/**
 * Subscribes the active session to the backend's customer SSE stream so agent replies
 * pushed by support staff appear in the conversation in real time. No-op when
 * `config.agentStream` is not configured.
 *
 * The flow is:
 *   1. POST {apiBaseUrl}/api/public/chat-stream/init  → returns a session-bound token + stream URL
 *   2. Open EventSource on that URL
 *   3. For every `agentReply` event, append a deduped 'bot' message to the active session
 *
 * The browser handles reconnect automatically, sending `Last-Event-ID` so the backend can
 * replay anything missed during the gap.
 */
export declare function useAgentStream(): void;