diff --git a/ROADMAP.md b/ROADMAP.md
index 17f1eae..31e26e3 100644
--- a/ROADMAP.md
+++ b/ROADMAP.md
@@ -529,3 +529,36 @@ PhoneWork/
 - [ ] Host client reconnects → re-registered, messages flow again
 - [ ] Long CC task on node finishes → router forwards completion notification to Feishu
 - [ ] Wrong `ROUTER_SECRET` → connection rejected with 401
+
+---
+
+## M3 Implementation Notes (from M2 code review)
+
+Three concrete details discovered from reading the actual M2 code that must be handled
+during M3 implementation:
+
+### 1. `bot/commands.py` accesses node-local state directly
+
+The current `commands.py` calls `agent._active_conv`, `manager.list_sessions()`,
+`task_runner.list_tasks()`, `scheduler` — all of which move to the host client in M3.
+
+**Resolution:** At the router, `bot/commands.py` is reduced to two commands:
+`/nodes` and `/node <name>`. All other slash commands (`/new`, `/status`, `/close`,
+`/switch`, `/direct`, `/smart`, `/shell`, `/tasks`, `/remind`) are forwarded to the
+active node as-is — the node's mailboy handles them using its local `commands.py`.
+The node's command handler remains unchanged from M2.
+
+### 2. `chat_id` must be forwarded to the node
+
+`bot/handler.py` calls `set_current_chat(chat_id)` before invoking the agent.
+In M3, `handler.py` stays at the router but the agent (and `set_current_chat`) moves
+to the node. The `chat_id` travels in `ForwardRequest` (already planned), and
+`host_client/main.py` must call `set_current_chat(msg.chat_id)` before invoking the
+local `agent.run()`. This is essential for `FileSendTool` and `SchedulerTool` to work.
+
+### 3. `orchestrator/tools.py` imports `config.WORKING_DIR`
+
+`_resolve_dir()` imports `WORKING_DIR` from root `config.py`. When `orchestrator/`
+moves to the host client, this import must switch to `host_client/config.py`.
+In standalone mode, `host_client/config.py` can re-export from root `config.py` to
+keep a single `keyring.yaml`.
diff --git a/agent/task_runner.py b/agent/task_runner.py
index b3bac78..58b3fcf 100644
--- a/agent/task_runner.py
+++ b/agent/task_runner.py
@@ -30,6 +30,7 @@ class BackgroundTask:
     result: Optional[str] = None
     error: Optional[str] = None
     notify_chat_id: Optional[str] = None
+    user_id: Optional[str] = None
 
     @property
     def elapsed(self) -> float:
@@ -44,12 +45,18 @@ class TaskRunner:
     def __init__(self) -> None:
         self._tasks: Dict[str, BackgroundTask] = {}
         self._lock = asyncio.Lock()
+        self._notification_handler: Optional[Callable] = None
+
+    def set_notification_handler(self, handler: Optional[Callable]) -> None:
+        """Set custom notification handler for M3 mode (host client -> router)."""
+        self._notification_handler = handler
 
     async def submit(
         self,
         coro: Callable[[], Any],
         description: str,
         notify_chat_id: Optional[str] = None,
+        user_id: Optional[str] = None,
     ) -> str:
         """Submit a coroutine as a background task."""
         task_id = str(uuid.uuid4())[:8]
@@ -59,6 +66,7 @@ class TaskRunner:
             started_at=time.time(),
             status=TaskStatus.PENDING,
             notify_chat_id=notify_chat_id,
+            user_id=user_id,
         )
 
         async with self._lock:
@@ -94,7 +102,10 @@ class TaskRunner:
             logger.exception("Task %s failed: %s", task_id, exc)
 
         if task.notify_chat_id:
-            await self._send_notification(task)
+            if self._notification_handler:
+                await self._notification_handler(task)
+            else:
+                await self._send_notification(task)
 
     async def _send_notification(self, task: BackgroundTask) -> None:
         """Send Feishu notification about task completion."""
diff --git a/bot/commands.py b/bot/commands.py
index 55fcb00..d05d739 100644
--- a/bot/commands.py
+++ b/bot/commands.py
@@ -67,6 +67,8 @@ async def handle_command(user_id: str, text: str) -> Optional[str]:
         return await _cmd_shell(args)
     elif cmd == "/remind":
         return await _cmd_remind(args)
+    elif cmd in ("/nodes", "/node"):
+        return await _cmd_nodes(user_id, args)
     else:
         return None
 
@@ -278,6 +280,39 @@ async def _cmd_remind(args: str) -> str:
     return f"⏰ Reminder #{job_id} set for {value}{unit} from now"
 
 
+async def _cmd_nodes(user_id: str, args: str) -> str:
+    """List nodes or switch active node."""
+    from config import ROUTER_MODE
+    if not ROUTER_MODE:
+        return "Not in router mode. Run standalone.py for multi-host support."
+
+    from router.nodes import get_node_registry
+    registry = get_node_registry()
+
+    if args:
+        args = args.strip()
+        if registry.set_active_node(user_id, args):
+            return f"✓ Active node set to: {args}"
+        return f"Error: Node '{args}' not found"
+
+    nodes = registry.list_nodes()
+    if not nodes:
+        return "No nodes connected."
+
+    active_node_id = None
+    active_node = registry.get_active_node(user_id)
+    if active_node:
+        active_node_id = active_node.node_id
+
+    lines = ["**Connected Nodes:**\n"]
+    for n in nodes:
+        marker = "→ " if n["node_id"] == active_node_id else "  "
+        status = "🟢" if n["status"] == "online" else "🔴"
+        lines.append(f"{marker}{n['display_name']} {status}  sessions={n['sessions']}")
+    lines.append("\nUse `/node <name>` to switch active node.")
