refactor(agent): add wait_for_agent tool and simplify prompt sending API

AGENTS.md

@@ -1,48 +0,0 @@
-# Agent Lifecycle
-
-This project uses client-driven lazy initialization for Claude Code agents. Sessions start without spinning up agent runtimes; the client opts in when needed.
-
-## Connection Bootstrapping
-- The session emits `session_state` after connection with an array of agents. Each entry matches the server `AgentInfo` structure (`id`, `status`, `createdAt`, `type`, `sessionId`, `error`, `currentModeId`, `availableModes`, `title`, `cwd`).
-- No history or runtime is loaded at this point. Every agent starts in `uninitialized` and only streams live status updates once subscribed.
-
-## Opting In To An Agent
-1. When the UI needs an agent, send an inbound session message:
-
-   ```json
-   {
-     "type": "initialize_agent_request",
-     "agentId": "<agent-id>",
-     "requestId": "<optional-correlation-id>"
-   }
-   ```
-
-2. The session subscribes to the agent, calls `AgentManager.initializeAgentAndGetHistory`, and lazily starts the runtime if required.
-3. The server responds with:
-
-   ```json
-   {
-     "type": "agent_initialized",
-     "payload": {
-       "agentId": "<agent-id>",
-       "info": { /* same shape as session_state agents */ },
-       "updates": [
-         {
-           "agentId": "<agent-id>",
-           "timestamp": "2024-01-01T00:00:00.000Z",
-           "notification": { /* AgentNotification */ }
-         }
-       ],
-       "requestId": "<optional-correlation-id>"
-     }
-   }
-   ```
-
-4. After the response, all ongoing traffic uses the existing channels:
-   - `agent_status` continues to broadcast status changes.
-   - `agent_update` streams real-time session notifications, permission prompts, etc.
-
-## Notes
-- `initialize_agent_request` is idempotent. The manager short-circuits if the agent is already ready and returns the cached history.
-- Session state no longer replays history when clients reconnect; clients must explicitly reinitialize agents they care about.
-- `requestId` lets the caller correlate UI state but remains optional throughout the flow.