleted.new(%{
  task_id: "task_123",
  expert_name: "architect",
  action_name: "perform-assessment",
  status: "success",
  result: %{...}
})

# From a command (preserves correlation, sets causation)
{:ok, event} = AssessmentCompleted.from_command(command, %{
  task_id: "task_123",
  ...
})