+    return "\n".join(lines)
+
+
 def _cmd_help() -> str:
     """Show help."""
     return """**Commands:**
@@ -290,5 +325,7 @@ def _cmd_help() -> str:
 /shell <cmd> - Run shell command (bypasses LLM)
 /remind <time> <msg> - Set reminder (e.g. /remind 10m check build)
 /tasks - List background tasks
+/nodes - List connected host nodes
+/node <name> - Switch active node
 /retry - Retry last message
 /help - Show this help"""
diff --git a/bot/handler.py b/bot/handler.py
index baa4b14..ae34c4c 100644
--- a/bot/handler.py
+++ b/bot/handler.py
@@ -86,7 +86,7 @@ def _handle_message(data: P2ImMessageReceiveV1) -> None:
 
 
 async def _process_message(user_id: str, chat_id: str, text: str) -> None:
-    """Process message: check allowlist, then commands, then agent."""
+    """Process message: check allowlist, then commands, then route to node or local agent."""
     try:
         set_current_chat(chat_id)
 
@@ -96,10 +96,48 @@ async def _process_message(user_id: str, chat_id: str, text: str) -> None:
             return
 
         reply = await handle_command(user_id, text)
-        if reply is None:
+        if reply is not None:
+            if reply:
+                await send_text(chat_id, "chat_id", reply)
+            return
+
+        from config import ROUTER_MODE
+        if ROUTER_MODE:
+            from router.routing_agent import route
+            from router.rpc import forward
+            from router.nodes import get_node_registry
+
+            node_id, reason = await route(user_id, chat_id, text)
+
+            if node_id is None:
+                await send_text(chat_id, "chat_id", f"No host available: {reason}")
+                return
+
+            if node_id == "meta":
+                registry = get_node_registry()
+                nodes = registry.list_nodes()
+                if nodes:
+                    lines = ["Connected Nodes:"]
+                    for n in nodes:
+                        marker = " → " if n.get("node_id") == registry.get_active_node(user_id) else "   "
+                        lines.append(f"{marker}{n['display_name']}  sessions={n['sessions']}  {n['status']}")
+                    lines.append("\nUse \"/node <name>\" to switch active node.")
+                    await send_text(chat_id, "chat_id", "\n".join(lines))
+                else:
+                    await send_text(chat_id, "chat_id", "No nodes connected.")
+                return
+
+            try:
+                reply = await forward(node_id, user_id, chat_id, text)
+                if reply:
+                    await send_text(chat_id, "chat_id", reply)
+            except Exception as e:
+                logger.exception("Failed to forward to node %s", node_id)
+                await send_text(chat_id, "chat_id", f"Error communicating with node: {e}")
+        else:
             reply = await agent.run(user_id, text)
-        if reply:
-            await send_text(chat_id, "chat_id", reply)
+            if reply:
+                await send_text(chat_id, "chat_id", reply)
     except Exception:
         logger.exception("Error processing message for user %s", user_id)
 
diff --git a/config.py b/config.py
index 3f11031..bf97777 100644
--- a/config.py
+++ b/config.py
@@ -1,6 +1,6 @@
 import yaml
 from pathlib import Path
-from typing import List
+from typing import List, Optional
 
 _CONFIG_PATH = Path(__file__).parent / "keyring.yaml"
 
@@ -20,6 +20,9 @@ OPENAI_MODEL: str = _cfg.get("OPENAI_MODEL", "glm-4.7")
 WORKING_DIR: Path = Path(_cfg.get("WORKING_DIR", Path.home())).expanduser().resolve()
 METASO_API_KEY: str = _cfg.get("METASO_API_KEY", "")
 
+ROUTER_MODE: bool = _cfg.get("ROUTER_MODE", False)
+ROUTER_SECRET: str = _cfg.get("ROUTER_SECRET", "")
+
 ALLOWED_OPEN_IDS: List[str] = _cfg.get("ALLOWED_OPEN_IDS", [])
 if ALLOWED_OPEN_IDS and not isinstance(ALLOWED_OPEN_IDS, list):
     ALLOWED_OPEN_IDS = [str(ALLOWED_OPEN_IDS)]
diff --git a/host_client/__init__.py b/host_client/__init__.py
new file mode 100644
index 0000000..4dbf934
--- /dev/null
+++ b/host_client/__init__.py
@@ -0,0 +1,6 @@
+"""Host client module - connects to router and runs local mailboy."""
+
+from host_client.config import HostConfig, get_host_config
+from host_client.main import NodeClient
+
+__all__ = ["HostConfig", "get_host_config", "NodeClient"]
diff --git a/host_client/config.py b/host_client/config.py
new file mode 100644
index 0000000..63bfeb4
--- /dev/null
+++ b/host_client/config.py
@@ -0,0 +1,97 @@
+"""Host client configuration loader.
+
+Loads host_config.yaml which contains:
+- NODE_ID, DISPLAY_NAME
+- ROUTER_URL, ROUTER_SECRET
+- LLM config (OPENAI_*)
+- WORKING_DIR, METASO_API_KEY
+- SERVES_USERS list
+"""
+
+from __future__ import annotations
+
+import os
+from pathlib import Path
+from typing import List, Optional
+
+import yaml
+
+
+class HostConfig:
+    """Configuration for a host client node."""
+
+    def __init__(self, config_path: Optional[Path] = None):
+        config_path = config_path or Path(__file__).parent.parent / "host_config.yaml"
+        self._load(config_path)
+
+    def _load(self, config_path: Path) -> None:
+        if not config_path.exists():
+            raise FileNotFoundError(f"Config file not found: {config_path}")
+
+        with open(config_path, "r", encoding="utf-8") as f:
+            data = yaml.safe_load(f) or {}
+
+        self.node_id: str = data.get("NODE_ID", "unknown-node")
+        self.display_name: str = data.get("DISPLAY_NAME", self.node_id)
+        self.router_url: str = data.get("ROUTER_URL", "ws://127.0.0.1:8000/ws/node")
+        self.router_secret: str = data.get("ROUTER_SECRET", "")
+
+        self.openai_base_url: str = data.get(
+            "OPENAI_BASE_URL", "https://open.bigmodel.cn/api/paas/v4/"
+        )
+        self.openai_api_key: str = data.get("OPENAI_API_KEY", "")
+        self.openai_model: str = data.get("OPENAI_MODEL", "glm-4.7")
+
+        self.working_dir: str = data.get("WORKING_DIR", str(Path.home() / "projects"))
+        self.metaso_api_key: Optional[str] = data.get("METASO_API_KEY")
+
+        serves_users = data.get("SERVES_USERS", [])
+        self.serves_users: List[str] = serves_users if isinstance(serves_users, list) else []
+
+        self.capabilities: List[str] = data.get(
+            "CAPABILITIES",
+            ["claude_code", "shell", "file_ops", "web", "scheduler"],
+        )
+
+    @classmethod
+    def from_keyring(cls, keyring_path: Optional[Path] = None) -> "HostConfig":
+        """Create config from keyring.yaml (for standalone mode)."""
