Merge branch 'worktree-host-agent-mcp-server' — Host-Agent MCP Server

Adds a Streamable HTTP MCP server (mount /mcp, port 8765) to the
device-host-agent process so Hermes Agent (or any MCP client) can
drive devices directly, coexisting with the Cloud Control Plane
worker path. Per-device session-level locking with 20s TTL,
independent bearer-token auth, and bidirectional cloud ↔ MCP
coordination via a new heartbeat field.

Implementation:
- 4 new modules (mcp_token, mcp_lock, web/mcp_auth, web/mcp)
- Console mount at /mcp with bearer auth sub-app
- Cloud heartbeat payload + scheduler skip MCP-busy devices
- AssignmentExecutor fail-fast reverse check
- CLI mcp-token subcommand
- docs/MCP_INTEGRATION.md + MACOS_IPHONE_SETUP.md section

Spec: docs/superpowers/specs/2026-07-21-host-agent-mcp-server-design.md
Plan: docs/superpowers/plans/2026-07-21-host-agent-mcp-server.md

18 implementation commits ( Tasks 1-15 + final fix wave).
Spec/plan cherry-picks are detected as already-applied via patch-id.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

# Conflicts:
#	docs/superpowers/specs/2026-07-21-host-agent-mcp-server-design.md

api/mcp.py

@@ -3,7 +3,7 @@ from collections.abc import Callable
 from typing import Any
 
 from api.errors import call_with_semantic_errors
-from device.manager import DEFAULT_MANAGER, DeviceManager
+from device.manager import DeviceManager
 from tools.describe_screen import describe_screen
 from tools.find_icon import find_icon_on_screen
 from tools.find_text import find_text_on_screen
@@ -17,12 +17,11 @@ from tools.ui_tree import get_ui_tree
 
 def tool_handlers(
     *,
-    manager: DeviceManager | None = None,
+    manager: DeviceManager,
 ) -> dict[str, Callable[..., Any]]:
-    device_manager = manager or DEFAULT_MANAGER
 
     def _screenshot(device_id: str | None = None) -> dict[str, Any]:
-        image = take_screenshot(device_id, manager=device_manager)
+        image = take_screenshot(device_id, manager=manager)
         return {
             "ok": True,
             "image_base64": base64.b64encode(image).decode("ascii"),
@@ -39,65 +38,65 @@ def tool_handlers(
             x,
             y,
             device_id=device_id,
-            manager=device_manager,
+            manager=manager,
         ),
-        "swipe": lambda start_x, start_y, end_x, end_y, duration_ms=500, device_id=None: call_with_semantic_errors(
+        "swipe": lambda start_x, start_y, end_x, end_y, duration_ms=500, device_id=None: (
-            swipe,
+            call_with_semantic_errors(
-            start_x,
+                swipe,
-            start_y,
+                start_x,
-            end_x,
+                start_y,
-            end_y,
+                end_x,
-            duration_ms=duration_ms,
+                end_y,
-            device_id=device_id,
+                duration_ms=duration_ms,
-            manager=device_manager,
+                device_id=device_id,
+                manager=manager,
+            )
         ),
         "input_text": lambda text, device_id=None: call_with_semantic_errors(
             input_text,
             text,
             device_id=device_id,
-            manager=device_manager,
+            manager=manager,
         ),
         "launch_app": lambda app_id, device_id=None: call_with_semantic_errors(
             launch_app,
             app_id,
             device_id=device_id,
-            manager=device_manager,
+            manager=manager,
         ),
         "find_text": lambda query, device_id=None: call_with_semantic_errors(
             find_text_on_screen,
             query,
             device_id=device_id,
-            manager=device_manager,
+            manager=manager,
         ),
         "find_icon": lambda name, device_id=None: call_with_semantic_errors(
             find_icon_on_screen,
             name,
             device_id=device_id,
-            manager=device_manager,
+            manager=manager,
         ),
         "get_ui_tree": lambda device_id=None, include_app_info=False: (
             call_with_semantic_errors(
                 get_ui_tree,
                 device_id,
-                manager=device_manager,
+                manager=manager,
                 include_app_info=include_app_info,
             )
         ),
         "describe_screen": lambda device_id=None: call_with_semantic_errors(
-            lambda: describe_screen(device_id, manager=device_manager).to_dict()
+            lambda: describe_screen(device_id, manager=manager).to_dict()
         ),
-        "list_devices": lambda: [
+        "list_devices": lambda: [device.to_dict() for device in manager.list_devices()],
-            device.to_dict() for device in device_manager.list_devices()
-        ],
         "device_status": lambda device_id: call_with_semantic_errors(
-            lambda: {"device_id": device_id, "status": device_manager.status(device_id)}
+            lambda: {"device_id": device_id, "status": manager.status(device_id)}
         ),
     }
 
 
 def create_mcp_server(
     *,
-    manager: DeviceManager | None = None,
+    manager: DeviceManager,
     skill_catalog_store: Any | None = None,
     skill_active_subscriptions: set[str] | None = None,
     skill_local_store: Any | None = None,
@@ -107,6 +106,9 @@ def create_mcp_server(
     except ImportError as exc:
         raise RuntimeError("mcp SDK is not installed") from exc
 
+    if manager is None:
+        raise ValueError("create_mcp_server requires a non-None manager")
+
     handlers = tool_handlers(manager=manager)
     server = FastMCP("apex-agent")
 

apps/device-host-agent/host_agent/app.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import asyncio
+import logging
 from contextlib import suppress
 from dataclasses import dataclass
 
@@ -21,6 +22,8 @@ from host_agent.identity import HostIdentityStore
 from host_agent.instance_lock import InstanceLock
 from host_agent.lease import ActiveAssignmentRunner
 from host_agent.local_account import LocalAccountStore
+from host_agent.mcp_lock import McpBusyTracker
+from host_agent.mcp_token import McpTokenStore
 from host_agent.policy_cache import HostPolicyCacheStore
 from host_agent.processor import AssignmentProcessingResult, AssignmentProcessor
 from host_agent.retention import prune_task_history
@@ -28,6 +31,7 @@ from host_agent.skill_sync import HostAgentSkillSync
 from host_agent.status import AgentStatusTracker
 from host_agent.web.app import create_console_app
 from host_agent.web.auth import SessionManager
+from host_agent.web.mcp import build_mcp_server
 from storage.artifact_store import ArtifactStore
 from storage.device_config import DeviceConfigStore
 from storage.task_metadata import TaskMetadataStore
@@ -201,13 +205,28 @@ def create_application(
             db_path=resolved_config.task_progress_db_path
         )
         timeline = Timeline(ArtifactStore(root=resolved_config.task_artifact_dir))
+        mcp_token_path = resolved_config.identity_path.parent / "host_mcp_token.json"
+        mcp_token_existed = mcp_token_path.exists()
+        mcp_token_store = McpTokenStore(mcp_token_path)
+        mcp_token_store.load_or_create()
+        if not mcp_token_existed:
+            logging.getLogger(__name__).info(
+                "MCP token generated at %s", mcp_token_path
+            )
+        mcp_busy_tracker = McpBusyTracker(ttl_seconds=20.0)
         executor = AssignmentExecutor(
             create_execution_factories(
                 resolved_manager,
                 metadata_store=metadata_store,
                 timeline=timeline,
                 host_agent_config=resolved_config,
-            )
+            ),
+            mcp_busy_tracker=mcp_busy_tracker,
+        )
+        mcp_server = build_mcp_server(
+            manager=resolved_manager,
+            mcp_busy_tracker=mcp_busy_tracker,
+            status_tracker=status_tracker,
         )
         console_app = create_console_app(
             config=resolved_config,
@@ -225,6 +244,9 @@ def create_application(
             metadata_store=metadata_store,
             timeline=timeline,
             executor=executor,
+            mcp_server=mcp_server,
+            mcp_token_store=mcp_token_store,
+            mcp_busy_tracker=mcp_busy_tracker,
         )
         console_server = _EmbeddedConsoleServer(
             uvicorn.Config(
@@ -240,6 +262,7 @@ def create_application(
             client,
             resolved_config,
             status_tracker=status_tracker,
+            mcp_busy_tracker=mcp_busy_tracker,
             on_sync=lambda device_count: history_store.record_heartbeat(
                 device_count=device_count
             ),

apps/device-host-agent/host_agent/assignment.py

@@ -2,7 +2,7 @@ from __future__ import annotations
 
 from collections.abc import Callable
 from dataclasses import dataclass, field
-from typing import Any
+from typing import TYPE_CHECKING, Any
 
 from cloud.internal_api.models import AssignmentModel
 from core.models import Task
@@ -11,6 +11,9 @@ from host_agent.planner_context import bind_planner_execution_context
 from host_agent.progress import TaskProgressHolder, TaskProgressSnapshot
 from runtime.task import is_cancellation_reason
 
+if TYPE_CHECKING:
+    from host_agent.mcp_lock import McpBusyTracker
+
 
 @dataclass(frozen=True)
 class AssignmentExecutionResult:
@@ -20,9 +23,15 @@ class AssignmentExecutionResult:
 
 
 class AssignmentExecutor:
-    def __init__(self, factories: ExecutionFactories) -> None:
+    def __init__(
+        self,
+        factories: ExecutionFactories,
+        *,
+        mcp_busy_tracker: McpBusyTracker | None = None,
+    ) -> None:
         self.factories = factories
         self._progress = TaskProgressHolder()
+        self._mcp_busy_tracker = mcp_busy_tracker
 
     def latest_progress(self) -> TaskProgressSnapshot | None:
         """Latest step progress reported by the currently-running assignment."""
@@ -36,6 +45,15 @@ class AssignmentExecutor:
         stop_reason: Callable[[], str | None] | None = None,
     ) -> AssignmentExecutionResult:
         self._progress.clear()
+        if self._mcp_busy_tracker is not None and (
+            assignment.device_id in self._mcp_busy_tracker.busy_device_ids()
+        ):
+            return AssignmentExecutionResult(
+                status="failed",
+                failure_reason=(
+                    f"device {assignment.device_id} is held by an active MCP session"
+                ),
+            )
         with bind_planner_execution_context(assignment):
             if should_stop is not None and should_stop():
                 reason = stop_reason() if stop_reason is not None else None

apps/device-host-agent/host_agent/cli.py

@@ -10,6 +10,7 @@ from host_agent.app import create_application
 from host_agent.config import load_host_agent_config
 from host_agent.instance_lock import InstanceAlreadyRunningError
 from host_agent.local_account import LocalAccountStore
+from host_agent.mcp_token import McpTokenStore
 
 
 class LocalAccountSetupError(RuntimeError):
@@ -20,8 +21,16 @@ def main(argv: Sequence[str] | None = None) -> None:
     parser = argparse.ArgumentParser(description="Run the Device Host Agent")
     subparsers = parser.add_subparsers(dest="command")
     subparsers.add_parser("setup", help="Create the local operator account")
+    subparsers.add_parser(
+        "mcp-token",
+        help="Print the MCP server bearer token (generating if missing)",
+    )
     args = parser.parse_args(argv)
 
+    if args.command == "mcp-token":
+        _print_mcp_token()
+        return
+
     try:
         if args.command == "setup":
             _run_setup()
@@ -54,6 +63,12 @@ def _run_setup() -> None:
     print(f"Local account '{account.username}' created.")
 
 
+def _print_mcp_token() -> None:
+    config = load_host_agent_config()
+    store = McpTokenStore(config.identity_path.parent / "host_mcp_token.json")
+    print(store.load_or_create().token)
+
+
 def _resolve_config_with_local_account():
     config = load_host_agent_config()
     store = LocalAccountStore(config.local_account_path)

apps/device-host-agent/host_agent/client.py

@@ -168,17 +168,21 @@ class HostAgentClient:
         *,
         address: str | None = None,
         policy_revision: int = 0,
+        mcp_busy_device_ids: list[str] | None = None,
     ) -> HeartbeatResponse:
+        payload: dict[str, Any] = {
+            "host_id": self.config.host_id,
+            "address": address,
+            "devices": [device.model_dump(mode="json") for device in devices],
+            "policy_revision": policy_revision,
+            "planner_transport": self.config.ai_planner_transport,
+        }
+        if mcp_busy_device_ids:
+            payload["mcp_busy_device_ids"] = list(mcp_busy_device_ids)
         response = await self._request(
             "PUT",
             f"/internal/v1/hosts/{self.config.host_id}/heartbeat",
-            json={
+            json=payload,
-                "host_id": self.config.host_id,
-                "address": address,
-                "devices": [device.model_dump(mode="json") for device in devices],
-                "policy_revision": policy_revision,
-                "planner_transport": self.config.ai_planner_transport,
-            },
         )
         return HeartbeatResponse.model_validate(response.json())
 

apps/device-host-agent/host_agent/heartbeat.py

@@ -14,6 +14,8 @@ from host_agent.status import AgentStatusTracker
 if TYPE_CHECKING:
     from collections.abc import Awaitable, Callable
 
