Module session 

Multi-turn session helper over TurnRuntime.

Conversation state model (canonical)

• Turn-local buffer: VecConversationState implements ConversationState for the synchronous sample/tool loop.
• Session source of truth (optional): ChatStateHandle is the multi-turn durable surface. Prefer Session::run_turn_on_handle when you need actor isolation, usage ledger, or checkpointing via machi_state::ChatPersistence.

Do not treat the two as parallel “equal” product APIs: handle is the session store; VecConversationState is the turn engine buffer.

Structs

Session

Thin multi-turn orchestrator (one agent, persistent conversation state).