+        keyring_path = keyring_path or Path(__file__).parent.parent / "keyring.yaml"
+        if not keyring_path.exists():
+            raise FileNotFoundError(f"keyring.yaml not found: {keyring_path}")
+
+        with open(keyring_path, "r", encoding="utf-8") as f:
+            data = yaml.safe_load(f) or {}
+
+        config = cls.__new__(cls)
+        config.node_id = data.get("NODE_ID", "local-node")
+        config.display_name = data.get("DISPLAY_NAME", "Local Machine")
+        config.router_url = data.get("ROUTER_URL", "ws://127.0.0.1:8000/ws/node")
+        config.router_secret = data.get("ROUTER_SECRET", "")
+
+        config.openai_base_url = data.get(
+            "OPENAI_BASE_URL", "https://open.bigmodel.cn/api/paas/v4/"
+        )
+        config.openai_api_key = data.get("OPENAI_API_KEY", "")
+        config.openai_model = data.get("OPENAI_MODEL", "glm-4.7")
+
+        config.working_dir = data.get("WORKING_DIR", str(Path.home() / "projects"))
+        config.metaso_api_key = data.get("METASO_API_KEY")
+
+        serves_users = data.get("ALLOWED_OPEN_IDS", [])
+        config.serves_users = serves_users if isinstance(serves_users, list) else []
+
+        config.capabilities = ["claude_code", "shell", "file_ops", "web", "scheduler"]
+
+        return config
+
+
+host_config: Optional[HostConfig] = None
+
+
+def get_host_config() -> HostConfig:
+    """Get the global host config instance."""
+    global host_config
+    if host_config is None:
+        host_config = HostConfig()
+    return host_config
diff --git a/host_client/main.py b/host_client/main.py
new file mode 100644
index 0000000..3f4548f
--- /dev/null
+++ b/host_client/main.py
@@ -0,0 +1,280 @@
+"""Host client main module.
+
+Connects to the router via WebSocket, receives forwarded messages,
+runs the local mailboy LLM, and sends responses back.
+"""
+
+from __future__ import annotations
+
+import asyncio
+import logging
+import secrets
+import time
+from typing import Optional
+
+import websockets
+from websockets.client import WebSocketClientProtocol
+
+from agent.manager import manager
+from agent.scheduler import scheduler
+from agent.task_runner import task_runner
+from host_client.config import HostConfig, get_host_config
+from orchestrator.agent import run as run_mailboy
+from orchestrator.tools import set_current_user, set_current_chat
+from shared import (
+    RegisterMessage,
+    ForwardRequest,
+    ForwardResponse,
+    TaskComplete,
+    Heartbeat,
+    NodeStatus,
+    encode,
+    decode,
+)
+
+logger = logging.getLogger(__name__)
+
+
+class NodeClient:
+    """WebSocket client that connects to the router and handles messages."""
+
+    def __init__(self, config: HostConfig):
+        self.config = config
+        self.ws: Optional[WebSocketClientProtocol] = None
+        self._running = False
+        self._last_heartbeat = time.time()
+        self._reconnect_delay = 1.0
+
+    async def connect(self) -> bool:
+        """Connect to the router WebSocket."""
+        headers = {}
+        if self.config.router_secret:
+            headers["Authorization"] = f"Bearer {self.config.router_secret}"
+
+        try:
+            self.ws = await websockets.connect(
+                self.config.router_url,
+                extra_headers=headers,
+                ping_interval=30,
+                ping_timeout=10,
+            )
+            logger.info("Connected to router: %s", self.config.router_url)
+            self._reconnect_delay = 1.0
+            return True
+        except Exception as e:
+            logger.error("Failed to connect to router: %s", e)
+            return False
+
+    async def register(self) -> bool:
+        """Send registration message to the router."""
+        if not self.ws:
+            return False
+
+        msg = RegisterMessage(
+            node_id=self.config.node_id,
+            display_name=self.config.display_name,
+            serves_users=self.config.serves_users,
+            working_dir=self.config.working_dir,
+            capabilities=self.config.capabilities,
+        )
+
+        try:
+            await self.ws.send(encode(msg))
+            logger.info("Sent registration for node: %s", self.config.node_id)
+            return True
+        except Exception as e:
+            logger.error("Failed to send registration: %s", e)
+            return False
+
+    async def handle_forward(self, request: ForwardRequest) -> None:
+        """Handle a forwarded message from the router."""
+        logger.info("Received forward request %s from user %s", request.id, request.user_id)
+
+        set_current_user(request.user_id)
+        set_current_chat(request.chat_id)
+
+        try:
+            reply = await run_mailboy(request.user_id, request.text)
+
+            response = ForwardResponse(
+                id=request.id,
+                reply=reply,
+                error="",
+            )
+        except Exception as e:
+            logger.exception("Error processing forward request %s", request.id)
+            response = ForwardResponse(
+                id=request.id,
+                reply="",
+                error=str(e),
+            )
+
+        if self.ws:
+            try:
+                await self.ws.send(encode(response))
+            except Exception as e:
+                logger.error("Failed to send response: %s", e)
+
+    async def send_heartbeat(self) -> None:
+        """Send a ping heartbeat to the router."""
+        if self.ws:
+            try:
+                await self.ws.send(encode(Heartbeat(type="ping")))
+                self._last_heartbeat = time.time()
+            except Exception as e:
+                logger.error("Failed to send heartbeat: %s", e)
+
+    async def send_status(self) -> None:
+        """Send node status update to the router."""