+    from host_agent.mcp_lock import McpBusyTracker
+
 
 def build_device_snapshot(manager: DeviceManager) -> list[DeviceSnapshotModel]:
     return [
@@ -40,6 +42,7 @@ class HeartbeatSynchronizer:
         on_sync: Callable[[int], None] | None = None,
         policy_cache: HostPolicyCacheStore | None = None,
         on_policy_sync: Callable[[int], None] | None = None,
+        mcp_busy_tracker: McpBusyTracker | None = None,
     ) -> None:
         self.manager = manager
         self.client = client
@@ -50,6 +53,7 @@ class HeartbeatSynchronizer:
         self.on_sync = on_sync
         self.policy_cache = policy_cache
         self.on_policy_sync = on_policy_sync
+        self.mcp_busy_tracker = mcp_busy_tracker
         self.policy = policy_cache.load() if policy_cache is not None else None
         self.policy_revision = self.policy.revision if self.policy is not None else 0
         if self.status_tracker is not None:
@@ -57,10 +61,16 @@ class HeartbeatSynchronizer:
 
     async def sync_once(self) -> HeartbeatResponse:
         snapshot = build_device_snapshot(self.manager)
+        mcp_busy_ids = (
+            self.mcp_busy_tracker.busy_device_ids()
+            if self.mcp_busy_tracker is not None
+            else []
+        )
         response = await self.client.heartbeat(
             snapshot,
             address=self.address,
             policy_revision=self.policy_revision,
+            mcp_busy_device_ids=mcp_busy_ids,
         )
         self.policy_revision = response.policy_revision
         if response.policy is not None:

apps/device-host-agent/host_agent/mcp_lock.py

@@ -0,0 +1,155 @@
+"""Per-device MCP session-level busy tracker.
+
+The cloud-side assignment path and the MCP-driven path both drive devices
+through the same in-process ``DeviceManager``. This tracker records which
+devices are currently held by an MCP session so that:
+
+- MCP tool calls against a device held by another session (or by a cloud
+  assignment — checked separately by the caller via ``AgentStatusTracker``)
+  can fail fast with a busy error.
+- The heartbeat payload can advertise ``mcp_busy_device_ids`` so the cloud
+  scheduler won't dispatch conflicting assignments to the same device.
+
+Leases expire ``ttl_seconds`` after the last ``renew()`` call (set on every
+tool call from the holding session). Expired leases are lazy-swept on read.
+"""
+
+from __future__ import annotations
+
+import time
+from dataclasses import dataclass
+from datetime import UTC, datetime
+from threading import Lock
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from collections.abc import Callable
+
+
+@dataclass(frozen=True)
+class McpDeviceLease:
+    device_id: str
+    session_id: str
+    acquired_at: datetime
+    last_seen_at: datetime
+
+
+class McpBusyTracker:
+    def __init__(
+        self,
+        *,
+        ttl_seconds: float = 20.0,
+        now: Callable[[], datetime] | None = None,
+    ) -> None:
+        self._ttl = float(ttl_seconds)
+        self._now = now or (lambda: datetime.now(UTC))
+        self._lock = Lock()
+        # device_id -> McpDeviceLease
+        self._leases: dict[str, McpDeviceLease] = {}
+
+    def acquire(self, device_id: str, session_id: str) -> bool:
+        with self._lock:
+            self._sweep_locked()
+            existing = self._leases.get(device_id)
+            if existing is not None and existing.session_id != session_id:
+                return False
+            now = self._now()
+            lease = McpDeviceLease(
+                device_id=device_id,
+                session_id=session_id,
+                acquired_at=(existing.acquired_at if existing is not None else now),
+                last_seen_at=now,
+            )
+            self._leases[device_id] = lease
+            return True
+
+    def renew(self, device_id: str, session_id: str) -> bool:
+        with self._lock:
+            self._sweep_locked()
+            existing = self._leases.get(device_id)
+            # Tolerate boundary: lease may have been swept, but if the caller
+            # is the legitimate previous holder, re-acquire on their behalf.
+            if existing is None:
+                now = self._now()
+                self._leases[device_id] = McpDeviceLease(
+                    device_id=device_id,
+                    session_id=session_id,
+                    acquired_at=now,
+                    last_seen_at=now,
+                )
+                return True
+            if existing.session_id != session_id:
+                return False
+            self._leases[device_id] = McpDeviceLease(
+                device_id=device_id,
+                session_id=session_id,
+                acquired_at=existing.acquired_at,
+                last_seen_at=self._now(),
+            )
+            return True
+
+    def release(self, session_id: str) -> list[str]:
+        with self._lock:
+            freed = [
+                device_id
+                for device_id, lease in self._leases.items()
+                if lease.session_id == session_id
+            ]
+            for device_id in freed:
+                del self._leases[device_id]
+            return freed
+
+    def release_device(self, device_id: str, session_id: str) -> bool:
+        with self._lock:
+            existing = self._leases.get(device_id)
+            if existing is None or existing.session_id != session_id:
+                return False
+            del self._leases[device_id]
+            return True
+
+    def busy_device_ids(self) -> list[str]:
+        with self._lock:
+            self._sweep_locked()
+            return sorted(self._leases)
+
+    def snapshot(self) -> list[McpDeviceLease]:
+        with self._lock:
+            self._sweep_locked()
+            return sorted(self._leases.values(), key=lambda lease: lease.device_id)
+
+    def wait_until_usable(
+        self,
+        device_id: str,
+        session_id: str,
+        *,
+        timeout: float,
+        poll_interval: float = 1.0,
+        cloud_busy_check: Callable[[], bool] | None = None,
+    ) -> bool:
+        """Block until ``device_id`` is acquirable by ``session_id`` or timeout.
+
+        Reserved capability. MVP callers use try-acquire (``acquire`` -> False
+        means busy). This method exists for future wiring where the cloud
+        assignment path or an explicit MCP tool may opt to wait.
+        """
+        deadline = time.monotonic() + timeout
+        while True:
+            cloud_busy = cloud_busy_check() if cloud_busy_check else False
+            if not cloud_busy:
+                if self.acquire(device_id, session_id):
+                    return True
+            if time.monotonic() >= deadline:
+                return False
+            remaining = deadline - time.monotonic()
+            time.sleep(max(0.0, min(poll_interval, remaining)))
+
+    def _sweep_locked(self) -> None:
+        """Caller holds ``self._lock``. Drops leases past their TTL."""
+        cutoff = self._now()
+        expired = [
+            device_id
+            for device_id, lease in self._leases.items()
+            if (cutoff - lease.last_seen_at).total_seconds() > self._ttl
+        ]
+        for device_id in expired:
+            del self._leases[device_id]

apps/device-host-agent/host_agent/mcp_token.py

@@ -0,0 +1,116 @@
+"""Bearer-token persistence for the host-agent MCP server.
+
+The token is generated on first start and persisted to a JSON file with
+0o600 permissions (POSIX) alongside the host identity. Rotation = delete
+the file and restart host-agent.
+"""
+
+from __future__ import annotations
+
+import json
+import os
+import secrets
+import tempfile
+from dataclasses import dataclass
+from datetime import UTC, datetime
+from pathlib import Path
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from collections.abc import Callable
+
+
+_TOKEN_BYTES = 32
+
+
+class McpTokenStoreError(RuntimeError):
+    """Raised when the MCP token file cannot be read or written."""
+
+
+@dataclass(frozen=True)
+class McpToken:
+    version: int
+    token: str
+    created_at: datetime
+
+
+class McpTokenStore:
+    def __init__(
+        self,
+        path: Path,
+        *,
+        now: Callable[[], datetime] | None = None,
+    ) -> None:
+        self._path = Path(path)
+        self._now = now or (lambda: datetime.now(UTC))
+
+    def load_or_create(self) -> McpToken:
+        if self._path.exists():
+            return self._read_existing()
+        return self._generate_and_write()
+
+    def verify(self, presented: str) -> bool:
+        try:
+            token = self.load_or_create()
+        except McpTokenStoreError:
+            return False
+        import hmac
+
+        return hmac.compare_digest(token.token, presented)
+
+    def _read_existing(self) -> McpToken:
+        try:
+            data = json.loads(self._path.read_text())
+        except (OSError, json.JSONDecodeError) as exc:
+            raise McpTokenStoreError(
+                f"cannot read MCP token file {self._path}: {exc}"
+            ) from exc
+        if not isinstance(data, dict):
+            raise McpTokenStoreError("MCP token file is not a JSON object")
+        try:
+            return McpToken(
+                version=int(data["version"]),
+                token=str(data["token"]),
+                created_at=datetime.fromisoformat(str(data["created_at"])),
+            )
+        except (KeyError, TypeError, ValueError) as exc:
+            raise McpTokenStoreError(f"MCP token file schema invalid: {exc}") from exc
+
+    def _generate_and_write(self) -> McpToken:
+        token = McpToken(
+            version=1,
+            token=secrets.token_urlsafe(_TOKEN_BYTES),
+            created_at=self._now(),
+        )
+        payload = {
+            "version": token.version,
+            "token": token.token,
+            "created_at": token.created_at.isoformat(),
+        }
+        try:
+            self._atomic_write(json.dumps(payload, indent=2))
+        except OSError as exc:
+            raise McpTokenStoreError(
+                f"cannot write MCP token file {self._path}: {exc}"
+            ) from exc
+        return token
+
+    def _atomic_write(self, content: str) -> None:
+        self._path.parent.mkdir(parents=True, exist_ok=True)
+        # Atomic on POSIX; on Windows os.replace is also atomic per docs.
+        fd, tmp_name = tempfile.mkstemp(
+            prefix=".host_mcp_token.",
+            suffix=".tmp",
+            dir=str(self._path.parent),
+        )
+        try:
+            with os.fdopen(fd, "w", encoding="utf-8") as fh:
+                fh.write(content)
+            os.chmod(tmp_name, 0o600)
+            os.replace(tmp_name, self._path)
+        except BaseException:
+            try:
+                os.unlink(tmp_name)
+            except OSError:
+                pass
+            raise

apps/device-host-agent/host_agent/web/app.py

@@ -5,7 +5,7 @@ import base64
 import json
 from collections.abc import Awaitable, Callable
 from pathlib import Path
-from typing import Any
+from typing import TYPE_CHECKING, Any
 
 import jinja2
 from fastapi import Depends, FastAPI, HTTPException, Request
@@ -24,6 +24,8 @@ from host_agent.devices import register_local_device, unregister_local_device
 from host_agent.history import ConsoleHistoryStore
 from host_agent.identity import HostIdentityStore
 from host_agent.local_account import LocalAccountStore
+from host_agent.mcp_lock import McpBusyTracker
+from host_agent.mcp_token import McpTokenStore
 from host_agent.status import AgentStatusTracker
 from host_agent.web.auth import (
     SessionManager,
@@ -31,7 +33,11 @@ from host_agent.web.auth import (
     attempt_login,
     change_password,
 )
+from host_agent.web.mcp_auth import BearerAuthMiddleware
 from storage.device_config import DeviceConfigStore
+
+if TYPE_CHECKING:
+    from mcp.server.fastmcp import FastMCP
 from storage.task_metadata import TaskMetadataStore
 from storage.timeline import Timeline
 
@@ -223,6 +229,9 @@ def create_console_app(
     metadata_store: TaskMetadataStore | None = None,
     timeline: Timeline | None = None,
     executor: AssignmentExecutor | None = None,
+    mcp_server: FastMCP | None = None,
+    mcp_token_store: McpTokenStore | None = None,
+    mcp_busy_tracker: McpBusyTracker | None = None,
 ) -> FastAPI:
     app = FastAPI(title="Host Agent Console")
     cookie_secure = config.console_bind_host not in _LOOPBACK_BIND_HOSTS
@@ -231,6 +240,18 @@ def create_console_app(
     if cancel_task is None and host_client is not None:
         cancel_task = host_client.cancel_task
     submission_available = submit_self_task is not None
+    mcp_mounted = mcp_server is not None and mcp_token_store is not None
+    if mcp_mounted:
+        from starlette.applications import Starlette
+        from starlette.middleware import Middleware
+
+        mcp_asgi = mcp_server.streamable_http_app()
+        authed = Starlette(
+            routes=[],
+            middleware=[Middleware(BearerAuthMiddleware, token_store=mcp_token_store)],
+        )
+        authed.router.mount("/", mcp_asgi)
+        app.mount("/mcp", authed)
 
     def _running_devices() -> list[dict[str, str]]:
         return [
@@ -340,6 +361,10 @@ def create_console_app(
             for d in manager.list_devices()
         ]
         texts = _dashboard_texts(snapshot=snapshot)
+        mcp_endpoint = "/mcp" if mcp_mounted else None
+        mcp_busy_devices = (
+            mcp_busy_tracker.busy_device_ids() if mcp_busy_tracker is not None else []
+        )
         return _render(
             "dashboard.html",
             title="Status",
@@ -347,6 +372,8 @@ def create_console_app(
             identity=identity,
             devices=devices,
             config=config,
+            mcp_endpoint=mcp_endpoint,
+            mcp_busy_devices=mcp_busy_devices,
             **texts,
         )
 
@@ -375,7 +402,18 @@ def create_console_app(
             }
             for device in manager.list_devices()
         ]
-        return JSONResponse({"status": snapshot, "devices": devices})
+        return JSONResponse(
+            {
+                "status": snapshot,
+                "devices": devices,
+                "mcp_endpoint": "/mcp" if mcp_mounted else None,
+                "mcp_busy_devices": (
+                    mcp_busy_tracker.busy_device_ids()
+                    if mcp_busy_tracker is not None
+                    else []
+                ),
+            }
+        )
 
