Uniform context-in/context-out interface for workflow participants.

Every participant in a composition — actions, agents, nested workflows — implements this behaviour. Nodes form an endomorphism monoid over context maps, composed via Kleisli arrows.

Return Types

• {:ok, context} — success with implicit outcome :ok
• {:ok, context, outcome} — success with explicit outcome for FSM transitions
• {:error, reason} — failure with implicit outcome :error

Directive Generation

The to_directive/3 callback allows strategies to dispatch nodes polymorphically without pattern-matching on concrete struct types. Each node knows how to produce the appropriate directive(s) for execution given a flat context and keyword opts.

Opts carry strategy-specific metadata (e.g. :result_action, :tag, :meta) so the node remains strategy-agnostic.

The to_tool_spec/1 callback lets nodes describe themselves as LLM tool definitions for orchestrator contexts. Nodes that cannot act as tools return nil.