+        if not self.ws:
+            return
+
+        sessions = manager.list_sessions()
+        active_sessions = [
+            {"conv_id": s["conv_id"], "working_dir": s["working_dir"]}
+            for s in sessions
+        ]
+
+        status = NodeStatus(
+            node_id=self.config.node_id,
+            sessions=len(sessions),
+            active_sessions=active_sessions,
+        )
+
+        try:
+            await self.ws.send(encode(status))
+        except Exception as e:
+            logger.error("Failed to send status: %s", e)
+
+    async def handle_message(self, data: str) -> None:
+        """Handle an incoming message from the router."""
+        try:
+            msg = decode(data)
+        except Exception as e:
+            logger.error("Failed to decode message: %s", e)
+            return
+
+        if isinstance(msg, ForwardRequest):
+            await self.handle_forward(msg)
+        elif isinstance(msg, Heartbeat):
+            if msg.type == "ping":
+                if self.ws:
+                    try:
+                        await self.ws.send(encode(Heartbeat(type="pong")))
+                    except Exception as e:
+                        logger.error("Failed to send pong: %s", e)
+            elif msg.type == "pong":
+                self._last_heartbeat = time.time()
+        else:
+            logger.debug("Received message type: %s", msg.type)
+
+    async def receive_loop(self) -> None:
+        """Main receive loop for incoming messages."""
+        if not self.ws:
+            return
+
+        try:
+            async for data in self.ws:
+                await self.handle_message(data)
+        except websockets.ConnectionClosed as e:
+            logger.warning("Connection closed: %s", e)
+        except Exception as e:
+            logger.exception("Error in receive loop: %s", e)
+
+    async def heartbeat_loop(self) -> None:
+        """Periodic heartbeat loop."""
+        while self._running:
+            await asyncio.sleep(30)
+            if self.ws and self.ws.open:
+                await self.send_heartbeat()
+
+    async def status_loop(self) -> None:
+        """Periodic status update loop."""
+        while self._running:
+            await asyncio.sleep(60)
+            if self.ws and self.ws.open:
+                await self.send_status()
+
+    async def run(self) -> None:
+        """Main run loop with reconnection."""
+        self._running = True
+
+        await manager.start()
+        await scheduler.start()
+
+        task_runner.set_notification_handler(self._send_task_complete)
+
+        while self._running:
+            if await self.connect():
+                if await self.register():
+                    try:
+                        await asyncio.gather(
+                            self.receive_loop(),
+                            self.heartbeat_loop(),
+                            self.status_loop(),
+                        )
+                    except Exception:
+                        pass
+
+            if self._running:
+                logger.info("Reconnecting in %.1f seconds...", self._reconnect_delay)
+                await asyncio.sleep(self._reconnect_delay)
+                self._reconnect_delay = min(self._reconnect_delay * 2, 60)
+
+    async def _send_task_complete(self, task) -> None:
+        """Send TaskComplete notification to router."""
+        if not self.ws:
+            return
+
+        from shared import TaskComplete, encode
+
+        msg = TaskComplete(
+            task_id=task.task_id,
+            user_id=task.user_id or "",
+            chat_id=task.notify_chat_id or "",
+            result=task.result or task.error or "",
+        )
+
+        try:
+            await self.ws.send(encode(msg))
+            logger.info("Sent TaskComplete for task %s", task.task_id)
+        except Exception as e:
+            logger.error("Failed to send TaskComplete: %s", e)
+
+    async def stop(self) -> None:
+        """Stop the client."""
+        self._running = False
+        if self.ws:
+            await self.ws.close()
+        await manager.stop()
+        await scheduler.stop()
+        logger.info("Node client stopped")
+
+    @classmethod
+    def from_keyring(cls, router_url: Optional[str] = None, secret: Optional[str] = None) -> "NodeClient":
+        """Create a client from keyring.yaml (for standalone mode)."""
+        config = HostConfig.from_keyring()
+        if router_url:
+            config.router_url = router_url
+        if secret:
+            config.router_secret = secret
+        return cls(config)
+
+
+async def main() -> None:
+    """Entry point for standalone host client."""
+    logging.basicConfig(
+        level=logging.INFO,
+        format="%(asctime)s [%(levelname)s] %(name)s: %(message)s",
+    )
+
+    client = NodeClient(get_host_config())
+
+    try:
+        await client.run()
+    except KeyboardInterrupt:
+        await client.stop()
+
+
+if __name__ == "__main__":
+    asyncio.run(main())
diff --git a/router/__init__.py b/router/__init__.py
new file mode 100644
index 0000000..153bb28
--- /dev/null
+++ b/router/__init__.py
@@ -0,0 +1,15 @@
+"""Router module - public-facing component of PhoneWork."""
+
+from router.nodes import NodeRegistry, NodeConnection, get_node_registry
+from router.main import create_app
+from router.rpc import forward
+from router.routing_agent import route
+
+__all__ = [
+    "NodeRegistry",
+    "NodeConnection",
+    "get_node_registry",
+    "create_app",
+    "forward",
+    "route",
+]
diff --git a/router/main.py b/router/main.py
new file mode 100644
index 0000000..30924cf
--- /dev/null
+++ b/router/main.py
@@ -0,0 +1,75 @@
+"""Router main module - FastAPI app factory.
+
+Creates the FastAPI application with:
+- Feishu WebSocket client
+- Node WebSocket endpoint
+- Health check endpoints
+"""
+
+from __future__ import annotations
+
+import logging
+from typing import Optional
+
+from fastapi import FastAPI, WebSocket
+from fastapi.middleware.cors import CORSMiddleware
+
+from bot.handler import start_websocket_client
+from router.nodes import NodeRegistry, get_node_registry
+from router.ws import ws_node_endpoint
+
+logger = logging.getLogger(__name__)
+
+
+def create_app(router_secret: Optional[str] = None) -> FastAPI:
+    """Create the FastAPI application.
