diff --git a/packages/cloud-platform/cloud/db_models.py b/packages/cloud-platform/cloud/db_models.py
index a33c099..e6acbe2 100644
--- a/packages/cloud-platform/cloud/db_models.py
+++ b/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):
diff --git a/packages/cloud-platform/cloud/internal_api/api.py b/packages/cloud-platform/cloud/internal_api/api.py
index 057bafa..fb19fdf 100644
--- a/packages/cloud-platform/cloud/internal_api/api.py
+++ b/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
diff --git a/packages/cloud-platform/cloud/migrations/versions/0014_pooled_device_mcp_busy.py b/packages/cloud-platform/cloud/migrations/versions/0014_pooled_device_mcp_busy.py
new file mode 100644
index 0000000..e8bd338
--- /dev/null
+++ b/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")
\ No newline at end of file
diff --git a/packages/cloud-platform/cloud/pool.py b/packages/cloud-platform/cloud/pool.py
index dfac7c4..ce09e63 100644
--- a/packages/cloud-platform/cloud/pool.py
+++ b/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 +80,13 @@ 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 +127,8 @@ 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 +141,7 @@ 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:
diff --git a/packages/cloud-platform/cloud/scheduler.py b/packages/cloud-platform/cloud/scheduler.py
index 2a5a293..83c3626 100644
--- a/packages/cloud-platform/cloud/scheduler.py
+++ b/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 (
diff --git a/packages/cloud-platform/cloud/sql_repository.py b/packages/cloud-platform/cloud/sql_repository.py
index 402d876..9ad8ab0 100644
--- a/packages/cloud-platform/cloud/sql_repository.py
+++ b/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)),
     )
 
 
diff --git a/packages/cloud-platform/tests/test_pool.py b/packages/cloud-platform/tests/test_pool.py
new file mode 100644
index 0000000..cf85a53
--- /dev/null
+++ b/packages/cloud-platform/tests/test_pool.py
@@ -0,0 +1,72 @@
+"""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
\ No newline at end of file
diff --git a/packages/cloud-platform/tests/test_scheduler.py b/packages/cloud-platform/tests/test_scheduler.py
new file mode 100644
index 0000000..c2425a9
--- /dev/null
+++ b/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"
\ No newline at end of file