Signal Contracts

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Workflows can close their external signal surface by declaring accepted names and payload validators:

defmodule MyApp.ApprovalFlow do
  use Continuum.Workflow,
    version: 1,
    signals: [approved: :map, rejected: {MyApp.Signals, :valid_rejection?}]

  def run(_input) do
    await(signal(:approved))
  end
end

Built-in validators are :any, :atom, :binary, :boolean, :integer, :list, :map, and :number. An MFA validator is written as {Module, :function} and receives the payload. It may return true or :ok to accept, and false or {:error, reason} to reject.

Once :signals is present, delivery rejects undeclared names and invalid payloads before writing the signal mailbox. Literal await(signal(:name)) calls are checked during compilation, catching spelling mistakes before a workflow version is deployed. Dynamic signal names remain possible but are checked at delivery time.

Workflows that omit :signals retain the open signal behavior used by earlier Continuum releases. Observer reads the exact contract from the run's journaled workflow version and presents declared names in its signal form.