+
+    Args:
+        router_secret: Secret for authenticating host client connections
+    """
+    app = FastAPI(title="PhoneWork Router", version="3.0.0")
+
+    app.add_middleware(
+        CORSMiddleware,
+        allow_origins=["*"],
+        allow_credentials=True,
+        allow_methods=["*"],
+        allow_headers=["*"],
+    )
+
+    registry = get_node_registry()
+    if router_secret:
+        registry._secret = router_secret
+
+    @app.get("/health")
+    async def health():
+        nodes = registry.list_nodes()
+        online_nodes = [n for n in nodes if n["status"] == "online"]
+        return {
+            "status": "ok",
+            "nodes": nodes,
+            "online_nodes": len(online_nodes),
+            "total_nodes": len(nodes),
+            "pending_requests": 0,
+        }
+
+    @app.get("/nodes")
+    async def list_nodes():
+        return registry.list_nodes()
+
+    @app.websocket("/ws/node")
+    async def ws_node(websocket: WebSocket):
+        await ws_node_endpoint(websocket)
+
+    @app.on_event("startup")
+    async def startup():
+        import asyncio
+        loop = asyncio.get_event_loop()
+        start_websocket_client(loop)
+        logger.info("Router started")
+
+    @app.on_event("shutdown")
+    async def shutdown():
+        logger.info("Router shut down")
+
+    return app
diff --git a/router/nodes.py b/router/nodes.py
new file mode 100644
index 0000000..aba26d2
--- /dev/null
+++ b/router/nodes.py
@@ -0,0 +1,209 @@
+"""Node registry for managing connected host clients.
+
+Maintains:
+- Connected nodes with their WebSocket connections
+- User-to-node mapping (which users each node serves)
+- Active node preference per user
+"""
+
+from __future__ import annotations
+
+import asyncio
+import logging
+import time
+from dataclasses import dataclass, field
+from typing import Any, Dict, List, Optional, Set
+
+from shared import RegisterMessage, NodeStatus
+
+logger = logging.getLogger(__name__)
+
+
+@dataclass
+class NodeConnection:
+    """Represents a connected host client."""
+    node_id: str
+    ws: Any
+    display_name: str = ""
+    serves_users: Set[str] = field(default_factory=set)
+    working_dir: str = ""
+    capabilities: List[str] = field(default_factory=list)
+    connected_at: float = field(default_factory=time.time)
+    last_heartbeat: float = field(default_factory=time.time)
+    sessions: int = 0
+    active_sessions: List[Dict[str, Any]] = field(default_factory=list)
+
+    @property
+    def is_online(self) -> bool:
+        """Check if node is still considered online (heartbeat within 60s)."""
+        return time.time() - self.last_heartbeat < 60
+
+    def to_dict(self) -> Dict[str, Any]:
+        """Serialize for API responses."""
+        return {
+            "node_id": self.node_id,
+            "display_name": self.display_name,
+            "status": "online" if self.is_online else "offline",
+            "users": len(self.serves_users),
+            "sessions": self.sessions,
+            "capabilities": self.capabilities,
+            "connected_at": self.connected_at,
+            "last_heartbeat": self.last_heartbeat,
+        }
+
+
+class NodeRegistry:
+    """Registry of connected host clients."""
+
+    def __init__(self, router_secret: str = ""):
+        self._nodes: Dict[str, NodeConnection] = {}
+        self._user_nodes: Dict[str, Set[str]] = {}
+        self._active_node: Dict[str, str] = {}
+        self._secret = router_secret
+        self._lock = asyncio.Lock()
+
+    def validate_secret(self, secret: str) -> bool:
+        """Validate router secret."""
+        if not self._secret:
+            return True
+        return secret == self._secret
+
+    async def register(self, ws: Any, msg: RegisterMessage) -> NodeConnection:
+        """Register a new node connection."""
+        async with self._lock:
+            is_reconnect = msg.node_id in self._nodes
+
+            node = NodeConnection(
+                node_id=msg.node_id,
+                ws=ws,
+                display_name=msg.display_name or msg.node_id,
+                serves_users=set(msg.serves_users),
+                working_dir=msg.working_dir,
+                capabilities=msg.capabilities,
+            )
+            self._nodes[msg.node_id] = node
+
+            for user_id in msg.serves_users:
+                if user_id not in self._user_nodes:
+                    self._user_nodes[user_id] = set()
+                self._user_nodes[user_id].add(msg.node_id)
+
+            logger.info(
+                "Node registered: %s (users: %s, capabilities: %s)",
+                msg.node_id,
+                msg.serves_users,
+                msg.capabilities,
+            )
+
+            if is_reconnect:
+                for user_id in msg.serves_users:
+                    asyncio.create_task(self._notify_reconnect(user_id, node.display_name))
+
+            return node
+
+    async def _notify_reconnect(self, user_id: str, node_name: str) -> None:
+        """Notify user about node reconnect."""
+        try:
+            from bot.feishu import send_text
+            await send_text(user_id, "open_id", f"✅ Node \"{node_name}\" reconnected.")
+        except Exception as e:
+            logger.error("Failed to send reconnect notification: %s", e)
+
+    async def unregister(self, node_id: str) -> None:
+        """Unregister a node connection."""
+        async with self._lock:
+            node = self._nodes.pop(node_id, None)
+            if node:
+                affected_users = list(node.serves_users)
+
+                for user_id in node.serves_users:
+                    if user_id in self._user_nodes:
+                        self._user_nodes[user_id].discard(node_id)
+                        if not self._user_nodes[user_id]:
+                            del self._user_nodes[user_id]
+
+                for user_id in list(self._active_node.keys()):
+                    if self._active_node[user_id] == node_id:
+                        del self._active_node[user_id]
+
+                logger.info("Node unregistered: %s", node_id)
+
+                for user_id in affected_users:
+                    asyncio.create_task(self._notify_disconnect(user_id, node.display_name))
+
+    async def _notify_disconnect(self, user_id: str, node_name: str) -> None:
+        """Notify user about node disconnect."""
+        try:
+            from bot.feishu import send_text
+            await send_text(user_id, "open_id", f"⚠️ Node \"{node_name}\" disconnected.")
+        except Exception as e:
+            logger.error("Failed to send disconnect notification: %s", e)
+
+    async def update_status(self, msg: NodeStatus) -> None:
+        """Update node status from heartbeat."""
+        async with self._lock:
+            node = self._nodes.get(msg.node_id)
+            if node:
+                node.sessions = msg.sessions
+                node.active_sessions = msg.active_sessions
+                node.last_heartbeat = time.time()
+
+    async def update_heartbeat(self, node_id: str) -> None:
+        """Update node heartbeat timestamp."""