     @app.get("/devices", response_class=HTMLResponse)
     async def devices_page(

apps/device-host-agent/host_agent/web/mcp.py

@@ -0,0 +1,255 @@
+"""FastMCP server builder for the host-agent MCP endpoint.
+
+Wraps ``api.mcp.tool_handlers(manager=...)`` with:
+
+- Cloud-busy and MCP-busy checks (per-device, fail-fast on conflict).
+- Lazy session-level device lock acquire / renew.
+- Display-status mapping for ``list_devices`` / ``device_status`` so
+  connected-but-idle devices don't appear "busy" (which they do at the
+  ``DeviceManager`` layer because an Appium/WDA session is open).
+
+The builder returns a ``FastMCP`` instance. The caller
+(``create_console_app``) is responsible for wrapping it in
+``BearerAuthMiddleware`` and mounting at ``/mcp``.
+"""
+
+from __future__ import annotations
+
+import contextvars
+from collections.abc import Callable
+from typing import Any
+
+from device.manager import DeviceManager
+from host_agent.mcp_lock import McpBusyTracker
+from host_agent.status import AgentStatusTracker
+from mcp.server.fastmcp import Context, FastMCP
+
+# Tool names that don't target a specific device — skip busy check.
+_NON_DEVICE_TOOLS = frozenset({"list_devices", "device_status"})
+# Tools that report status and should use the display-status mapping.
+_STATUS_TOOLS = frozenset({"list_devices", "device_status"})
+# Name of the wrapper kwarg FastMCP injects the live ``Context`` into.
+# We set ``tool.context_kwarg = _CONTEXT_KWARG`` after swapping the tool's
+# ``fn`` (see ``build_mcp_server``) so FastMCP passes ``ctx`` into our
+# wrapper alongside the validated arguments.
+_CONTEXT_KWARG = "ctx"
+
+
+class McpDeviceBusyError(Exception):
+    """Raised by the wrapper when the target device is held by the cloud
+    assignment path or another MCP session."""
+
+    def __init__(self, device_id: str, busy_owner: str) -> None:
+        super().__init__(f"device {device_id} is busy (held by {busy_owner})")
+        self.device_id = device_id
+        self.busy_owner = busy_owner
+
+
+class FastMcpSdkIncompatibilityError(RuntimeError):
+    """Raised when the FastMCP SDK layout diverges from what this module
+    expects (e.g. ``Tool.fn`` rename or ``Tool.context_kwarg`` removal)."""
+
+
+# contextvars fallback used by tests and any call that originates outside a
+# live FastMCP request lifecycle. Production handlers run inside an MCP
+# request whose context exposes ``request_id`` and the underlying
+# ``session``; ``_current_session_id`` reads from that context first and
+# falls back to this ContextVar.
+_TEST_SESSION_ID: contextvars.ContextVar[str] = contextvars.ContextVar(
+    "_TEST_SESSION_ID", default=""
+)
+
+
+def _current_session_id(ctx: Context | None = None) -> str:
+    """Extract a stable per-MCP-session identifier from the live context.
+
+    The mcp SDK 1.28.1 ``Context`` exposes ``session`` (a long-lived
+    ``ServerSession`` instance per Streamable HTTP session). Its Python
+    object identity (``id(ctx.session)``) is stable across every tool call
+    the same client makes within that session, which is exactly the
+    identity the busy tracker needs to renew leases.
+
+    Falls back to ``_TEST_SESSION_ID`` when no Context is supplied (i.e.
+    when invoked outside a FastMCP request lifecycle, as ``_call_tool_sync``
+    does in tests).
+    """
+    if ctx is not None:
+        session_obj = getattr(ctx, "session", None)
+        if session_obj is not None:
+            return f"mcp_session:{id(session_obj)}"
+    return _TEST_SESSION_ID.get("")
+
+
+def build_mcp_server(
+    *,
+    manager: DeviceManager,
+    mcp_busy_tracker: McpBusyTracker,
+    status_tracker: AgentStatusTracker,
+) -> FastMCP:
+    """Construct the FastMCP server wrapping ``tool_handlers``."""
+    # Imported lazily to keep the package import graph flat.
+    from api.mcp import tool_handlers
+
+    handlers = tool_handlers(manager=manager)
+    server = FastMCP("apex-host-agent")
+
+    for tool_name, raw_handler in handlers.items():
+        wrapped = _wrap_tool(
+            tool_name,
+            raw_handler,
+            mcp_busy_tracker=mcp_busy_tracker,
+            status_tracker=status_tracker,
+        )
+        # Register the raw handler so FastMCP captures its signature (the
+        # MCP wire schema is derived from the function signature). Then
+        # swap ``tool.fn`` for our busy-check / status-mapping wrapper.
+        # Using ``*args, **kwargs`` directly breaks the schema, so we have
+        # to keep the signature and only replace the underlying callable.
+        server._tool_manager.add_tool(  # type: ignore[attr-defined]
+            raw_handler, name=tool_name
+        )
+        try:
+            tool = server._tool_manager._tools[tool_name]  # type: ignore[attr-defined]
+            tool.fn = wrapped
+            # FastMCP injects the live Context into the kwarg named by
+            # ``tool.context_kwarg``. The raw handler doesn't declare one,
+            # so the cached value is None; we override it so the wrapper
+            # receives the Context via its ``ctx`` kwarg.
+            tool.context_kwarg = _CONTEXT_KWARG
+        except AttributeError as exc:
+            raise FastMcpSdkIncompatibilityError(
+                "FastMCP SDK layout changed: cannot swap Tool.fn or set "
+                f"context_kwarg (tool={tool_name!r}). Underlying error: {exc}"
+            ) from exc
+
+    return server
+
+
+def _wrap_tool(
+    tool_name: str,
+    handler: Callable[..., Any],
+    *,
+    mcp_busy_tracker: McpBusyTracker,
+    status_tracker: AgentStatusTracker,
+) -> Callable[..., Any]:
+    def wrapped(*args: Any, **kwargs: Any) -> Any:
+        ctx = kwargs.pop(_CONTEXT_KWARG, None)
+        session_id = _current_session_id(ctx)
+        device_id = kwargs.get("device_id")
+
+        if tool_name in _STATUS_TOOLS:
+            return _with_display_status(handler, status_tracker, *args, **kwargs)
+
+        if device_id is not None and tool_name not in _NON_DEVICE_TOOLS:
+            _check_and_acquire(device_id, session_id, mcp_busy_tracker, status_tracker)
+
+        return handler(*args, **kwargs)
+
+    return wrapped
+
+
+def _check_and_acquire(
+    device_id: str,
+    session_id: str,
+    mcp_busy_tracker: McpBusyTracker,
+    status_tracker: AgentStatusTracker,
+) -> None:
+    cloud_busy = _cloud_busy_device_id(status_tracker)
+    if cloud_busy == device_id:
+        raise McpDeviceBusyError(device_id, "cloud_assignment")
+    if device_id in mcp_busy_tracker.busy_device_ids():
+        existing = next(
+            (
+                lease
+                for lease in mcp_busy_tracker.snapshot()
+                if lease.device_id == device_id
+            ),
+            None,
+        )
+        if existing is not None and existing.session_id != session_id:
+            prefix = existing.session_id[:8]
+            raise McpDeviceBusyError(device_id, f"mcp_session:{prefix}")
+    if not mcp_busy_tracker.acquire(device_id, session_id):
+        # Race: someone else got it between check and acquire.
+        raise McpDeviceBusyError(device_id, "another_session")
+    mcp_busy_tracker.renew(device_id, session_id)
+
+
+def _cloud_busy_device_id(status_tracker: AgentStatusTracker) -> str | None:
+    """Return the device_id currently bound to the cloud assignment, if any."""
+    snap = status_tracker.snapshot()
+    current = snap.get("current_assignment")
+    if not isinstance(current, dict):
+        return None
+    device_id = current.get("device_id")
+    return device_id if isinstance(device_id, str) else None
+
+
+def _with_display_status(
+    handler: Callable[..., Any],
+    status_tracker: AgentStatusTracker,
+    *args: Any,
+    **kwargs: Any,
+) -> Any:
+    busy_device_id = _cloud_busy_device_id(status_tracker)
+    result = handler(*args, **kwargs)
+    if isinstance(result, list):
+        for item in result:
+            if isinstance(item, dict) and "status" in item:
+                item["status"] = _display_status(
+                    item["status"], item.get("id"), busy_device_id
+                )
+        return result
+    if isinstance(result, dict) and "status" in result:
+        result["status"] = _display_status(
+            result["status"], result.get("device_id"), busy_device_id
+        )
+    return result
+
+
+def _display_status(raw: str, device_id: Any, busy_device_id: str | None) -> str:
+    """Mirror ``host_agent.web.app._device_display_status`` semantics.
+
+    A device that's locally "busy" because it's connected-but-idle reports
+    "connected" instead, unless it's the device currently running a cloud
+    assignment (in which case "busy" is the truthful status).
+    """
+    if raw == "busy" and device_id != busy_device_id:
+        return "connected"
+    return raw
+
+
+def _call_tool_sync(
+    server: FastMCP,
+    tool_name: str,
+    arguments: dict[str, Any],
+    *,
+    session_id: str,
+) -> Any:
+    """Test helper: invoke a registered tool synchronously with a forced
+    ``session_id``. Bypasses the HTTP/MCP transport layer (and the live
+    FastMCP Context) so tests don't need an MCP client.
+
+    Walks FastMCP's tool registry (``_tool_manager._tools[tool_name].fn``) —
+    the exact attribute path follows mcp SDK 1.28.1's
+    ``ToolManager._tools`` layout.
+    """
+    token = _TEST_SESSION_ID.set(session_id)
+    try:
+        manager = getattr(server, "_tool_manager", None)
+        if manager is None:
+            raise KeyError(f"tool {tool_name!r} not registered (no tool manager)")
+        registry = getattr(manager, "_tools", None) or getattr(manager, "tools", None)
+        if isinstance(registry, dict):
+            tool = registry.get(tool_name)
+        else:
+            tool = manager.get_tool(tool_name)  # type: ignore[union-attr]
+        if tool is None:
+            raise KeyError(f"tool {tool_name!r} not registered")
+        # FastMCP Tool wraps a callable; our wrappers are sync, so unwrap.
+        fn = getattr(tool, "fn", None) or getattr(tool, "func", None)
+        if fn is None:
+            raise KeyError(f"tool {tool_name!r} has no callable")
+        return fn(**arguments)
+    finally:
+        _TEST_SESSION_ID.reset(token)

apps/device-host-agent/host_agent/web/mcp_auth.py

@@ -0,0 +1,36 @@
+"""Bearer-token auth middleware for the MCP sub-app.
+
+Mounted on the FastMCP ``streamable_http_app()`` (NOT the console FastAPI),
+so cookie-session auth on console routes is unaffected.
+"""
+
+from __future__ import annotations
+
+from starlette.middleware.base import BaseHTTPMiddleware
+from starlette.requests import Request
+from starlette.responses import JSONResponse, Response
+
+from host_agent.mcp_token import McpTokenStore
+
+
+class BearerAuthMiddleware(BaseHTTPMiddleware):
+    def __init__(self, app, token_store: McpTokenStore) -> None:
+        super().__init__(app)
+        self._store = token_store
+
+    async def dispatch(self, request: Request, call_next) -> Response:  # type: ignore[no-untyped-def]
+        header = request.headers.get("Authorization")
+        if not header or not header.lower().startswith("bearer "):
+            return _unauthorized()
+        presented = header.split(" ", 1)[1].strip()
+        if not self._store.verify(presented):
+            return _unauthorized()
+        return await call_next(request)
+
+
+def _unauthorized() -> JSONResponse:
+    return JSONResponse(
+        status_code=401,
+        content={"error": "invalid token"},
+        headers={"WWW-Authenticate": "Bearer"},
+    )

apps/device-host-agent/host_agent/web/templates/dashboard.html

@@ -20,6 +20,24 @@
       <p id="current-assignment">{{ assignment_text }}</p>
       <p id="current-progress">{{ progress_text }}</p>
     </section>
+    <section>
+      <h2>MCP</h2>
+      <table>
+        <tbody>
+          <tr>
+            <td>MCP</td>
+            <td>
+              {% if mcp_endpoint %}
+                endpoint <code>{{ mcp_endpoint }}</code>;
+                {% if mcp_busy_devices %}busy: {{ mcp_busy_devices|join(", ") }}{% else %}idle{% endif %}
+              {% else %}
+                not configured
+              {% endif %}
+            </td>
+          </tr>
+        </tbody>
+      </table>
+    </section>
     <section>
       <h2>Devices</h2>
       <table>

apps/device-host-agent/pyproject.toml

@@ -10,6 +10,7 @@ dependencies = [
     "filelock>=3.0",
     "httpx>=0.27.0",
     "jinja2>=3.1",
+    "mcp>=1.28,<2",
     "uvicorn[standard]>=0.30.0",
 ]
 

apps/device-host-agent/tests/test_app.py

@@ -7,6 +7,7 @@ from datetime import UTC, datetime, timedelta
 
 import httpx
 import pytest
+from starlette.testclient import TestClient
 
 from cloud.internal_api.models import (
     AssignmentModel,
@@ -15,10 +16,23 @@ from cloud.internal_api.models import (
 )
 from device.manager import DeviceManager
 from host_agent.app import HostAgentApplication, create_application
+from host_agent.assignment import AssignmentExecutor
 from host_agent.config import HostAgentConfig
+from host_agent.execution import create_execution_factories
+from host_agent.history import ConsoleHistoryStore
 from host_agent.identity import HostIdentityStore
 from host_agent.instance_lock import InstanceAlreadyRunningError
+from host_agent.local_account import LocalAccountStore
+from host_agent.mcp_lock import McpBusyTracker
+from host_agent.mcp_token import McpTokenStore
+from host_agent.status import AgentStatusTracker
+from host_agent.web.app import create_console_app
+from host_agent.web.auth import SessionManager
+from host_agent.web.mcp import build_mcp_server
+from storage.artifact_store import ArtifactStore
 from storage.device_config import DeviceConfigStore
+from storage.task_metadata import TaskMetadataStore
+from storage.timeline import Timeline
 
 
 def _free_loopback_port() -> int:
@@ -653,6 +667,77 @@ def test_create_application_with_independent_identity_paths_coexist(
         asyncio.run(app_a.client.aclose())
 
 
+def test_create_application_wires_mcp_components(tmp_path, monkeypatch) -> None:
+    """create_application produces a console app with /mcp mounted (auth-protected)
+    and persists the host_mcp_token.json file alongside the identity."""
+    monkeypatch.chdir(tmp_path)
+    config = _config()
+    config_store = DeviceConfigStore(tmp_path / "devices.sqlite3")
+    identity_store = HostIdentityStore(config.identity_path)
+    history_store = ConsoleHistoryStore(
+        tmp_path / "host_console_history.sqlite3",
+        limit=config.console_history_limit,
+    )
+    metadata_store = TaskMetadataStore(db_path=config.task_progress_db_path)
+    timeline = Timeline(ArtifactStore(root=config.task_artifact_dir))
+    status_tracker = AgentStatusTracker()
+
+    application = create_application(
+        config=config,
+        device_config_store=config_store,
+        identity_store=identity_store,
+        manager=DeviceManager(),
+    )
+
+    # Token file must exist after create_application.
+    assert (config.identity_path.parent / "host_mcp_token.json").exists()
+
+    # Heartbeat must hold the in-process McpBusyTracker.
+    assert application.heartbeat.mcp_busy_tracker is not None
+
+    # Build the same console app the production path builds and verify /mcp
+    # is mounted (responds 401, not 404) without a bearer token.
+    mcp_token_store = McpTokenStore(config.identity_path.parent / "host_mcp_token.json")
+    mcp_token_store.load_or_create()
+    mcp_busy_tracker = McpBusyTracker(ttl_seconds=20.0)
+    mcp_server = build_mcp_server(
+        manager=application.heartbeat.manager,
+        mcp_busy_tracker=mcp_busy_tracker,
+        status_tracker=status_tracker,
+    )
+    console_app = create_console_app(
+        config=config,
+        manager=application.heartbeat.manager,
+        config_store=config_store,
+        local_account_store=LocalAccountStore(config.local_account_path),
+        identity_store=identity_store,
+        history_store=history_store,
+        status_tracker=status_tracker,
+        session_manager=SessionManager(ttl_seconds=config.console_session_ttl_seconds),
+        enrollment_client=None,
+        host_client=application.client,
+        metadata_store=metadata_store,
+        timeline=timeline,
+        executor=AssignmentExecutor(
+            create_execution_factories(
+                application.heartbeat.manager,
+                metadata_store=metadata_store,
+                timeline=timeline,
+                host_agent_config=config,
+            ),
+            mcp_busy_tracker=mcp_busy_tracker,
+        ),
+        mcp_server=mcp_server,
+        mcp_token_store=mcp_token_store,
+        mcp_busy_tracker=mcp_busy_tracker,
+    )
+    with TestClient(console_app) as client:
+        resp = client.post("/mcp/")
+        assert resp.status_code == 401  # auth required, not 404
+
+    asyncio.run(application.client.aclose())
+
+
 def test_lock_released_after_run_async_allows_restart(tmp_path, monkeypatch) -> None:
     monkeypatch.chdir(tmp_path)
     identity_path = tmp_path / "host_identity.json"

apps/device-host-agent/tests/test_assignment.py

@@ -154,7 +154,14 @@ def test_workflow_assignment_maps_cancellation_stop_to_cancelled_status() -> Non
             return object() if definition_id == "workflow-a" else None
 
     class FakeWorkflowRunner:
-        def run(self, loaded_definition, device_id: str, *, should_stop=None, stop_reason=None):
+        def run(
+            self,
+            loaded_definition,
+            device_id: str,
+            *,
+            should_stop=None,
+            stop_reason=None,
+        ):
             assert should_stop is not None and should_stop()
             assert stop_reason is not None
             return SimpleNamespace(
@@ -180,6 +187,63 @@ def test_workflow_assignment_maps_cancellation_stop_to_cancelled_status() -> Non
     }
 
