feat(host-agent): stop assignment execution collaboratively on cancellation

- LeaseGuard gains an is_cancellation convenience property
- ActiveAssignmentRunner marks the lease lost with a cancellation
  reason when a renewal response reports cancel_requested
- AssignmentExecutor threads stop_reason through to TaskRunner/
  WorkflowRunner and maps a cancellation-flavored stop to
  AssignmentExecutionResult.status = "cancelled" instead of "failed"
- AssignmentProcessor forwards a three-way done/cancelled/failed
  status when reporting the terminal result
- Add/extend tests across lease, assignment, processor, and client

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

@@ -9,6 +9,7 @@ from core.models import Task
 from host_agent.execution import ExecutionFactories
 from host_agent.planner_context import bind_planner_execution_context
 from host_agent.progress import TaskProgressHolder, TaskProgressSnapshot
+from runtime.task import is_cancellation_reason
 
 
 @dataclass(frozen=True)
@@ -32,18 +33,24 @@ class AssignmentExecutor:
         assignment: AssignmentModel,
         *,
         should_stop: Callable[[], bool] | None = None,
+        stop_reason: Callable[[], str | None] | None = None,
     ) -> AssignmentExecutionResult:
         self._progress.clear()
         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
                 return AssignmentExecutionResult(
-                    status="failed",
-                    failure_reason="execution interrupted",
+                    status="cancelled" if is_cancellation_reason(reason) else "failed",
+                    failure_reason=reason or "execution interrupted",
                 )
             if assignment.workflow_definition_id is not None:
-                return self._execute_workflow(assignment, should_stop=should_stop)
+                return self._execute_workflow(
+                    assignment, should_stop=should_stop, stop_reason=stop_reason
+                )
             if assignment.goal is not None:
-                return self._execute_goal(assignment, should_stop=should_stop)
+                return self._execute_goal(
+                    assignment, should_stop=should_stop, stop_reason=stop_reason
+                )
             return AssignmentExecutionResult(
                 status="failed",
                 failure_reason="assignment has neither goal nor workflow definition",
@@ -54,6 +61,7 @@ class AssignmentExecutor:
         assignment: AssignmentModel,
         *,
         should_stop: Callable[[], bool] | None,
+        stop_reason: Callable[[], str | None] | None,
     ) -> AssignmentExecutionResult:
         task = Task(goal=assignment.goal or "", device_id=assignment.device_id)
         if self.factories.metadata_store is not None:
@@ -67,9 +75,11 @@ class AssignmentExecutor:
         if should_stop is None:
             completed = runner.run(task)
         else:
-            completed = runner.run(task, should_stop=should_stop)
+            completed = runner.run(
+                task, should_stop=should_stop, stop_reason=stop_reason
+            )
         return AssignmentExecutionResult(
-            status="done" if completed.status == "completed" else "failed",
+            status=_terminal_status(completed.status),
             failure_reason=completed.failure_reason,
             metadata={
                 "runtime_task_id": completed.id,
@@ -82,6 +92,7 @@ class AssignmentExecutor:
         assignment: AssignmentModel,
         *,
         should_stop: Callable[[], bool] | None,
+        stop_reason: Callable[[], str | None] | None,
     ) -> AssignmentExecutionResult:
         definition_id = assignment.workflow_definition_id or ""
         definition = self.factories.workflow_store.get_definition(definition_id)
@@ -98,9 +109,10 @@ class AssignmentExecutor:
                 definition,
                 device_id=assignment.device_id,
                 should_stop=should_stop,
+                stop_reason=stop_reason,
             )
         return AssignmentExecutionResult(
-            status="done" if run.status == "completed" else "failed",
+            status=_terminal_status(run.status),
             failure_reason=(
                 None if run.status == "completed" else f"workflow ended as {run.status}"
             ),
@@ -109,3 +121,11 @@ class AssignmentExecutor:
                 "workflow_status": run.status,
             },
         )
+
+
+def _terminal_status(runtime_status: str) -> str:
+    if runtime_status == "completed":
+        return "done"
+    if runtime_status == "cancelled":
+        return "cancelled"
+    return "failed"

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

@@ -12,6 +12,7 @@ from cloud.internal_api.models import AssignmentModel
 from host_agent.assignment import AssignmentExecutionResult
 from host_agent.client import HostAgentAPIError, HostAgentClient, StaleLeaseError
 from host_agent.progress import TaskProgressSnapshot
+from runtime.task import is_cancellation_reason
 
 
 class InterruptibleAssignmentExecutor(Protocol):
@@ -20,6 +21,7 @@ class InterruptibleAssignmentExecutor(Protocol):
         assignment: AssignmentModel,
         *,
         should_stop: Callable[[], bool] | None = None,
+        stop_reason: Callable[[], str | None] | None = None,
     ) -> AssignmentExecutionResult: ...
 
