Conversation control

A conversation is more than messages. The company can ask the user to sign in part-way through, the user can talk to the company directly through the agent's interface, either side can bring in a person, and the agent can close it. The paired examples drive one Manzanita conversation through all four, against a Manzanita with a support desk staffed.

Sign-in mid-conversation (§7.11). An authorization event says what is missing (sign_in_required or insufficient_scope) and which scopes. The host signs in with any mode the company offers and keeps sending to the same conversation ID with the new token.
Direct Conversations (§7.10). Only the personal agent starts one, for the user to talk with the company in the agent's interface. While it is open, the parent refuses messages and handoff with direct_conversation_open; the SDK puts the open conversation's ID in error.details["conversation_id"].
Handoff (§7.9). handoff() asks for a person; the conversation is queued until one takes it, then responder is human. When no one is available the company says so and the agent continues.
Closing (§7.12). close() ends the conversation; operations it proposed or started are not cancelled.

The model sees event types, statuses, the company's answers, and error codes. Tokens, the device code, and proofs stay host-only; the user code is shown to the user by the host, not by the model.

TypeScript: startDirect(), handoff(), and close() on ConversationClient, with the same error codes and details.