Collab event emitted when a collab session closes.
@type t() :: %Codex.Events.CollabCloseEnd{ call_id: String.t() | nil, receiver_agent_nickname: String.t() | nil, receiver_agent_role: String.t() | nil, receiver_thread_id: String.t() | nil, sender_thread_id: String.t() | nil, status: Codex.Protocol.CollabAgentState.t() | nil }