 
+def test_execute_fails_fast_when_mcp_session_holds_device() -> None:
+    """Cloud assignment arriving for a device currently held by an MCP
+    session must fail immediately rather than fight for the device."""
+    from host_agent.mcp_lock import McpBusyTracker
+
+    tracker = McpBusyTracker()
+    tracker.acquire("phone-1", "sess-mcp")
+    executor = AssignmentExecutor(
+        _build_factories(),
+        mcp_busy_tracker=tracker,
+    )
+    assignment = _assignment(device_id="phone-1")
+    result = executor.execute(assignment)
+    assert result.status == "failed"
+    assert "MCP" in (result.failure_reason or "")
+
+
+def test_execute_skips_check_when_tracker_is_none() -> None:
+    """Default backward-compat: no tracker → no fail-fast."""
+    executor = AssignmentExecutor(_build_factories())
+    # Without a real workflow store / task runner this test verifies the
+    # entry-point path doesn't raise on the mcp_busy check.
+    # We use a goal + a mock runner factory so execute() runs through.
+    assignment = _assignment()
+    result = executor.execute(assignment)
+    # Should run through normally (not fail on MCP check)
+    assert result.status == "done"
+
+
+def _build_factories() -> ExecutionFactories:
+    """Shared factory fixture used by MCP-hold tests."""
+    received: list[Task] = []
+
+    class FakeTaskRunner:
+        def run(self, task: Task) -> Task:
+            received.append(task)
+            task.status = "completed"
+            return task
+
+    class FakeMetadataStore:
+        def create_task(
+            self,
+            task: Task,
+            *,
+            source_task_id: str | None = None,
+            source_attempt: int | None = None,
+        ) -> None:
+            pass
+
+    return ExecutionFactories(
+        task_runner_factory=lambda: FakeTaskRunner(),  # type: ignore[arg-type,return-value]
+        workflow_runner_factory=lambda: object(),  # type: ignore[arg-type,return-value]
+        workflow_store=object(),  # type: ignore[arg-type]
+        metadata_store=FakeMetadataStore(),  # type: ignore[arg-type]
+    )
+
+
 def test_unknown_workflow_fails_without_running() -> None:
     class FakeWorkflowStore:
         def get_definition(self, definition_id: str):

apps/device-host-agent/tests/test_cli.py

@@ -146,3 +146,21 @@ def test_duplicate_instance_exits_with_clear_error(
     err = capsys.readouterr().err
     assert "another Host Agent instance" in err
     assert str(lock_path) in err
+
+
+def test_mcp_token_subcommand_prints_token(tmp_path, capsys, monkeypatch) -> None:
+    monkeypatch.setenv("HOST_AGENT_IDENTITY_PATH", str(tmp_path / "host_identity.json"))
+    monkeypatch.setenv(
+        "HOST_AGENT_LOCAL_ACCOUNT_PATH", str(tmp_path / "host_local_account.json")
+    )
+    # Also set control plane URL to satisfy config loading
+    monkeypatch.setenv("HOST_AGENT_CONTROL_PLANE_URL", "https://cloud.example")
+    from host_agent.cli import main
+
+    main(["mcp-token"])
+    out = capsys.readouterr().out.strip()
+    assert len(out) >= 40  # token is ~43 chars
+    # Subsequent invocation prints the same token (idempotent).
+    main(["mcp-token"])
+    out2 = capsys.readouterr().out.strip()
+    assert out == out2

apps/device-host-agent/tests/test_client.py

@@ -353,6 +353,60 @@ def test_submit_self_task_does_not_duplicate_when_response_is_lost() -> None:
     assert attempts == 1
 
 
+def test_heartbeat_includes_mcp_busy_device_ids_in_payload() -> None:
+    """When mcp_busy_device_ids is passed, the client sends it in the request."""
+    captured: list[dict[str, object]] = []
+
+    def handler(request: httpx.Request) -> httpx.Response:
+        captured.append(json.loads(request.content))
+        return httpx.Response(
+            200,
+            json={
+                "host_id": "host-a",
+                "accepted_devices": 0,
+                "received_at": "2026-07-12T00:00:00Z",
+            },
+        )
+
+    async def scenario() -> None:
+        async with httpx.AsyncClient(
+            transport=httpx.MockTransport(handler),
+            base_url="https://control.example",
+        ) as http_client:
+            client = HostAgentClient(_config(), http_client=http_client)
+            await client.heartbeat([], mcp_busy_device_ids=["phone-1"])
+
+    asyncio.run(scenario())
+    assert captured[0]["mcp_busy_device_ids"] == ["phone-1"]
+
+
+def test_heartbeat_omits_mcp_busy_device_ids_when_empty() -> None:
+    """Empty list is omitted from the payload (backward compatible)."""
+    captured: list[dict[str, object]] = []
+
+    def handler(request: httpx.Request) -> httpx.Response:
+        captured.append(json.loads(request.content))
+        return httpx.Response(
+            200,
+            json={
+                "host_id": "host-a",
+                "accepted_devices": 0,
+                "received_at": "2026-07-12T00:00:00Z",
+            },
+        )
+
+    async def scenario() -> None:
+        async with httpx.AsyncClient(
+            transport=httpx.MockTransport(handler),
+            base_url="https://control.example",
+        ) as http_client:
+            client = HostAgentClient(_config(), http_client=http_client)
+            await client.heartbeat([], mcp_busy_device_ids=[])
+
+    asyncio.run(scenario())
+    assert "mcp_busy_device_ids" not in captured[0]
+
+
 def test_bootstrap_client_directly_enrolls_and_enrolls_device() -> None:
     requests: list[httpx.Request] = []
     host_attempts = 0

apps/device-host-agent/tests/test_heartbeat.py

@@ -8,6 +8,7 @@ from cloud.internal_api.models import HostGovernancePolicyModel
 from device.manager import DeviceManager
 from host_agent.config import HostAgentConfig
 from host_agent.heartbeat import HeartbeatSynchronizer, build_device_snapshot
+from host_agent.mcp_lock import McpBusyTracker
 from host_agent.policy_cache import HostPolicyCacheStore
 from host_agent.status import AgentStatusTracker
 
@@ -60,7 +61,9 @@ def test_heartbeat_synchronizer_runs_at_configured_interval_until_stopped() -> N
     calls: list[list[str]] = []
 
     class FakeClient:
-        async def heartbeat(self, devices, *, address=None, policy_revision=0):
+        async def heartbeat(
+            self, devices, *, address=None, policy_revision=0, **kwargs
+        ):
             calls.append([device.device_id for device in devices])
             return HeartbeatResponse(
                 host_id="host-a",
@@ -98,7 +101,9 @@ def test_sync_once_notifies_status_tracker_and_on_sync_with_device_count() -> No
     )
 
     class FakeClient:
-        async def heartbeat(self, devices, *, address=None, policy_revision=0):
+        async def heartbeat(
+            self, devices, *, address=None, policy_revision=0, **kwargs
+        ):
             return HeartbeatResponse(
                 host_id="host-a",
                 accepted_devices=len(devices),
@@ -133,7 +138,9 @@ def test_heartbeat_caches_safe_host_policy_and_reuses_its_revision(tmp_path) ->
     revisions: list[int] = []
 
     class UpdatingClient:
-        async def heartbeat(self, devices, *, address=None, policy_revision=0):
+        async def heartbeat(
+            self, devices, *, address=None, policy_revision=0, **kwargs
+        ):
             revisions.append(policy_revision)
             return HeartbeatResponse(
                 host_id="host-a",
@@ -175,6 +182,63 @@ def test_heartbeat_caches_safe_host_policy_and_reuses_its_revision(tmp_path) ->
 
     asyncio.run(scenario())
     assert revisions == [0]
-    assert '"token":' not in (
+    assert '"token":' not in (tmp_path / "host_policy.json").read_text(encoding="utf-8")
-        tmp_path / "host_policy.json"
+
-    ).read_text(encoding="utf-8")
+
+def test_sync_once_passes_mcp_busy_device_ids_to_client() -> None:
+    """When mcp_busy_tracker has a lease, sync_once relays the device_ids."""
+    manager = DeviceManager()
+    tracker = McpBusyTracker()
+    assert tracker.acquire("phone-1", "sess-a")
+    last_kwargs: dict[str, object] = {}
+
+    class FakeClient:
+        async def heartbeat(
+            self, devices, *, address=None, policy_revision=0, **kwargs
+        ):
+            last_kwargs.update(kwargs)
+            return HeartbeatResponse(
+                host_id="host-a",
+                accepted_devices=len(devices),
+                received_at=datetime.now(UTC),
+            )
+
+    async def scenario() -> None:
+        sync = HeartbeatSynchronizer(
+            manager,
+            FakeClient(),  # type: ignore[arg-type]
+            _config(),
+            mcp_busy_tracker=tracker,
+        )
+        await sync.sync_once()
+
+    asyncio.run(scenario())
+    assert last_kwargs.get("mcp_busy_device_ids") == ["phone-1"]
+
+
+def test_sync_once_passes_empty_when_tracker_is_none() -> None:
+    """Default: no tracker → no busy device ids forwarded."""
+    manager = DeviceManager()
+    last_kwargs: dict[str, object] = {}
+
+    class FakeClient:
+        async def heartbeat(
+            self, devices, *, address=None, policy_revision=0, **kwargs
+        ):
+            last_kwargs.update(kwargs)
+            return HeartbeatResponse(
+                host_id="host-a",
+                accepted_devices=len(devices),
+                received_at=datetime.now(UTC),
+            )
+
+    async def scenario() -> None:
+        sync = HeartbeatSynchronizer(
+            manager,
+            FakeClient(),  # type: ignore[arg-type]
+            _config(),
+        )
+        await sync.sync_once()
+
+    asyncio.run(scenario())
+    assert not last_kwargs.get("mcp_busy_device_ids")

apps/device-host-agent/tests/test_mcp_auth.py

@@ -0,0 +1,58 @@
+from __future__ import annotations
+
+from pathlib import Path
+
+from starlette.applications import Starlette
+from starlette.responses import JSONResponse
+from starlette.testclient import TestClient
+
+from host_agent.mcp_token import McpTokenStore
+from host_agent.web.mcp_auth import BearerAuthMiddleware
+
+
+def _make_client(tmp_path: Path) -> tuple[TestClient, str]:
+    store = McpTokenStore(tmp_path / "host_mcp_token.json")
+    token = store.load_or_create().token
+
+    async def hello(request):  # type: ignore[no-untyped-def]
+        return JSONResponse({"ok": True})
+
+    inner = Starlette(routes=[])
+    inner.router.add_route("/", hello, methods=["GET"])
+    wrapped = Starlette()
+    wrapped.add_middleware(BearerAuthMiddleware, token_store=store)
+    wrapped.mount("/", inner)
+    return TestClient(wrapped), token
+
+
+def test_no_header_returns_401(tmp_path: Path) -> None:
+    client, _ = _make_client(tmp_path)
+    resp = client.get("/")
+    assert resp.status_code == 401
+    assert resp.headers["WWW-Authenticate"] == "Bearer"
+    assert resp.json() == {"error": "invalid token"}
+
+
+def test_wrong_token_returns_401(tmp_path: Path) -> None:
+    client, _ = _make_client(tmp_path)
+    resp = client.get("/", headers={"Authorization": "Bearer wrong"})
+    assert resp.status_code == 401
+
+
+def test_correct_token_passes_through(tmp_path: Path) -> None:
+    client, token = _make_client(tmp_path)
+    resp = client.get("/", headers={"Authorization": f"Bearer {token}"})
+    assert resp.status_code == 200
+    assert resp.json() == {"ok": True}
+
+
+def test_non_bearer_scheme_returns_401(tmp_path: Path) -> None:
+    client, token = _make_client(tmp_path)
+    resp = client.get("/", headers={"Authorization": f"Basic {token}"})
+    assert resp.status_code == 401
+
+
+def test_header_case_insensitive(tmp_path: Path) -> None:
+    client, token = _make_client(tmp_path)
+    resp = client.get("/", headers={"authorization": f"Bearer {token}"})
+    assert resp.status_code == 200