+        async with self._lock:
+            node = self._nodes.get(node_id)
+            if node:
+                node.last_heartbeat = time.time()
+
+    def get_node(self, node_id: str) -> Optional[NodeConnection]:
+        """Get a node by ID."""
+        return self._nodes.get(node_id)
+
+    def get_nodes_for_user(self, user_id: str) -> List[NodeConnection]:
+        """Get all nodes that serve a user."""
+        node_ids = self._user_nodes.get(user_id, set())
+        return [self._nodes[nid] for nid in node_ids if nid in self._nodes]
+
+    def get_active_node(self, user_id: str) -> Optional[NodeConnection]:
+        """Get the active node for a user."""
+        node_id = self._active_node.get(user_id)
+        if node_id:
+            return self._nodes.get(node_id)
+
+        nodes = self.get_nodes_for_user(user_id)
+        if nodes:
+            online = [n for n in nodes if n.is_online]
+            if online:
+                return online[0]
+
+        return None
+
+    def set_active_node(self, user_id: str, node_id: str) -> bool:
+        """Set the active node for a user."""
+        if node_id not in self._nodes:
+            return False
+        self._active_node[user_id] = node_id
+        logger.info("Active node for user %s set to %s", user_id, node_id)
+        return True
+
+    def list_nodes(self) -> List[Dict[str, Any]]:
+        """List all nodes with their status."""
+        return [node.to_dict() for node in self._nodes.values()]
+
+    def get_affected_users(self, node_id: str) -> List[str]:
+        """Get users affected by a node disconnect."""
+        node = self._nodes.get(node_id)
+        if node:
+            return list(node.serves_users)
+        return []
+
+
+node_registry: Optional[NodeRegistry] = None
+
+
+def get_node_registry() -> NodeRegistry:
+    """Get the global node registry instance."""
+    global node_registry
+    if node_registry is None:
+        node_registry = NodeRegistry()
+    return node_registry
diff --git a/router/routing_agent.py b/router/routing_agent.py
new file mode 100644
index 0000000..d812569
--- /dev/null
+++ b/router/routing_agent.py
@@ -0,0 +1,128 @@
+"""Routing LLM for deciding which node to forward messages to.
+
+This is a lightweight, one-shot LLM call that decides routing.
+No history, no multi-step loop. Single call with one tool.
+"""
+
+from __future__ import annotations
+
+import json
+import logging
+from typing import List, Optional
+
+from langchain_core.messages import HumanMessage, SystemMessage
+from langchain_openai import ChatOpenAI
+
+from config import OPENAI_API_KEY, OPENAI_BASE_URL, OPENAI_MODEL
+from router.nodes import NodeConnection, get_node_registry
+
+logger = logging.getLogger(__name__)
+
+ROUTING_SYSTEM_PROMPT = """You are a routing assistant. A user has sent a message. \
+Choose which node to forward it to.
+
+Connected nodes for this user:
+{nodes_info}
+
+Rules:
+- If the message references an active session on a node, route to that node.
+- If the user names a machine explicitly ("on work-server", "@home-pc"), route there.
+- If only one node is connected, route there without asking.
+- If ambiguous with multiple idle nodes, ask the user to clarify.
+- For meta commands (/nodes, /help, /status), respond with "meta" as the node_id.
+
+Respond with a JSON object:
+{{"node_id": "<node_id>", "reason": "<brief reason>"}}
+"""
+
+
+def _format_nodes_info(nodes: List[NodeConnection], active_node_id: Optional[str] = None) -> str:
+    """Format node information for the routing prompt."""
+    lines = []
+    for node in nodes:
+        marker = " [ACTIVE]" if node.node_id == active_node_id else ""
+        sessions = ", ".join(
+            s.get("working_dir", "unknown") for s in node.active_sessions[:3]
+        ) or "none"
+        lines.append(
+            f"- {node.display_name or node.node_id}{marker}: "
+            f"sessions=[{sessions}], capabilities={node.capabilities}"
+        )
+    return "\n".join(lines)
+
+
+async def route(user_id: str, chat_id: str, text: str) -> tuple[Optional[str], str]:
+    """Determine which node to route a message to.
+
+    Args:
+        user_id: User's Feishu open_id
+        chat_id: Chat ID for context
+        text: User's message text
+
+    Returns:
+        Tuple of (node_id, reason). node_id is None if no suitable node found.
+    """
+    registry = get_node_registry()
+    nodes = registry.get_nodes_for_user(user_id)
+
+    if not nodes:
+        return None, "No nodes available for this user"
+
+    online_nodes = [n for n in nodes if n.is_online]
+    if not online_nodes:
+        return None, "All nodes for this user are offline"
+
+    if len(online_nodes) == 1:
+        return online_nodes[0].node_id, "Only one node available"
+
+    if text.strip().startswith("/"):
+        return "meta", "Meta command"
+
+    active_node = registry.get_active_node(user_id)
+    active_node_id = active_node.node_id if active_node else None
+
+    nodes_info = _format_nodes_info(online_nodes, active_node_id)
+
+    try:
+        llm = ChatOpenAI(
+            model=OPENAI_MODEL,
+            openai_api_key=OPENAI_API_KEY,
+            openai_api_base=OPENAI_BASE_URL,
+            temperature=0,
+        )
+
+        prompt = ROUTING_SYSTEM_PROMPT.format(nodes_info=nodes_info)
+        messages = [
+            SystemMessage(content=prompt),
+            HumanMessage(content=text),
+        ]
+
+        response = await llm.ainvoke(messages)
+        content = response.content.strip()
+
+        if content.startswith("```"):
+            content = content.split("\n", 1)[1]
+            content = content.rsplit("```", 1)[0]
+
+        result = json.loads(content)
+        node_id = result.get("node_id")
+        reason = result.get("reason", "")
+
+        if node_id == "meta":
+            return "meta", reason
+
+        for node in online_nodes:
+            if node.node_id == node_id or node.display_name == node_id:
+                return node.node_id, reason
+
+        if active_node:
+            return active_node.node_id, f"Defaulting to active node (LLM suggested unavailable: {node_id})"
+
+        return online_nodes[0].node_id, f"Defaulting to first available node (LLM suggested: {node_id})"
+
+    except Exception as e:
+        logger.warning("Routing LLM failed: %s, falling back to active node", e)
+
+        if active_node:
+            return active_node.node_id, "Fallback to active node"
+        return online_nodes[0].node_id, "Fallback to first available node"
diff --git a/router/rpc.py b/router/rpc.py
new file mode 100644
index 0000000..b8e2473
--- /dev/null
+++ b/router/rpc.py
@@ -0,0 +1,109 @@
+"""RPC module for forwarding requests to host clients.