     def latest_progress(self) -> TaskProgressSnapshot | None: ...
@@ -36,6 +38,10 @@ class LeaseGuard:
         with self._lock:
             return self._reason
 
+    @property
+    def is_cancellation(self) -> bool:
+        return is_cancellation_reason(self.reason)
+
     def is_lost(self) -> bool:
         return self._lost.is_set()
 
@@ -69,6 +75,7 @@ class ActiveAssignmentRunner:
                 self.executor.execute,
                 assignment,
                 should_stop=lambda: guard.is_lost() or self._stop_requested.is_set(),
+                stop_reason=lambda: guard.reason,
             )
         )
         renewal = asyncio.create_task(
@@ -108,4 +115,7 @@ class ActiveAssignmentRunner:
                 guard.mark_lost("lease renewal failed after transport retries")
                 return
             else:
+                if response.cancel_requested:
+                    guard.mark_lost("cancellation requested by control plane")
+                    return
                 lease_expires_at = response.lease_expires_at

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

@@ -47,8 +47,11 @@ class AssignmentProcessor:
             self.status_tracker.mark_assignment_started(assignment)
         try:
             execution = await self.active_executor.run(assignment)
-            status = "done" if execution.status == "done" else "failed"
-            failure_reason = execution.failure_reason if status == "failed" else None
+            if execution.status in {"done", "cancelled"}:
+                status = execution.status
+            else:
+                status = "failed"
+            failure_reason = execution.failure_reason if status != "done" else None
             response = await self.client.report_result(
                 assignment,
                 status=status,

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

@@ -78,6 +78,39 @@ def test_goal_assignment_preserves_runtime_failure_reason() -> None:
     assert result.failure_reason == "planner unavailable"
 
 
+def test_goal_assignment_maps_cancellation_stop_to_cancelled_status() -> None:
+    # First should_stop() call is Executor.execute()'s pre-flight check (must pass
+    # through so the runner is actually invoked); the runner's own loop then stops.
+    calls = {"count": 0}
+
+    def should_stop() -> bool:
+        calls["count"] += 1
+        return calls["count"] > 1
+
+    class FakeTaskRunner:
+        def run(self, task: Task, *, should_stop=None, stop_reason=None) -> Task:
+            assert should_stop is not None and should_stop()
+            assert stop_reason is not None
+            task.status = "cancelled"
+            task.failure_reason = stop_reason()
+            return task
+
+    factories = 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]
+    )
+
+    result = AssignmentExecutor(factories).execute(
+        _assignment(),
+        should_stop=should_stop,
+        stop_reason=lambda: "cancellation requested by control plane",
+    )
+
+    assert result.status == "cancelled"
+    assert result.failure_reason == "cancellation requested by control plane"
+
+
 def test_workflow_assignment_loads_and_executes_definition() -> None:
     definition = object()
     calls: list[tuple[object, str]] = []
@@ -109,6 +142,44 @@ def test_workflow_assignment_loads_and_executes_definition() -> None:
     }
 
 
+def test_workflow_assignment_maps_cancellation_stop_to_cancelled_status() -> None:
+    calls = {"count": 0}
+
+    def should_stop() -> bool:
+        calls["count"] += 1
+        return calls["count"] > 1
+
+    class FakeWorkflowStore:
+        def get_definition(self, definition_id: str):
+            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):
+            assert should_stop is not None and should_stop()
+            assert stop_reason is not None
+            return SimpleNamespace(
+                id="run-a", status="cancelled", failure_reason=stop_reason()
+            )
+
+    factories = ExecutionFactories(
+        task_runner_factory=lambda: object(),  # type: ignore[arg-type,return-value]
+        workflow_runner_factory=lambda: FakeWorkflowRunner(),  # type: ignore[arg-type,return-value]
+        workflow_store=FakeWorkflowStore(),  # type: ignore[arg-type]
+    )
+
+    result = AssignmentExecutor(factories).execute(
+        _assignment(goal=None, workflow_definition_id="workflow-a"),
+        should_stop=should_stop,
+        stop_reason=lambda: "cancellation requested by control plane",
+    )
+
+    assert result.status == "cancelled"
+    assert result.metadata == {
+        "workflow_run_id": "run-a",
+        "workflow_status": "cancelled",
+    }
+
+
 def test_unknown_workflow_fails_without_running() -> None:
     class FakeWorkflowStore:
         def get_definition(self, definition_id: str):

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

@@ -140,6 +140,30 @@ def test_stale_lease_response_raises_typed_error_without_retry() -> None:
     assert attempts == 1
 