apps/device-host-agent/tests/test_mcp_lock.py

@@ -0,0 +1,175 @@
+from __future__ import annotations
+
+import threading
+from datetime import UTC, datetime
+
+from host_agent.mcp_lock import McpBusyTracker
+
+
+def _tracker_with_now() -> tuple[McpBusyTracker, list[datetime]]:
+    times: list[datetime] = []
+
+    def now() -> datetime:
+        return times[-1] if times else datetime(2026, 1, 1, tzinfo=UTC)
+
+    tracker = McpBusyTracker(ttl_seconds=60.0, now=now)
+    return tracker, times
+
+
+def test_acquire_succeeds_on_empty() -> None:
+    tracker, _ = _tracker_with_now()
+    assert tracker.acquire("phone-1", "sess-a") is True
+    assert "phone-1" in tracker.busy_device_ids()
+
+
+def test_acquire_fails_when_held_by_other_session() -> None:
+    tracker, _ = _tracker_with_now()
+    assert tracker.acquire("phone-1", "sess-a") is True
+    assert tracker.acquire("phone-1", "sess-b") is False
+
+
+def test_acquire_is_idempotent_for_same_session() -> None:
+    tracker, _ = _tracker_with_now()
+    assert tracker.acquire("phone-1", "sess-a") is True
+    # Same session re-acquiring is allowed (acts as renew).
+    assert tracker.acquire("phone-1", "sess-a") is True
+
+
+def test_renew_refreshes_last_seen() -> None:
+    tracker, times = _tracker_with_now()
+    times.append(datetime(2026, 1, 1, 12, 0, tzinfo=UTC))
+    tracker.acquire("phone-1", "sess-a")
+    initial = tracker.snapshot()[0]
+    times.append(datetime(2026, 1, 1, 12, 0, 30, tzinfo=UTC))
+    assert tracker.renew("phone-1", "sess-a") is True
+    refreshed = tracker.snapshot()[0]
+    assert refreshed.last_seen_at > initial.last_seen_at
+
+
+def test_renew_fails_when_held_by_other() -> None:
+    tracker, _ = _tracker_with_now()
+    tracker.acquire("phone-1", "sess-a")
+    assert tracker.renew("phone-1", "sess-b") is False
+
+
+def test_release_returns_freed_device_ids() -> None:
+    tracker, _ = _tracker_with_now()
+    tracker.acquire("phone-1", "sess-a")
+    tracker.acquire("phone-2", "sess-a")
+    freed = tracker.release("sess-a")
+    assert sorted(freed) == ["phone-1", "phone-2"]
+    assert tracker.busy_device_ids() == []
+
+
+def test_release_only_frees_caller_session() -> None:
+    tracker, _ = _tracker_with_now()
+    tracker.acquire("phone-1", "sess-a")
+    tracker.acquire("phone-1", "sess-b")  # fails
+    freed = tracker.release("sess-b")
+    assert freed == []
+    assert "phone-1" in tracker.busy_device_ids()
+
+
+def test_ttl_sweeps_expired_leases() -> None:
+    tracker, times = _tracker_with_now()
+    times.append(datetime(2026, 1, 1, 12, 0, tzinfo=UTC))
+    tracker.acquire("phone-1", "sess-a")
+    # Advance past TTL without renew.
+    times.append(datetime(2026, 1, 1, 12, 1, 1, tzinfo=UTC))  # 61s later
+    assert tracker.busy_device_ids() == []
+
+
+def test_renew_after_ttl_tolerates_same_session() -> None:
+    """Scene 10: lease expired but session_id matches -> re-acquire."""
+    tracker, times = _tracker_with_now()
+    times.append(datetime(2026, 1, 1, 12, 0, tzinfo=UTC))
+    tracker.acquire("phone-1", "sess-a")
+    times.append(datetime(2026, 1, 1, 12, 1, 1, tzinfo=UTC))  # expired
+    # renew from the same session should succeed (re-acquire).
+    assert tracker.renew("phone-1", "sess-a") is True
+    assert "phone-1" in tracker.busy_device_ids()
+
+
+def test_snapshot_matches_busy_device_ids() -> None:
+    tracker, _ = _tracker_with_now()
+    tracker.acquire("phone-1", "sess-a")
+    tracker.acquire("phone-2", "sess-a")
+    snap = tracker.snapshot()
+    assert {lease.device_id for lease in snap} == set(tracker.busy_device_ids())
+
+
+def test_wait_until_usable_succeeds_when_free() -> None:
+    tracker, _ = _tracker_with_now()
+    ok = tracker.wait_until_usable("phone-1", "sess-a", timeout=1.0, poll_interval=0.01)
+    assert ok is True
+    assert "phone-1" in tracker.busy_device_ids()
+
+
+def test_wait_until_usable_returns_false_on_timeout() -> None:
+    tracker, _ = _tracker_with_now()
+    tracker.acquire("phone-1", "sess-a")
+    ok = tracker.wait_until_usable("phone-1", "sess-b", timeout=0.1, poll_interval=0.02)
+    assert ok is False
+
+
+def test_wait_until_usable_blocks_then_succeeds_when_released() -> None:
+    tracker, _ = _tracker_with_now()
+    tracker.acquire("phone-1", "sess-a")
+
+    def releaser() -> None:
+        import time
+
+        time.sleep(0.05)
+        tracker.release("sess-a")
+
+    t = threading.Thread(target=releaser)
+    t.start()
+    try:
+        ok = tracker.wait_until_usable(
+            "phone-1", "sess-b", timeout=2.0, poll_interval=0.02
+        )
+        assert ok is True
+    finally:
+        t.join()
+
+
+def test_wait_until_usable_blocks_then_fails_when_cloud_remains_busy() -> None:
+    tracker, _ = _tracker_with_now()
+    ok = tracker.wait_until_usable(
+        "phone-1",
+        "sess-a",
+        timeout=0.1,
+        poll_interval=0.02,
+        cloud_busy_check=lambda: True,
+    )
+    assert ok is False
+    assert tracker.busy_device_ids() == []
+
+
+def test_default_ttl_is_20_seconds() -> None:
+    """The McpBusyTracker default TTL is 20s: short enough to recover from a
+    dead MCP session within a heartbeat interval without an explicit release
+    callback (mcp SDK 1.28.1 has no per-session shutdown hook), but long
+    enough that an actively-busy session does not lose its lease during
+    normal operator pauses."""
+    tracker = McpBusyTracker()
+    assert tracker._ttl == 20.0
+
+
+def test_default_ttl_recovers_dead_session_within_one_window() -> None:
+    """With the 20s default, a session that never renews its lease is
+    reaped within one TTL window on the next read. This is the
+    concrete fallback behavior for I1 (no FastMCP session-end hook)."""
+    times: list[datetime] = []
+
+    def now() -> datetime:
+        return times[-1] if times else datetime(2026, 1, 1, tzinfo=UTC)
+
+    tracker = McpBusyTracker(now=now)  # default 20s TTL
+    times.append(datetime(2026, 1, 1, 12, 0, tzinfo=UTC))
+    assert tracker.acquire("phone-1", "dead-session") is True
+    # No renew: advance 21s. Lease should be swept on next read.
+    times.append(datetime(2026, 1, 1, 12, 0, 21, tzinfo=UTC))
+    assert tracker.busy_device_ids() == []
+    # New session can now acquire cleanly (no stale-busy contamination).
+    assert tracker.acquire("phone-1", "new-session") is True

apps/device-host-agent/tests/test_mcp_token.py

@@ -0,0 +1,107 @@
+from __future__ import annotations
+
+import json
+import os
+import stat
+import sys
+from datetime import datetime
+from pathlib import Path
+
+import pytest
+
+from host_agent.mcp_token import McpToken, McpTokenStore, McpTokenStoreError
+
+
+def test_load_or_create_generates_when_missing(tmp_path: Path) -> None:
+    store = McpTokenStore(tmp_path / "host_mcp_token.json")
+    token = store.load_or_create()
+    assert token.version == 1
+    assert len(token.token) >= 40  # secrets.token_urlsafe(32) -> ~43 chars
+    assert isinstance(token.created_at, datetime)
+    # File now exists.
+    assert (tmp_path / "host_mcp_token.json").exists()
+
+
+def test_load_or_create_is_idempotent(tmp_path: Path) -> None:
+    store = McpTokenStore(tmp_path / "host_mcp_token.json")
+    first = store.load_or_create()
+    second = McpTokenStore(tmp_path / "host_mcp_token.json").load_or_create()
+    assert first.token == second.token
+
+
+def test_load_or_create_writes_json_schema(tmp_path: Path) -> None:
+    path = tmp_path / "host_mcp_token.json"
+    McpTokenStore(path).load_or_create()
+    data = json.loads(path.read_text())
+    assert set(data) == {"version", "token", "created_at"}
+    assert data["version"] == 1
+    assert isinstance(data["token"], str)
+    # created_at is ISO 8601.
+    datetime.fromisoformat(data["created_at"])
+
+
+@pytest.mark.skipif(sys.platform == "win32", reason="POSIX perms only")
+def test_load_or_create_sets_posix_permissions(tmp_path: Path) -> None:
+    path = tmp_path / "host_mcp_token.json"
+    McpTokenStore(path).load_or_create()
+    mode = stat.S_IMODE(os.fstat(os.open(path, os.O_RDONLY)).st_mode)
+    assert mode == 0o600
+
+
+def test_verify_accepts_correct_token(tmp_path: Path) -> None:
+    store = McpTokenStore(tmp_path / "host_mcp_token.json")
+    token = store.load_or_create()
+    assert store.verify(token.token) is True
+
+
+def test_verify_rejects_wrong_token(tmp_path: Path) -> None:
+    store = McpTokenStore(tmp_path / "host_mcp_token.json")
+    store.load_or_create()
+    assert store.verify("wrong") is False
+
+
+def test_load_or_create_raises_on_corrupt_json(tmp_path: Path) -> None:
+    path = tmp_path / "host_mcp_token.json"
+    path.write_text("{not valid json")
+    with pytest.raises(McpTokenStoreError):
+        McpTokenStore(path).load_or_create()
+
+
+@pytest.mark.skipif(sys.platform == "win32", reason="POSIX chmod enforcement only")
+def test_load_or_create_raises_on_unwritable_dir(tmp_path: Path) -> None:
+    unwritable = tmp_path / "ro"
+    unwritable.mkdir()
+    os.chmod(unwritable, 0o500)  # r-x for owner
+    try:
+        with pytest.raises(McpTokenStoreError):
+            McpTokenStore(unwritable / "host_mcp_token.json").load_or_create()
+    finally:
+        os.chmod(unwritable, 0o700)  # restore so cleanup works
+
+
+@pytest.mark.skipif(
+    sys.platform == "win32",
+    reason="POSIX atomic-rename semantics only",
+)
+def test_load_or_create_concurrent_calls_do_not_corrupt(
+    tmp_path: Path,
+) -> None:
+    """Two store instances racing to create: both end up reading the same token."""
+    import threading
+
+    path = tmp_path / "host_mcp_token.json"
+    results: list[McpToken] = []
+    barrier = threading.Barrier(2)
+
+    def worker() -> None:
+        barrier.wait()
+        store = McpTokenStore(path)
+        results.append(store.load_or_create())
+
+    threads = [threading.Thread(target=worker) for _ in range(2)]
+    for t in threads:
+        t.start()
+    for t in threads:
+        t.join()
+    assert len(results) == 2
+    assert results[0].token == results[1].token

apps/device-host-agent/tests/test_web_app.py

@@ -6,6 +6,7 @@ from datetime import UTC, datetime
 from typing import Any
 
 from fastapi.testclient import TestClient
+from mcp.server.fastmcp import FastMCP
 
 from cloud.internal_api.models import AssignmentModel
 from core.models import Task
@@ -15,9 +16,12 @@ from host_agent.config import HostAgentConfig
 from host_agent.history import ConsoleHistoryStore
 from host_agent.identity import HostIdentityStore
 from host_agent.local_account import LocalAccountStore
+from host_agent.mcp_lock import McpBusyTracker
+from host_agent.mcp_token import McpTokenStore
 from host_agent.status import AgentStatusTracker
 from host_agent.web.app import SESSION_COOKIE_NAME, create_console_app
 from host_agent.web.auth import SessionManager
+from host_agent.web.mcp import build_mcp_server
 from storage.device_config import DeviceConfigStore
 from storage.task_metadata import TaskMetadataStore
 
@@ -34,6 +38,9 @@ def _build_client(
     submit_self_task: TaskSubmissionCallable | None = None,
     cancel_task: TaskCancellationCallable | None = None,
     include_metadata_store: bool = True,
+    mcp_server: FastMCP | None = None,
+    mcp_token_store: McpTokenStore | None = None,
+    mcp_busy_tracker: McpBusyTracker | None = None,
 ) -> tuple[TestClient, dict]:
     config = HostAgentConfig(
         control_plane_url="https://control.example",
@@ -68,6 +75,9 @@ def _build_client(
         submit_self_task=submit_self_task,
         cancel_task=cancel_task,
         metadata_store=metadata_store,
+        mcp_server=mcp_server,
+        mcp_token_store=mcp_token_store,
+        mcp_busy_tracker=mcp_busy_tracker,
     )
     client = TestClient(app)
     context = {
@@ -823,9 +833,7 @@ def _seed_local_task(
     source_task_id: str | None = "cloud-task-1",
 ) -> str:
     task = Task(goal="open settings", device_id="dev-1", status=status)
-    metadata_store.create_task(
+    metadata_store.create_task(task, source_task_id=source_task_id, source_attempt=1)
-        task, source_task_id=source_task_id, source_attempt=1
-    )
     return task.id
 
 
@@ -959,3 +967,131 @@ def test_cancel_task_without_csrf_token_is_rejected(tmp_path) -> None:
 
     assert response.status_code == 403
     assert captured == {}
+
+
+# ---------------------------------------------------------------------------
+# MCP mount + /api/status fields + dashboard row
+# ---------------------------------------------------------------------------
+
+
+def _build_mcp_components(tmp_path) -> tuple[FastMCP, McpTokenStore, McpBusyTracker]:
+    manager = DeviceManager()
+    status_tracker = AgentStatusTracker()
+    tracker = McpBusyTracker()
+    token_store = McpTokenStore(tmp_path / "host_mcp_token.json")
+    server = build_mcp_server(
+        manager=manager,
+        mcp_busy_tracker=tracker,
+        status_tracker=status_tracker,
+    )
+    return server, token_store, tracker
+
+
+def test_console_app_mounts_mcp_when_all_components_provided(tmp_path) -> None:
+    server, token_store, tracker = _build_mcp_components(tmp_path)
+    client, _ = _build_client(
+        tmp_path,
+        mcp_server=server,
+        mcp_token_store=token_store,
+        mcp_busy_tracker=tracker,
+    )
+    # Without auth, the bearer middleware should respond 401 — not 404.
+    resp = client.post("/mcp/", json={"jsonrpc": "2.0", "method": "ping", "id": 1})
+    assert resp.status_code != 404
+
+
+def test_console_app_does_not_mount_mcp_when_components_missing(tmp_path) -> None:
+    client, _ = _build_client(tmp_path)
+    resp = client.post("/mcp/", json={"jsonrpc": "2.0", "method": "ping", "id": 1})
+    assert resp.status_code == 404
+
+
+def test_api_status_includes_mcp_busy_devices(tmp_path) -> None:
+    server, token_store, tracker = _build_mcp_components(tmp_path)
+    # Acquire a lease without going through HTTP — tracker exposes a direct API.
+    tracker.acquire("phone-1", "test-session")
+    client, _ = _build_client(
+        tmp_path,
+        mcp_server=server,
+        mcp_token_store=token_store,
+        mcp_busy_tracker=tracker,
+    )
+    _login(client)
+
+    response = client.get("/api/status")
+    assert response.status_code == 200
+    body = response.json()
+    assert "mcp_busy_devices" in body
+    assert "phone-1" in body["mcp_busy_devices"]
+    assert body["mcp_endpoint"] == "/mcp"
+
+
+def test_api_status_omits_mcp_fields_when_components_missing(tmp_path) -> None:
+    client, _ = _build_client(tmp_path)
+    _login(client)
+
+    response = client.get("/api/status")
+    assert response.status_code == 200
+    body = response.json()
+    assert body["mcp_busy_devices"] == []
+    assert body["mcp_endpoint"] is None
+
+
+def test_dashboard_renders_mcp_status_row(tmp_path) -> None:
+    server, token_store, tracker = _build_mcp_components(tmp_path)
+    tracker.acquire("phone-1", "test-session")
+    client, _ = _build_client(
+        tmp_path,
+        mcp_server=server,
+        mcp_token_store=token_store,
+        mcp_busy_tracker=tracker,
+    )
+    _login(client)
+
+    response = client.get("/")
+    assert response.status_code == 200
+    text = response.text
+    assert "<td>MCP</td>" in text
+    assert "/mcp" in text
+    assert "phone-1" in text
+
+
+def test_dashboard_renders_mcp_not_configured_when_components_missing(
+    tmp_path,
+) -> None:
+    client, _ = _build_client(tmp_path)
+    _login(client)
+
+    response = client.get("/")
+    assert response.status_code == 200
+    text = response.text
+    assert "<td>MCP</td>" in text
+    assert "not configured" in text
+
+
+def test_mcp_endpoint_unauthorized_without_bearer_token(tmp_path) -> None:
+    server, token_store, tracker = _build_mcp_components(tmp_path)
+    client, _ = _build_client(
+        tmp_path,
+        mcp_server=server,
+        mcp_token_store=token_store,
+        mcp_busy_tracker=tracker,
+    )
+    resp = client.post("/mcp/", json={"jsonrpc": "2.0", "method": "ping", "id": 1})
+    assert resp.status_code == 401
+
+
+def test_mcp_endpoint_rejects_invalid_bearer_token(tmp_path) -> None:
+    server, token_store, tracker = _build_mcp_components(tmp_path)
+    client, _ = _build_client(
+        tmp_path,
+        mcp_server=server,
+        mcp_token_store=token_store,
+        mcp_busy_tracker=tracker,
+    )
+    resp = client.post(
+        "/mcp/",
+        headers={"Authorization": "Bearer not-the-real-token"},
+        json={"jsonrpc": "2.0", "method": "ping", "id": 1},
+    )
+    assert resp.status_code == 401