+
+Handles:
+- Request correlation with asyncio.Future
+- Timeout management
+- Response routing
+"""
+
+from __future__ import annotations
+
+import asyncio
+import logging
+import uuid
+from typing import Any, Dict, Optional
+
+from shared import ForwardRequest, ForwardResponse, TaskComplete, encode
+from router.nodes import get_node_registry
+
+logger = logging.getLogger(__name__)
+
+_pending_requests: Dict[str, asyncio.Future] = {}
+_default_timeout = 600.0
+
+
+async def forward(
+    node_id: str,
+    user_id: str,
+    chat_id: str,
+    text: str,
+    timeout: float = _default_timeout,
+) -> str:
+    """Forward a message to a host client and wait for response.
+
+    Args:
+        node_id: Target node ID
+        user_id: User's Feishu open_id
+        chat_id: Chat ID for context
+        text: Message text to forward
+        timeout: Timeout in seconds (default 600s for long CC tasks)
+
+    Returns:
+        Reply text from the host client
+
+    Raises:
+        asyncio.TimeoutError: If no response within timeout
+        RuntimeError: If node is not connected
+    """
+    registry = get_node_registry()
+    node = registry.get_node(node_id)
+
+    if not node or not node.ws:
+        raise RuntimeError(f"Node not connected: {node_id}")
+
+    request_id = str(uuid.uuid4())
+    future: asyncio.Future = asyncio.get_event_loop().create_future()
+    _pending_requests[request_id] = future
+
+    request = ForwardRequest(
+        id=request_id,
+        user_id=user_id,
+        chat_id=chat_id,
+        text=text,
+    )
+
+    try:
+        await node.ws.send_text(encode(request))
+        logger.debug("Forwarded request %s to node %s", request_id, node_id)
+
+        result = await asyncio.wait_for(future, timeout=timeout)
+        return result
+
+    except asyncio.TimeoutError:
+        logger.warning("Request %s timed out after %ss", request_id, timeout)
+        raise
+
+    except Exception as e:
+        logger.error("Failed to forward request %s: %s", request_id, e)
+        raise
+
+    finally:
+        _pending_requests.pop(request_id, None)
+
+
+async def resolve_response(response: ForwardResponse) -> None:
+    """Resolve a pending request with a response."""
+    future = _pending_requests.get(response.id)
+    if future and not future.done():
+        if response.error:
+            future.set_exception(RuntimeError(response.error))
+        else:
+            future.set_result(response.reply)
+        logger.debug("Resolved request %s", response.id)
+
+
+async def handle_task_complete(msg: TaskComplete) -> None:
+    """Handle a task completion notification from a host client."""
+    logger.info("Task %s completed for user %s", msg.task_id, msg.user_id)
+
+    from bot.feishu import send_text
+
+    try:
+        await send_text(msg.chat_id, "chat_id", msg.result)
+    except Exception as e:
+        logger.error("Failed to send task completion notification: %s", e)
+
+
+def get_pending_count() -> int:
+    """Get the number of pending requests."""
+    return len(_pending_requests)
diff --git a/router/ws.py b/router/ws.py
new file mode 100644
index 0000000..52bb7ab
--- /dev/null
+++ b/router/ws.py
@@ -0,0 +1,102 @@
+"""WebSocket endpoint for host client connections.
+
+Handles:
+- Connection authentication
+- Node registration
+- Message forwarding
+- Heartbeat
+"""
+
+from __future__ import annotations
+
+import asyncio
+import logging
+from typing import Optional
+
+from fastapi import WebSocket, WebSocketDisconnect, WebSocketException
+
+from router.nodes import get_node_registry
+from router.rpc import handle_task_complete
+from shared import (
+    RegisterMessage,
+    ForwardRequest,
+    ForwardResponse,
+    TaskComplete,
+    Heartbeat,
+    NodeStatus,
+    decode,
+    encode,
+)
+
+logger = logging.getLogger(__name__)
+
+
+async def ws_node_endpoint(websocket: WebSocket) -> None:
+    """WebSocket endpoint for host client connections."""
+    await websocket.accept()
+
+    registry = get_node_registry()
+
+    secret = websocket.headers.get("authorization", "")
+    if secret.startswith("Bearer "):
+        secret = secret[7:]
+
+    if not registry.validate_secret(secret):
+        logger.warning("Invalid router secret, rejecting connection")
+        await websocket.close(code=4001, reason="Invalid secret")
+        return
+
+    node_id: Optional[str] = None
+    heartbeat_task: Optional[asyncio.Task] = None
+
+    async def send_heartbeat():
+        """Send periodic pings to the host client."""
+        try:
+            while True:
+                await asyncio.sleep(30)
+                try:
+                    await websocket.send_text(encode(Heartbeat(type="ping")))
+                except Exception:
+                    break
+        except asyncio.CancelledError:
+            pass
+
+    try:
+        async for data in websocket.iter_text():
+            try:
+                msg = decode(data)
+            except Exception as e:
+                logger.error("Failed to decode message: %s", e)
+                continue
+
+            if isinstance(msg, RegisterMessage):
+                node_id = msg.node_id
+                await registry.register(websocket, msg)
+                heartbeat_task = asyncio.create_task(send_heartbeat())
+
+            elif isinstance(msg, ForwardResponse):
+                from router.rpc import resolve_response
+                await resolve_response(msg)
+
+            elif isinstance(msg, TaskComplete):
+                await handle_task_complete(msg)
+
+            elif isinstance(msg, Heartbeat):
+                if msg.type == "pong" and node_id:
+                    await registry.update_heartbeat(node_id)
+
+            elif isinstance(msg, NodeStatus):
+                await registry.update_status(msg)
+
+            else:
+                logger.debug("Received unhandled message type: %s", type(msg).__name__)
+
+    except WebSocketDisconnect:
+        logger.info("WebSocket disconnected")
+    except Exception as e:
+        logger.exception("WebSocket error: %s", e)
+    finally:
+        if heartbeat_task:
+            heartbeat_task.cancel()
+        if node_id:
+            await registry.unregister(node_id)
diff --git a/shared/__init__.py b/shared/__init__.py
new file mode 100644
index 0000000..a4f7a30
--- /dev/null
+++ b/shared/__init__.py
@@ -0,0 +1,23 @@
+"""Shared module for Router <-> Host Client communication."""
