PromptPack RFC 0010 adds composition mode—a declarative step-graph orchestration for procedural LLM workflows alongside existing dialogue patterns

PromptPack specification extended with composition as a fourth orchestration mode on WorkflowState. Composition mode uses a directed graph of typed steps (prompt, agent, tool, branch, parallel) to handle procedural workflows like document analysis pipelines, data extraction batches, and meta-eval aggregation—flows that don't fit the conversational turn-by-turn state machine model.

Composition is exclusive per state: when a state sets orchestration: composition, the declarative step graph handles the state's full orchestration end-to-end, and the composition's output may map to on_event transitions or terminate the state. This preserves the workflow state machine (RFC 0005) as the universal orchestration primitive while adding a new value to the orchestration enum.

Backward compatible: existing packs using internal/external/hybrid orchestration with prompt_task are unaffected. The RFC does not replace or deprecate the workflow state machine or agent loop extension; it adds only a new conditional field (composition) on WorkflowState.