apps/device-host-agent/tests/test_web_mcp.py

@@ -0,0 +1,415 @@
+from __future__ import annotations
+
+from datetime import UTC, datetime
+from typing import Any
+
+import pytest
+
+from cloud.internal_api.models import AssignmentModel
+from device.manager import DeviceManager
+from driver.base import Driver
+from host_agent.mcp_lock import McpBusyTracker
+from host_agent.status import AgentStatusTracker
+from host_agent.web.mcp import (
+    McpDeviceBusyError,
+    _call_tool_sync,
+    _current_session_id,
+    build_mcp_server,
+)
+from mcp.server.fastmcp import Context
+from mcp.shared.context import RequestContext
+
+
+class _FakeDriver(Driver):
+    """Minimal driver. connect/screenshot/tap are exercised; remaining abstract
+    methods are stubbed to satisfy Driver's ABC contract."""
+
+    def __init__(self) -> None:
+        self.taps: list[tuple[float, float]] = []
+
+    def connect(self) -> None:
+        return None
+
+    def disconnect(self) -> None:
+        return None
+
+    def screenshot(self) -> bytes:
+        return b"fake"
+
+    def tap(self, x: float, y: float) -> None:
+        self.taps.append((x, y))
+
+    def long_press(self, x: float, y: float, duration_ms: int = 1200) -> None:
+        return None
+
+    def swipe(
+        self,
+        start_x: float,
+        start_y: float,
+        end_x: float,
+        end_y: float,
+        duration_ms: int = 500,
+    ) -> None:
+        return None
+
+    def swipe_path(
+        self, waypoints: list[tuple[float, float]], duration_ms: int
+    ) -> None:
+        return None
+
+    def double_tap(self, x: float, y: float, interval_ms: int = 80) -> None:
+        return None
+
+    def input(self, text: str) -> None:
+        return None
+
+    def launch(self, app_id: str) -> None:
+        return None
+
+    def terminate(self, app_id: str) -> None:
+        return None
+
+    def tree(self) -> Any:
+        return None
+
+    def home(self) -> None:
+        return None
+
+    def lock(self) -> None:
+        return None
+
+    def unlock(self) -> None:
+        return None
+
+
+def _make_manager_with_device(device_id: str = "phone-1") -> DeviceManager:
+    manager = DeviceManager()
+    manager.register_device(
+        device_id=device_id,
+        driver_factory=lambda: _FakeDriver(),
+        name=device_id,
+    )
+    manager.connect(device_id)
+    return manager
+
+
+def test_build_mcp_server_returns_fastmcp_instance() -> None:
+    from mcp.server.fastmcp import FastMCP
+
+    manager = _make_manager_with_device()
+    tracker = McpBusyTracker()
+    status = AgentStatusTracker()
+    server = build_mcp_server(
+        manager=manager, mcp_busy_tracker=tracker, status_tracker=status
+    )
+    assert isinstance(server, FastMCP)
+
+
+def test_call_tool_succeeds_when_device_is_free() -> None:
+    manager = _make_manager_with_device()
+    tracker = McpBusyTracker()
+    status = AgentStatusTracker()
+    server = build_mcp_server(
+        manager=manager, mcp_busy_tracker=tracker, status_tracker=status
+    )
+    result = _call_tool_sync(
+        server, "take_screenshot", {"device_id": "phone-1"}, session_id="sess-a"
+    )
+    assert result["ok"] is True
+    assert "phone-1" in tracker.busy_device_ids()
+
+
+def test_call_tool_fails_when_cloud_uses_device() -> None:
+    """AgentStatusTracker.current_assignment.device_id matches -> busy."""
+    manager = _make_manager_with_device()
+    tracker = McpBusyTracker()
+    status = AgentStatusTracker()
+    status.mark_assignment_started(
+        AssignmentModel(
+            task_id="t1",
+            attempt=1,
+            lease_id="l1",
+            lease_expires_at=datetime.now(UTC),
+            host_id="h1",
+            device_id="phone-1",
+            goal="cloud task",
+        )
+    )
+    server = build_mcp_server(
+        manager=manager, mcp_busy_tracker=tracker, status_tracker=status
+    )
+    with pytest.raises(McpDeviceBusyError) as exc:
+        _call_tool_sync(
+            server,
+            "take_screenshot",
+            {"device_id": "phone-1"},
+            session_id="sess-a",
+        )
+    assert exc.value.device_id == "phone-1"
+    assert exc.value.busy_owner == "cloud_assignment"
+
+
+def test_call_tool_fails_when_another_mcp_session_holds_device() -> None:
+    manager = _make_manager_with_device()
+    tracker = McpBusyTracker()
+    status = AgentStatusTracker()
+    # Pre-acquire as a different session.
+    tracker.acquire("phone-1", "sess-other")
+    server = build_mcp_server(
+        manager=manager, mcp_busy_tracker=tracker, status_tracker=status
+    )
+    with pytest.raises(McpDeviceBusyError) as exc:
+        _call_tool_sync(
+            server,
+            "take_screenshot",
+            {"device_id": "phone-1"},
+            session_id="sess-a",
+        )
+    assert exc.value.busy_owner.startswith("mcp_session:")
+
+
+def test_call_tool_renews_when_same_session_already_holds() -> None:
+    manager = _make_manager_with_device()
+    tracker = McpBusyTracker()
+    status = AgentStatusTracker()
+    server = build_mcp_server(
+        manager=manager, mcp_busy_tracker=tracker, status_tracker=status
+    )
+    _call_tool_sync(
+        server, "take_screenshot", {"device_id": "phone-1"}, session_id="sess-a"
+    )
+    # Second call from the same session should succeed.
+    result = _call_tool_sync(
+        server, "take_screenshot", {"device_id": "phone-1"}, session_id="sess-a"
+    )
+    assert result["ok"] is True
+
+
+def test_list_devices_uses_display_status() -> None:
+    """Connected-but-idle devices report as 'connected', not 'busy'."""
+    manager = _make_manager_with_device()
+    tracker = McpBusyTracker()
+    status = AgentStatusTracker()
+    server = build_mcp_server(
+        manager=manager, mcp_busy_tracker=tracker, status_tracker=status
+    )
+    result = _call_tool_sync(server, "list_devices", {}, session_id="sess-a")
+    assert isinstance(result, list)
+    assert result[0]["status"] == "connected"
+
+
+def test_unknown_device_returns_semantic_error_dict() -> None:
+    """take_screenshot against an unknown device returns the api-errors semantic
+    error dict (``ok=False, error="device not found"``) rather than raising.
+
+    Note: this test adapts the brief's exception-assertion semantics to the
+    actual behavior of ``call_with_semantic_errors`` in ``api/errors.py`` —
+    the brief's expectation that an exception is raised here is incorrect for
+    the current handler implementation."""
+    manager = _make_manager_with_device()
+    tracker = McpBusyTracker()
+    status = AgentStatusTracker()
+    server = build_mcp_server(
+        manager=manager, mcp_busy_tracker=tracker, status_tracker=status
+    )
+    result = _call_tool_sync(
+        server,
+        "take_screenshot",
+        {"device_id": "does-not-exist"},
+        session_id="sess-a",
+    )
+    assert isinstance(result, dict)
+    assert result["ok"] is False
+    assert "device" in result["error"].lower()
+
+
+def test_manager_required_for_build_mcp_server() -> None:
+    """Reinforces D12 — build_mcp_server requires manager as keyword-only."""
+    import inspect
+
+    sig = inspect.signature(build_mcp_server)
+    assert sig.parameters["manager"].kind == inspect.Parameter.KEYWORD_ONLY
+
+
+def _fake_ctx(session_obj: object) -> Context:
+    """Build a Context whose ``session`` attribute returns ``session_obj``.
+
+    Context's ``session`` is a property backed by ``request_context.session``;
+    we construct a minimal ``RequestContext`` and set it as the private
+    ``_request_context`` field. The pydantic public API doesn't expose a
+    setter for ``session``, so we use ``object.__setattr__`` on the private
+    backing field.
+    """
+    ctx = Context.model_construct()
+    request_ctx = RequestContext(
+        request_id="req-test",
+        meta=None,
+        session=session_obj,
+        lifespan_context=None,
+    )
+    object.__setattr__(ctx, "_request_context", request_ctx)
+    return ctx
+
+
+def test_current_session_id_is_stable_across_calls_same_session() -> None:
+    """Production-path identity: two tool calls from the same MCP session
+    must yield the same session_id so the busy tracker can renew the lease.
+
+    This exercises the ``Context.session`` code path (NOT the
+    ``_TEST_SESSION_ID`` fallback used by ``_call_tool_sync``)."""
+    sentinel_session = object()
+    ctx = _fake_ctx(sentinel_session)
+    first = _current_session_id(ctx)
+    second = _current_session_id(ctx)
+    assert first == second
+    assert first.startswith("mcp_session:")
+    # Object identity of the underlying ServerSession is the key — verifies
+    # we use id(ctx.session) rather than e.g. ctx.request_id.
+    assert first == f"mcp_session:{id(sentinel_session)}"
+
+
+def test_current_session_id_differs_across_sessions() -> None:
+    """Two different MCP sessions (distinct ServerSession objects) must
+    produce distinct session_ids so the busy tracker can isolate them."""
+    sess_a = object()
+    sess_b = object()
+    assert _current_session_id(_fake_ctx(sess_a)) != _current_session_id(
+        _fake_ctx(sess_b)
+    )
+
+
+def test_current_session_id_falls_back_when_no_context() -> None:
+    """When no Context is available (e.g. outside a FastMCP request lifecycle,
+    or via ``_call_tool_sync`` which omits the ctx kwarg), the test
+    contextvars override provides the session_id."""
+    token = None
+    try:
+        from host_agent.web import mcp as mcp_mod
+
+        token = mcp_mod._TEST_SESSION_ID.set("test-session-xyz")
+        assert _current_session_id(None) == "test-session-xyz"
+    finally:
+        if token is not None:
+            from host_agent.web import mcp as mcp_mod
+
+            mcp_mod._TEST_SESSION_ID.reset(token)
+
+
+def test_wrapped_tool_accepts_context_kwarg() -> None:
+    """The wrapper registered on FastMCP must declare a ``ctx`` parameter so
+    FastMCP injects the live Context (and ``tool.context_kwarg`` is set to
+    ``"ctx"``). Without this, FastMCP never injects context and we fall
+    back to the empty test default — the production bug this PR fixes."""
+    manager = _make_manager_with_device()
+    tracker = McpBusyTracker()
+    status = AgentStatusTracker()
+    server = build_mcp_server(
+        manager=manager, mcp_busy_tracker=tracker, status_tracker=status
+    )
+    tool_manager = server._tool_manager  # type: ignore[attr-defined]
+    tool = tool_manager.get_tool("take_screenshot")
+    assert tool is not None
+    assert tool.context_kwarg == "ctx"
+
+
+def test_busy_error_wire_shape_is_calltoolresult_iserror() -> None:
+    """Regression test for spec §7 — busy errors must be visible on the wire.
+
+    mcp SDK 1.28.1's ``Tool.run`` wraps every non-``UrlElicitationRequiredError``
+    exception (including ``McpError`` and our ``McpDeviceBusyError``) into
+    ``ToolError`` (see ``mcp/server/fastmcp/tools/base.py``). The lowlevel
+    ``call_tool`` handler then builds a ``CallToolResult(isError=True,
+    content=[TextContent(...)])`` (see
+    ``mcp/server/lowlevel/server.py::_make_error_result``). There is no public
+    path that surfaces JSON-RPC ``-32000`` + structured ``data.busy_owner`` from
+    a tool call site — the SDK's wire contract for tool errors is the
+    ``isError=true`` flag plus text content. This test pins the wire shape so
+    any future SDK upgrade that exposes a true JSON-RPC error path is caught."""
+    import asyncio
+
+    import mcp.types as types
+    from mcp.server.fastmcp import FastMCP
+    from mcp.server.fastmcp.exceptions import ToolError
+
+    manager = _make_manager_with_device()
+    tracker = McpBusyTracker()
+    status = AgentStatusTracker()
+    tracker.acquire("phone-1", "sess-other")  # different session holds the device
+
+    server: FastMCP = build_mcp_server(
+        manager=manager, mcp_busy_tracker=tracker, status_tracker=status
+    )
+    tool = server._tool_manager.get_tool("take_screenshot")  # type: ignore[attr-defined]
+    assert tool is not None
+
+    sentinel_session = object()
+    ctx = _fake_ctx(sentinel_session)
+
+    with pytest.raises(ToolError) as tool_exc:
+        asyncio.run(tool.run({"device_id": "phone-1"}, context=ctx))
+
+    # ToolError text carries the original exception message verbatim,
+    # which is what the lowlevel handler copies into TextContent.
+    message = str(tool_exc.value)
+    assert "phone-1" in message
+    assert "busy" in message
+    assert "mcp_session:sess-oth" in message  # truncated busy_owner
+
+    # The lowlevel handler converts any exception into a CallToolResult
+    # with isError=True (mcp SDK 1.28.1 — not a JSON-RPC error envelope).
+    # We invoke the SDK helper directly to lock the wire contract.
+    from mcp.server.lowlevel.server import Server as LowlevelServer
+
+    lowlevel = LowlevelServer("test-lowlevel")
+    error_result = lowlevel._make_error_result(message)  # type: ignore[attr-defined]
+    inner = error_result.root
+    assert isinstance(inner, types.CallToolResult)
+    assert inner.isError is True
+    assert len(inner.content) == 1
+    text_block = inner.content[0]
+    assert isinstance(text_block, types.TextContent)
+    assert text_block.text == message
+    # And confirm the wire shape is NOT a JSON-RPC error envelope — that
+    # would require code=-32000 + data.busy_owner, which is not exposed
+    # in mcp SDK 1.28.1 for tool-call errors.
+    assert not hasattr(inner, "code")
+    assert inner.structuredContent is None
+
+
+def test_busy_error_text_includes_cloud_assignment_owner() -> None:
+    """Same wire-shape test for the cloud_assignment branch — verifies the
+    human-readable busy_owner value (the only place to surface it given the
+    SDK forces tool errors into CallToolResult.isError=true) is correct."""
+    import asyncio
+
+    from mcp.server.fastmcp.exceptions import ToolError
+
+    manager = _make_manager_with_device()
+    tracker = McpBusyTracker()
+    status = AgentStatusTracker()
+    status.mark_assignment_started(
+        AssignmentModel(
+            task_id="t1",
+            attempt=1,
+            lease_id="l1",
+            lease_expires_at=datetime.now(UTC),
+            host_id="h1",
+            device_id="phone-1",
+            goal="cloud task",
+        )
+    )
+
+    server = build_mcp_server(
+        manager=manager, mcp_busy_tracker=tracker, status_tracker=status
+    )
+    tool = server._tool_manager.get_tool("take_screenshot")  # type: ignore[attr-defined]
+    assert tool is not None
+
+    sentinel_session = object()
+    ctx = _fake_ctx(sentinel_session)
+
+    with pytest.raises(ToolError) as tool_exc:
+        asyncio.run(tool.run({"device_id": "phone-1"}, context=ctx))
+    assert "cloud_assignment" in str(tool_exc.value)
+    assert "phone-1" in str(tool_exc.value)
+    assert "busy" in str(tool_exc.value)

docs/MACOS_IPHONE_SETUP.md

@@ -527,6 +527,20 @@ Appium server 默认使用 4723；WDA 通常使用 8100。多设备必须为每
 input、launch 和 UI tree 验证基础控制，再单独处理 PaddleOCR/PaddlePaddle 的 macOS
 wheel 与 Apple Silicon 兼容性。
 
