Interaction sessions

createInteractionSession coordinates portable conversation state around an explicit AgentRunner. The host supplies:

• a conversation identity;
• a prepared agent definition;
• the concrete runner integration;
• a reservation-capable ConversationStore;
• identity allocation; and
• an execution-event sink.

The reservation occurs before runner execution. This prevents a post-execution optimistic conflict from making a consequential effect safe to repeat.

There is no convenience createConversation that selects a hidden local runner. Applications may wrap InteractionSession in their own product API without widening the kernel.