+
+from shared.protocol import (
+    RegisterMessage,
+    ForwardRequest,
+    ForwardResponse,
+    TaskComplete,
+    Heartbeat,
+    NodeStatus,
+    encode,
+    decode,
+)
+
+__all__ = [
+    "RegisterMessage",
+    "ForwardRequest",
+    "ForwardResponse",
+    "TaskComplete",
+    "Heartbeat",
+    "NodeStatus",
+    "encode",
+    "decode",
+]
diff --git a/shared/protocol.py b/shared/protocol.py
new file mode 100644
index 0000000..8de2225
--- /dev/null
+++ b/shared/protocol.py
@@ -0,0 +1,94 @@
+"""Shared protocol module for Router <-> Host Client communication.
+
+All message types are dataclasses that serialize to/from JSON.
+Both router and host client import from this module.
+"""
+
+from __future__ import annotations
+
+import json
+from dataclasses import asdict, dataclass, field
+from typing import Any, Dict, List, Optional
+
+
+@dataclass
+class RegisterMessage:
+    """Host client -> Router: Register this node."""
+    type: str = "register"
+    node_id: str = ""
+    serves_users: List[str] = field(default_factory=list)
+    working_dir: str = ""
+    capabilities: List[str] = field(default_factory=list)
+    display_name: str = ""
+
+
+@dataclass
+class ForwardRequest:
+    """Router -> Host client: Forward a user message."""
+    type: str = "forward"
+    id: str = ""
+    user_id: str = ""
+    chat_id: str = ""
+    text: str = ""
+
+
+@dataclass
+class ForwardResponse:
+    """Host client -> Router: Reply to a forwarded message."""
+    type: str = "forward_response"
+    id: str = ""
+    reply: str = ""
+    error: str = ""
+
+
+@dataclass
+class TaskComplete:
+    """Host client -> Router: Background task finished."""
+    type: str = "task_complete"
+    task_id: str = ""
+    user_id: str = ""
+    chat_id: str = ""
+    result: str = ""
+
+
+@dataclass
+class Heartbeat:
+    """Bidirectional ping/pong."""
+    type: str = "ping"
+
+
+@dataclass
+class NodeStatus:
+    """Host client -> Router: Periodic status update."""
+    type: str = "node_status"
+    node_id: str = ""
+    sessions: int = 0
+    active_sessions: List[Dict[str, Any]] = field(default_factory=list)
+
+
+MESSAGE_TYPES = {
+    "register": RegisterMessage,
+    "forward": ForwardRequest,
+    "forward_response": ForwardResponse,
+    "task_complete": TaskComplete,
+    "ping": Heartbeat,
+    "pong": Heartbeat,
+    "node_status": NodeStatus,
+}
+
+
+def encode(msg: Any) -> str:
+    """Encode a message to JSON string."""
+    if hasattr(msg, "type"):
+        return json.dumps(asdict(msg), ensure_ascii=False)
+    raise ValueError(f"Invalid message type: {type(msg)}")
+
+
+def decode(data: str) -> Any:
+    """Decode a JSON string to a message object."""
+    obj = json.loads(data)
+    msg_type = obj.get("type")
+    if msg_type not in MESSAGE_TYPES:
+        raise ValueError(f"Unknown message type: {msg_type}")
+    cls = MESSAGE_TYPES[msg_type]
+    return cls(**{k: v for k, v in obj.items() if k in cls.__dataclass_fields__})
diff --git a/standalone.py b/standalone.py
new file mode 100644
index 0000000..86171b6
--- /dev/null
+++ b/standalone.py
@@ -0,0 +1,72 @@
+"""Run router + host client in a single process (localhost mode).
+
+Equivalent to the pre-M3 single-machine setup.
+Users run `python standalone.py` and get the exact same experience as `python main.py`,
+but the code paths use the multi-host architecture internally.
+"""
+
+from __future__ import annotations
+
+import asyncio
+import logging
+import secrets
+import sys
+
+import uvicorn
+
+logging.basicConfig(
+    level=logging.INFO,
+    format="%(asctime)s [%(levelname)s] %(name)s: %(message)s",
+)
+logger = logging.getLogger(__name__)
+
+
+async def run_standalone() -> None:
+    """Run router + host client in a single process."""
+    secret = secrets.token_hex(16)
+    router_url = "ws://127.0.0.1:8000/ws/node"
+
+    from router.main import create_app
+    from host_client.main import NodeClient
+    from host_client.config import HostConfig
+
+    config = HostConfig.from_keyring()
+    config.router_url = router_url
+    config.router_secret = secret
+
+    app = create_app(router_secret=secret)
+
+    config_obj = uvicorn.Config(
+        app,
+        host="0.0.0.0",
+        port=8000,
+        log_level="info",
+    )
+    server = uvicorn.Server(config_obj)
+
+    async def run_server():
+        await server.serve()
+
+    async def run_client():
+        await asyncio.sleep(1.5)
+        client = NodeClient(config)
+        try:
+            await client.run()
+        except Exception as e:
+            logger.exception("Host client error: %s", e)
+            server.should_exit = True
+
+    await asyncio.gather(run_server(), run_client())
+
+
+def main() -> None:
+    """Entry point."""
+    logger.info("Starting PhoneWork in standalone mode...")
+    try:
+        asyncio.run(run_standalone())
+    except KeyboardInterrupt:
+        logger.info("Shutting down...")
+
+
+if __name__ == "__main__":
+    main()