+## MCP server (Hermes Agent integration)
+
+Host-agent now exposes an MCP server on the same port as the local
+console (`127.0.0.1:8765/mcp`). To drive your iPhone from Hermes Agent
+or any MCP-compatible client:
+
+1. Start host-agent normally.
+2. Get the bearer token: `device-host-agent mcp-token`.
+3. Configure Hermes per `docs/MCP_INTEGRATION.md`.
+
+The MCP path reuses the same WDA session that the cloud worker uses.
+Per-device locking prevents both sides from driving the same device at
+once; see `docs/MCP_INTEGRATION.md` for the full concurrency model.
+
 ## 12. 完成检查表
 
 - [ ] Xcode 能看到已解锁的 iPhone。

docs/MCP_INTEGRATION.md

@@ -0,0 +1,125 @@
+# Host-Agent MCP Server Integration
+
+The host-agent process exposes a Streamable HTTP MCP server on the same
+port as the local console (default `127.0.0.1:8765`), at path `/mcp`. This
+lets any MCP-compatible client — Hermes Agent, Claude Desktop, custom
+scripts using the `mcp` Python SDK — drive devices directly through the
+same `DeviceManager` the cloud worker uses.
+
+## Prerequisites
+
+- Host-agent built from this repo (see `docs/MACOS_IPHONE_SETUP.md`).
+- An MCP client that supports the Streamable HTTP transport (mcp SDK
+  1.20+ on the client side).
+
+## Get the bearer token
+
+The first time host-agent starts after this feature ships, it generates
+a random bearer token and writes it to:
+
+    <identity_path.parent>/host_mcp_token.json
+
+(Default: `tasks/host_mcp_token.json` next to `host_identity.json`.)
+
+To print it for copy/paste:
+
+    device-host-agent mcp-token
+
+To rotate: delete the file and restart host-agent. Old tokens stop
+working immediately.
+
+## Hermes Agent configuration
+
+Add to `~/.hermes/config.yaml`:
+
+```yaml
+mcp_servers:
+  apex_device:
+    url: "http://127.0.0.1:8765/mcp"
+    headers:
+      Authorization: "Bearer <paste-token-here>"
+```
+
+Start (or restart) Hermes. Verify by asking Hermes to list devices:
+
+> Use the apex_device MCP to list connected devices.
+
+## Tools exposed
+
+All 11 device tools from `api/mcp.py`:
+
+- `take_screenshot(device_id?)`
+- `tap(x, y, device_id?)`
+- `swipe(start_x, start_y, end_x, end_y, duration_ms?, device_id?)`
+- `input_text(text, device_id?)`
+- `launch_app(app_id, device_id?)`
+- `find_text(query, device_id?)`
+- `find_icon(name, device_id?)`
+- `get_ui_tree(device_id?, include_app_info?)`
+- `describe_screen(device_id?)`
+- `list_devices()`
+- `device_status(device_id)`
+
+## Concurrency model
+
+- The cloud worker and MCP clients share the same `DeviceManager`.
+- Per-device, session-level locking: the first caller (cloud or MCP) to
+  touch a device holds it; the other side sees a busy error.
+- MCP sessions hold their lock until **20 seconds of inactivity**
+  (the `McpBusyTracker` default TTL). The mcp SDK 1.28.1 does not expose
+  a per-session shutdown callback, so a clean Hermes disconnect is also
+  recovered via the 20s TTL sweep — see the implementation note in
+  spec §6.5. Cloud assignments hold theirs until the assignment
+  terminates.
+- The cloud scheduler is told about MCP-held devices via the heartbeat
+  `mcp_busy_device_ids` field, so it normally won't even try to dispatch
+  to them. A 30-second window exists between an MCP acquire and the next
+  heartbeat; during that window cloud may dispatch, and the host-agent
+  will fail-fast the assignment with `failure_reason="device held by an
+  active MCP session"`.
+
+## Network binding
+
+The MCP endpoint is bound to the same address as the local console. By
+default this is `127.0.0.1` (loopback only). To expose on a different
+interface, set `HOST_AGENT_CONSOLE_BIND_HOST` AND
+`HOST_AGENT_CONSOLE_ALLOW_NON_LOOPBACK=true` — both are required. This
+is the same escape hatch the local console uses; there is no MCP-only
+override.
+
+## Error responses
+
+The mcp SDK 1.28.1 forces tool errors into `CallToolResult(isError=true,
+content=[TextContent(message)])` — there is no public path that surfaces
+JSON-RPC `-32000` with a structured `data.busy_owner` field from a tool
+call site. The busy-owner value lives inside the text content (full
+string for `cloud_assignment`, truncated session_id prefix for
+`mcp_session:` collisions).
+
+| Condition | JSON-RPC envelope | `result.content[0].text` |
+|---|---|---|
+| Missing/wrong bearer token | HTTP 401 (transport-level) | `{"error": "invalid token"}` + `WWW-Authenticate: Bearer` |
+| Device busy (cloud) | `result.isError = true` | `"device <X> is busy (held by cloud assignment)"` |
+| Device busy (other MCP) | `result.isError = true` | `"device <X> is busy (held by mcp_session:<8-char-prefix>)"` |
+| Unknown device | `result.isError = false` | JSON `{"ok": false, "error": "device not found: <X>"}` |
+| Tool error | `result.isError = true` | `"Error executing tool <name>: <original-message>"` |
+
+## Troubleshooting
+
+- **`list_devices` returns `[]`**: no devices registered. Use the local
+  console at `http://127.0.0.1:8765/` to add one (Login → Devices).
+- **`device X is busy` even when cloud console says device is idle**:
+  check whether another MCP session is holding it. The local console
+  dashboard shows active MCP sessions and held device_ids.
+- **Token verification fails after restart**: confirm you copied the
+  token from the current `host_mcp_token.json`, not an older one.
+  Rotation = delete file + restart.
+
+## Out of scope (current version)
+
+- `wait_until_usable` MCP tool: implemented internally but not exposed.
+  MVP callers must handle busy errors themselves.
+- MCP call history in the local console: only current state is surfaced,
+  not a call log.
+- Token rotation CLI: use delete-and-restart for now.
+- Non-loopback binding without explicit opt-in.

docs/superpowers/specs/2026-07-21-host-agent-mcp-server-design.md

@@ -38,7 +38,7 @@
 | D6 | 设备状态映射 = 走 `_device_display_status()` 同款逻辑 | 避免"所有连上的设备看起来都 busy" |
 | D7 | Cloud worker 与 MCP server 在同一 host-agent 进程并存 | 不互斥，共享 `DeviceManager` |
 | D8 | Cloud ↔ MCP 协调 = 心跳上报 `mcp_busy_device_ids`，cloud scheduler 跳过 | 心跳 schema 扩展，cloud 侧 _matches() 一处改动 |
-| D9 | MCP session 级 lazy acquire 锁，60s TTL 兜底 | session_id 来自 FastMCP 上下文 |
+| D9 | MCP session 级 lazy acquire 锁，20s TTL 兜底（mcp SDK 1.28.1 无 session-end callback，见 §6.5） | session_id 来自 FastMCP 上下文 |
 | D10 | Skill catalog 工具 MVP 不暴露，保留 `create_mcp_server(skill_catalog_store=...)` 参数化挂载点 | 未来可加 mutating 工具 |
 | D11 | `wait_until_usable` 方法实现 + 单测，但调用方不接入 | 预留能力，MVP 全部 fail-fast |
 | D12 | `tool_handlers(manager)` 改为必传 | 已 grep 确认无调用方依赖 None 默认，根治 `DeviceNotFoundError` 类静默回退地雷 |
@@ -102,7 +102,7 @@ class McpDeviceLease:
     last_seen_at: datetime
 
 class McpBusyTracker:
-    def __init__(self, *, ttl_seconds: float = 60.0, now=None) -> None: ...
+    def __init__(self, *, ttl_seconds: float = 20.0, now=None) -> None: ...
     def acquire(self, device_id: str, session_id: str) -> bool: ...
     def renew(self, device_id: str, session_id: str) -> bool: ...
     def release(self, session_id: str) -> list[str]: ...
@@ -258,32 +258,44 @@ run_async() 主循环启动（行为不变）：
 ### 6.5 Session 结束 / TTL 过期
 
 ```
-正常：Hermes 主动断开 → FastMCP 触发 session shutdown callback
+正常：Hermes 主动断开 → mcp SDK 1.28.1 没有 per-session shutdown hook
-      → mcp_busy_tracker.release(session_id) → 该 session 持有的所有 lease 释放
+      → 该 session 的 lease 进入 TTL 倒计时
-      → 下次心跳 payload 不再包含这些 device_id → cloud 重新视为 idle
+      → 20s TTL 到期 → 下次 busy_device_ids() 或 snapshot() 调用时 lazy sweep
+      → lease 清理 → 下次心跳 payload 不再包含 → cloud 重新视为 idle
 
-异常：Hermes 崩溃 / 网络断 → 无 shutdown callback
+异常：Hermes 崩溃 / 网络断 → 同上，无 shutdown callback
-      → 60s TTL 到期 → 下次 busy_device_ids() 或 snapshot() 调用时 lazy sweep
+      → 20s TTL 到期 → 下次 busy_device_ids() 或 snapshot() 调用时 lazy sweep
       → lease 清理 → 下次心跳 payload 不再包含 → cloud 重新视为 idle
 ```
 
+**Implementation note (2026-07-21 fix wave):** mcp SDK 1.28.1 exposes
+only a server-level `lifespan` hook; `ServerSession.__aexit__` and
+`StreamableHTTPSessionManager` do not surface a per-session
+shutdown callback. The spec originally described a release-on-clean-
+disconnect path that the SDK cannot deliver today. The fallback is
+the 20-second TTL sweep — short enough that a normal heartbeat
+interval (30s) catches the recovery before the cloud scheduler
+notices, long enough that an actively-busy session does not lose its
+lease during normal operator pauses. Explicit release on session end
+remains a future enhancement if/when the SDK exposes the hook.
+
 ## 7. Error Handling Matrix
 
 | # | 触发条件 | 返回语义 | 备注 |
 |---|---|---|---|
 | 1 | `Authorization` 缺失/不匹配 | HTTP 401 + `WWW-Authenticate: Bearer` + JSON `{"error":"invalid token"}` | 不写失败日志；首次成功鉴权写 INFO |
-| 2 | Cloud 占用目标设备 | JSON-RPC `-32000` + `"device X is busy (held by cloud assignment)"` + `data.busy_owner = "cloud_assignment"` | DEBUG 日志 |
+| 2 | Cloud 占用目标设备 | `CallToolResult(isError=true, content=[TextContent("device phone-1 is busy (held by cloud assignment)")])` | DEBUG 日志 |
-| 3 | 另一 MCP session 占用 | JSON-RPC `-32000` + `"device X is busy (held by another MCP session)"` + `data.busy_owner = "mcp_session:<prefix>"` | DEBUG 日志 |
+| 3 | 另一 MCP session 占用 | `CallToolResult(isError=true, content=[TextContent("device phone-1 is busy (held by mcp_session:<8-char-prefix>)")])` | DEBUG 日志 |
-| 4 | `device_id` 不存在 | JSON-RPC `-32602` + `"unknown device: X"` | 复用 `call_with_semantic_errors` |
+| 4 | `device_id` 不存在 | `CallToolResult(isError=false)` + JSON `{"ok": false, "error": "device not found: phone-1"}` | 复用 `call_with_semantic_errors`；语义错误不抛 |
-| 5 | 工具底层异常 | JSON-RPC `-32000` + 原异常 message | WARNING + exc_info |
+| 5 | 工具底层异常 | `CallToolResult(isError=true, content=[TextContent("Error executing tool <name>: <orig-msg>")])` | WARNING + exc_info |
 | 6 | Cloud assignment 启动前命中 MCP 占用 | `AssignmentExecutionResult(status="failed", failure_reason="device held by active MCP session")` | INFO 一次 |
 | 7 | Token 文件损坏 JSON | host-agent 启动失败，stderr 提示 | 不静默重新生成 |
 | 8 | Token 文件不可写 | host-agent 启动失败 | 同上 |
-| 9 | MCP session 异常断开 | lease 进入 TTL 倒计时 | 60s 后 lazy sweep |
+| 9 | MCP session 异常断开 | lease 进入 TTL 倒计时 | 20s 后 lazy sweep |
 | 10 | TTL 过期瞬间 Hermes 重连 | renew 容忍边界：session_id 匹配 → 重新 acquire 而非报错 | 无感 |
 | 11 | 同 session 并发不同设备 | 各自独立 acquire | per-device 设计 |
 | 12 | 同 session 并发同一设备 | 第一个 acquire；第二个 renew（同 session_id） | 并发 safe |
-| 13 | FastMCP 提取不到 session_id | JSON-RPC `-32001` + `"cannot determine MCP session"` | ERROR + exc_info |
+| 13 | FastMCP 提取不到 session_id | `CallToolResult(isError=true, content=[TextContent("cannot determine MCP session")])` | ERROR + exc_info |
 | 14 | host-agent 关停时有 active MCP session | lease 随进程退出消失 | 不需显式清理 |
 
 ### 错误返回格式
@@ -292,17 +304,32 @@ run_async() 主循环启动（行为不变）：
 {
   "jsonrpc": "2.0",
   "id": "<request-id>",
-  "error": {
+  "result": {
-    "code": -32000,
+    "content": [
-    "message": "device phone-1 is busy (held by cloud assignment)",
+      {
-    "data": {
+        "type": "text",
-      "device_id": "phone-1",
+        "text": "device phone-1 is busy (held by cloud assignment)"
-      "busy_owner": "cloud_assignment"
+      }
-    }
+    ],
+    "isError": true
   }
 }
 ```
 
+**Implementation note (2026-07-21 fix wave):** mcp SDK 1.28.1's
+`Tool.run` wraps every non-`UrlElicitationRequiredError` exception
+(including `McpError` with a typed `ErrorData`) into `ToolError`.
+The lowlevel `call_tool` handler then serializes any exception as
+`CallToolResult(isError=true, content=[TextContent(message)])` via
+`_make_error_result`. There is no public path that surfaces JSON-RPC
+`-32000` with a structured `data.busy_owner` field from a tool call
+site — the SDK's wire contract for tool errors is the `isError=true`
+flag plus text content. The busy-owner value lives in the text
+content (truncated session_id for `mcp_session:` collisions, full
+string for `cloud_assignment`). Unknown-device and other semantic
+errors are returned as normal `ok=False` payloads inside a successful
+`CallToolResult(isError=false)` (see `api/mcp.py::call_with_semantic_errors`).
+
 ## 8. Testing Strategy
 
 ### 8.1 单元测试
@@ -376,13 +403,13 @@ run_async() 主循环启动（行为不变）：
 - **Q2**：`mcp-token` CLI 是否需要鉴权？→ MVP 不鉴权，假定能访问宿主机的操作者可信（与 `setup` 子命令同款）。后续可加 `--password` 校验 local_account。
 - **Q3**：MCP 工具调用是否需要 wall-clock 超时？→ MVP 不加，依赖底层超时；如有"Hermes 调用挂死"报告再加。
 - **Q4**：心跳扩展是 Alembic migration 还是仅 schema 字段？→ MVP 仅 transient 字段（heartbeat 接收 → scheduler 用 → 丢弃），无需 migration。
-- **Q5（待实测）**：60s TTL 是否合适？→ 实测后调整。太短容易误释放正常 session 的锁；太长 Hermes 崩溃后设备不可用窗口大。
+- **Q5（已答，2026-07-21 fix wave）**：TTL 从 60s 降到 20s，因为 mcp SDK 1.28.1 没有 per-session shutdown callback（见 §6.5）。20s 仍能容许正常 operator 暂停，但能在一次 30s 心跳窗口内回收崩盘 session 的锁；新 `test_default_ttl_is_20_seconds` 和 `test_default_ttl_recovers_dead_session_within_one_window` 锁定该值。如有"Hermes 长操作横跨 20s 静默"报告再调高。
 
 ## 11. Risks
 
 - **R1**：Cloud 心跳窗口期（30s）冲突。缓解：AssignmentExecutor 启动前 fail-fast。残留：cloud 可能基于过期心跳派任务、host-agent fail、cloud 重试——浪费 attempt 配额。**接受**。
 - **R2**：Hermes 长时间占用设备导致 cloud 任务反复 fail。MVP 无自动缓解；用户手动管控；未来启用 `wait_until_usable`。**接受**。
-- **R3**：Hermes 崩溃后 60s 内设备不可用。TTL 兜底但窗口存在。**接受，记入 Q5**。
+- **R3**：Hermes 崩溃后 ≤20s 设备不可用（TTL 兜底，但窗口存在）。窗口仍 ≤30s 心跳间隔，cloud 侧下次心跳能学到。**接受，记入 Q5**。
 - **R4（已消除）**：`tool_handlers` 签名改动影响面。Grep 确认 0 调用方依赖 None 默认。
 - **R5**：FastMCP `session_id` 提取依赖 `mcp` SDK 内部 API。缓解：e2e 测试覆盖；SDK 升级 CI 能及时暴露。
 - **R6**：`mcp` SDK 需作为 device-host-agent 直接依赖（目前通过 Runtime 传递）。需加进 `apps/device-host-agent/pyproject.toml`（与 `filelock` 直接化先例一致）。

packages/cloud-platform/cloud/db_models.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 from sqlalchemy import (
+    Boolean,
     ForeignKey,
     Index,
     Integer,
@@ -86,6 +87,7 @@ class PooledDeviceRow(Base):
     status: Mapped[str] = mapped_column(String, nullable=False)
     capability_tags_json: Mapped[str] = mapped_column(Text, nullable=False)
     synced_at: Mapped[str | None] = mapped_column(String, nullable=True)
+    mcp_busy: Mapped[bool] = mapped_column(Boolean, nullable=False, default=False)
 
 
 class ScheduledTaskRow(Base):

packages/cloud-platform/cloud/internal_api/api.py

@@ -185,6 +185,7 @@ def create_internal_router(
             address=payload.address,
             allow_device_takeover=allow_device_takeover,
             planner_transport=payload.planner_transport,
+            mcp_busy_device_ids=payload.mcp_busy_device_ids,
         )
         policy = pool.store.get_host_governance_policy(host_id)
         policy_revision = policy.revision if policy is not None else 0

packages/cloud-platform/cloud/internal_api/models.py

@@ -40,6 +40,7 @@ class HeartbeatRequest(BaseModel):
     devices: list[DeviceSnapshotModel] = Field(default_factory=list)
     policy_revision: int = Field(default=0, ge=0)
     planner_transport: Literal["direct", "cloud"] = "direct"
+    mcp_busy_device_ids: list[str] = Field(default_factory=list)
 
 
 class HostGovernancePolicyModel(BaseModel):

packages/cloud-platform/cloud/migrations/versions/0014_pooled_device_mcp_busy.py

@@ -0,0 +1,28 @@
+"""Add mcp_busy flag column to pooled_devices."""
+
+from __future__ import annotations
+
+import sqlalchemy as sa
+from alembic import op
+
+
+revision = "0014_pooled_device_mcp_busy"
+down_revision = "0013_task_cancellation"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "pooled_devices",
+        sa.Column(
+            "mcp_busy",
+            sa.Boolean(),
+            nullable=False,
+            server_default=sa.false(),
+        ),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("pooled_devices", "mcp_busy")

packages/cloud-platform/cloud/pool.py

@@ -47,6 +47,7 @@ class PooledDevice:
     status: PooledDeviceStatus
     capability_tags: list[str] = field(default_factory=list)
     synced_at: datetime | None = None
+    mcp_busy: bool = False
 
 
 class DevicePool:
@@ -64,6 +65,7 @@ class DevicePool:
         address: str | None = None,
         planner_transport: Literal["direct", "cloud"] = "direct",
         allow_device_takeover: bool = False,
+        mcp_busy_device_ids: list[str] | None = None,
     ) -> None:
         """Push a host's current device snapshot into the pool.
 
@@ -78,7 +80,11 @@ class DevicePool:
             last_seen_at=now,
             planner_transport=planner_transport,
         )
-        devices = [self._to_pooled(device, host_id, now) for device in snapshot]
+        busy_set = set(mcp_busy_device_ids or [])
+        devices = [
+            self._to_pooled(device, host_id, now, mcp_busy=device.id in busy_set)
+            for device in snapshot
+        ]
         if allow_device_takeover:
             self.store.replace_host_devices(
                 host_id,
@@ -119,6 +125,8 @@ class DevicePool:
         device: Device,
         host_id: str,
         synced_at: datetime,
+        *,
+        mcp_busy: bool = False,
     ) -> PooledDevice:
         raw_status = (
             device.status if device.status in _HOST_REPORTED_STATUSES else "idle"
@@ -131,6 +139,7 @@ class DevicePool:
             status=raw_status,  # type: ignore[arg-type]
             capability_tags=tags,
             synced_at=synced_at,
+            mcp_busy=mcp_busy,
         )
 
     def _is_stale(self, host: HostRegistration, now: datetime) -> bool:

packages/cloud-platform/cloud/scheduler.py

@@ -204,6 +204,8 @@ class TaskScheduler:
 
 
 def _matches(device: "PooledDevice", constraints: TaskConstraints) -> bool:
+    if device.mcp_busy:
+        return False
     if constraints.target_host_id and device.host_id != constraints.target_host_id:
         return False
     if (

packages/cloud-platform/cloud/schema.py

@@ -9,7 +9,7 @@ from alembic.runtime.migration import MigrationContext
 from cloud.database import create_database_engine, normalize_database_url
 
 
-HEAD_REVISION = "0013_task_cancellation"
+HEAD_REVISION = "0014_pooled_device_mcp_busy"
 
 
 class SchemaVersionError(RuntimeError):

packages/cloud-platform/cloud/sql_repository.py

@@ -342,6 +342,7 @@ class SQLAlchemyCloudRepository:
                             ensure_ascii=False,
                         ),
                         synced_at=_iso(device.synced_at) if device.synced_at else None,
+                        mcp_busy=getattr(device, "mcp_busy", False),
                     )
                     for device in devices
                 ]
@@ -2232,6 +2233,7 @@ def _device_from_row(row: PooledDeviceRow) -> Any:
         status=row.status,
         capability_tags=tags,
         synced_at=_parse_dt(row.synced_at),
+        mcp_busy=bool(getattr(row, "mcp_busy", False)),
     )
 
 

packages/cloud-platform/tests/test_internal_api_models.py

@@ -0,0 +1,20 @@
+from __future__ import annotations
+
+from cloud.internal_api.models import HeartbeatRequest
+
+
+def test_heartbeat_request_defaults_mcp_busy_device_ids_to_empty() -> None:
+    req = HeartbeatRequest(host_id="h1")
+    assert req.mcp_busy_device_ids == []
+
+
+def test_heartbeat_request_accepts_mcp_busy_device_ids() -> None:
+    req = HeartbeatRequest(host_id="h1", mcp_busy_device_ids=["phone-1"])
+    assert req.mcp_busy_device_ids == ["phone-1"]
+
+
+def test_heartbeat_request_omitting_field_is_backward_compatible() -> None:
+    """Old host-agents that don't send the field must still validate."""
+    raw = {"host_id": "h1", "devices": []}
+    req = HeartbeatRequest.model_validate(raw)
+    assert req.mcp_busy_device_ids == []

packages/cloud-platform/tests/test_pool.py

@@ -0,0 +1,68 @@
+"""Tests for the cloud DevicePool, focused on the mcp_busy flag plumbing."""
+
+from __future__ import annotations
+
+import tempfile
+from pathlib import Path
+
+import pytest
+
+from cloud.config import CloudConfig
+from cloud.pool import DevicePool
+from cloud.store import CloudStore
+from core.models import Device
+
+
+@pytest.fixture
+def pool() -> DevicePool:
+    """Build a fresh DevicePool backed by a temporary SQLite file."""
+    with tempfile.TemporaryDirectory() as tmp:
+        store = CloudStore(Path(tmp) / "cloud.sqlite3")
+        try:
+            yield DevicePool(store=store, config=CloudConfig())
+        finally:
+            store.close()
+
+
+def _device(device_id: str, *, status: str = "idle") -> Device:
+    return Device(
+        id=device_id,
+        driver_type="wda",
+        status=status,  # type: ignore[arg-type]
+        capability_tags=[],
+    )
+
+
+def test_sync_host_devices_marks_mcp_busy_devices(pool: DevicePool) -> None:
+    """When a host reports device-1 as MCP-busy, the pool PooledDevice for
+    device-1 has mcp_busy=True."""
+    pool.sync_host_devices(
+        "host-1",
+        [_device("device-1", status="idle")],
+        mcp_busy_device_ids=["device-1"],
+    )
+    devices = pool.list_devices()
+    busy = [d for d in devices if d.device_id == "device-1"]
+    assert len(busy) == 1
+    assert busy[0].mcp_busy is True
+
+
+def test_sync_host_devices_default_mcp_busy_is_false(pool: DevicePool) -> None:
+    pool.sync_host_devices("host-1", [_device("device-1", status="idle")])
+    devices = pool.list_devices()
+    assert devices[0].mcp_busy is False
+
+
+def test_sync_host_devices_clears_mcp_busy_on_next_sync(
+    pool: DevicePool,
+) -> None:
+    """MCP releases device -> next heartbeat without device in
+    mcp_busy_device_ids -> pool reflects mcp_busy=False."""
+    pool.sync_host_devices(
+        "host-1",
+        [_device("device-1", status="idle")],
+        mcp_busy_device_ids=["device-1"],
+    )
+    pool.sync_host_devices("host-1", [_device("device-1", status="idle")])
+    devices = pool.list_devices()
+    assert devices[0].mcp_busy is False

packages/cloud-platform/tests/test_scheduler.py

@@ -0,0 +1,53 @@
+"""Tests for the cloud TaskScheduler, focused on skipping MCP-busy devices."""
+
+from __future__ import annotations
+
+import tempfile
+from pathlib import Path
+
+import pytest
+
+from cloud.config import CloudConfig
+from cloud.pool import DevicePool
+from cloud.scheduler import TaskConstraints, TaskScheduler
+from cloud.store import CloudStore
+from core.models import Device
+
+
+@pytest.fixture
+def pool() -> DevicePool:
+    with tempfile.TemporaryDirectory() as tmp:
+        store = CloudStore(Path(tmp) / "cloud.sqlite3")
+        try:
+            yield DevicePool(store=store, config=CloudConfig())
+        finally:
+            store.close()
+
+
+def _device(device_id: str, *, status: str = "idle") -> Device:
+    return Device(
+        id=device_id,
+        driver_type="wda",
+        status=status,  # type: ignore[arg-type]
+        capability_tags=[],
+    )
+
+
+def test_mcp_busy_device_is_skipped_by_scheduler(pool: DevicePool) -> None:
+    """A device with mcp_busy=True is not selected for assignment.
+
+    Two devices exist: dev-busy (idle status, mcp_busy=True) and dev-idle
+    (idle status, mcp_busy=False). One task is submitted with no
+    constraints, so both are candidates before the mcp_busy filter.
+    The scheduler must pick dev-idle.
+    """
+    pool.sync_host_devices(
+        "host-1",
+        [_device("dev-busy"), _device("dev-idle")],
+        mcp_busy_device_ids=["dev-busy"],
+    )
+    scheduler = TaskScheduler(pool=pool, store=pool.store, config=CloudConfig())
+    scheduler.submit(goal="test", constraints=TaskConstraints())
+    assignments = scheduler.assign()
+    assert len(assignments) == 1
+    assert assignments[0].device_id == "dev-idle"

tests/test_mcp.py

@@ -64,3 +64,12 @@ def test_mcp_ui_tree_can_include_active_app_info() -> None:
         "activity": ".MainActivity",
     }
     assert isinstance(response["nodes"], list)
+
+
+def test_tool_handlers_requires_manager() -> None:
+    """D12: tool_handlers must not silently fall back to DEFAULT_MANAGER."""
+    from api.mcp import tool_handlers
+    import pytest
+
+    with pytest.raises(TypeError):
+        tool_handlers()  # type: ignore[call-arg]

tests/test_skill_catalog_mcp.py

@@ -316,8 +316,10 @@ def test_create_mcp_server_registers_skill_tools_when_store_provided(seeded_stor
     """Wire-up: api.mcp.create_mcp_server must register skill tools when
     skill_catalog_store is provided."""
     from api.mcp import create_mcp_server
+    from device.manager import DeviceManager
 
     server = create_mcp_server(
+        manager=DeviceManager(),
         skill_catalog_store=seeded_store,
         skill_active_subscriptions={"sub-a"},
     )
@@ -329,8 +331,9 @@ def test_create_mcp_server_registers_skill_tools_when_store_provided(seeded_stor
 def test_create_mcp_server_omits_skill_tools_when_no_store():
     """Wire-up must not break existing behavior when no store is provided."""
     from api.mcp import create_mcp_server
+    from device.manager import DeviceManager
 
-    server = create_mcp_server()
+    server = create_mcp_server(manager=DeviceManager())
     names = _fastmcp_tool_names(server)
     assert "list_skills" not in names
     assert "tap" in names  # existing device tools present

uv.lock

@@ -480,6 +480,7 @@ dependencies = [
     { name = "filelock" },
     { name = "httpx" },
     { name = "jinja2" },
+    { name = "mcp" },
     { name = "uvicorn", extra = ["standard"] },
 ]
 
@@ -491,6 +492,7 @@ requires-dist = [
     { name = "filelock", specifier = ">=3.0" },
     { name = "httpx", specifier = ">=0.27.0" },
     { name = "jinja2", specifier = ">=3.1" },
+    { name = "mcp", specifier = ">=1.28,<2" },
     { name = "uvicorn", extras = ["standard"], specifier = ">=0.30.0" },
 ]