 
+def test_renew_deserializes_cancel_requested_flag() -> None:
+    def handler(request: httpx.Request) -> httpx.Response:
+        return httpx.Response(
+            200,
+            json={
+                "status": "renewed",
+                "lease_expires_at": "2026-07-12T00:05:00Z",
+                "cancel_requested": True,
+            },
+        )
+
+    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)
+            response = await client.renew(_assignment())
+            assert response.status == "renewed"
+            assert response.cancel_requested is True
+
+    asyncio.run(scenario())
+
+
 def test_result_report_retries_identical_payload_after_response_loss() -> None:
     payloads: list[dict[str, object]] = []
 

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

@@ -29,7 +29,7 @@ def test_lease_renews_while_execution_is_active() -> None:
         renewed = asyncio.Event()
 
         class BlockingExecutor:
-            def execute(self, assignment, *, should_stop=None):
+            def execute(self, assignment, *, should_stop=None, stop_reason=None):
                 execution_started.set()
                 release_execution.wait(timeout=2)
                 return AssignmentExecutionResult(status="done")
@@ -61,13 +61,13 @@ def test_lease_renews_while_execution_is_active() -> None:
     asyncio.run(scenario())
 
 
-def test_stale_lease_stops_later_interruptible_actions() -> None:
+def test_cancel_requested_renewal_stops_execution_with_cancelled_status() -> None:
     async def scenario() -> None:
         first_action_started = Event()
         actions: list[str] = []
 
         class CooperativeExecutor:
-            def execute(self, assignment, *, should_stop=None):
+            def execute(self, assignment, *, should_stop=None, stop_reason=None):
                 assert should_stop is not None
                 actions.append("first")
                 first_action_started.set()
@@ -76,9 +76,59 @@ def test_stale_lease_stops_later_interruptible_actions() -> None:
                     Event().wait(0.001)
                 if not should_stop():
                     actions.append("second")
+                reason = stop_reason() if stop_reason is not None else None
                 return AssignmentExecutionResult(
-                    status="failed",
-                    failure_reason="execution interrupted",
+                    status="cancelled" if reason and "cancel" in reason else "failed",
+                    failure_reason=reason,
+                )
+
+            def latest_progress(self):
+                return None
+
+        class CancellingClient:
+            async def renew(self, assignment, *, progress=None):
+                assert await asyncio.to_thread(first_action_started.wait, 1)
+                return LeaseRenewalResponse(
+                    status="renewed",
+                    lease_expires_at=datetime.now(UTC) + timedelta(seconds=30),
+                    cancel_requested=True,
+                )
+
+        result = await asyncio.wait_for(
+            ActiveAssignmentRunner(
+                CancellingClient(),  # type: ignore[arg-type]
+                CooperativeExecutor(),
+            ).run(_assignment()),
+            timeout=1,
+        )
+
+        assert result.status == "cancelled"
+        assert result.failure_reason == "cancellation requested by control plane"
+        assert actions == ["first"]
+
+    asyncio.run(scenario())
+
+
+def test_stale_lease_stops_later_interruptible_actions() -> None:
+    async def scenario() -> None:
+        first_action_started = Event()
+        actions: list[str] = []
+
+        class CooperativeExecutor:
+            def execute(self, assignment, *, should_stop=None, stop_reason=None):
+                assert should_stop is not None
+                actions.append("first")
+                first_action_started.set()
+                assert first_action_started.wait(timeout=1)
+                while not should_stop():
+                    Event().wait(0.001)
+                if not should_stop():
+                    actions.append("second")
+                reason = stop_reason() if stop_reason is not None else None
+                assert reason == "lease rejected by control plane"
+                return AssignmentExecutionResult(
+                    status="cancelled" if reason and "cancel" in reason else "failed",
+                    failure_reason=reason,
                 )
 
             def latest_progress(self):
@@ -108,7 +158,7 @@ def test_renewal_loop_exits_when_execution_finishes() -> None:
         renew_calls = 0
 
         class ImmediateExecutor:
-            def execute(self, assignment, *, should_stop=None):
+            def execute(self, assignment, *, should_stop=None, stop_reason=None):
                 return AssignmentExecutionResult(status="done")
 
             def latest_progress(self):
@@ -142,7 +192,7 @@ def test_shutdown_request_stops_active_execution_cooperatively() -> None:
         execution_started = Event()
 
         class CooperativeExecutor:
-            def execute(self, assignment, *, should_stop=None):
+            def execute(self, assignment, *, should_stop=None, stop_reason=None):
                 assert should_stop is not None
                 execution_started.set()
                 while not should_stop():

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

@@ -88,6 +88,38 @@ def test_processor_preserves_runtime_failure_reason() -> None:
     asyncio.run(scenario())
 
 
+def test_processor_reports_cancelled_status_with_reason() -> None:
+    async def scenario() -> None:
+        reports: list[dict[str, object]] = []
+
+        class CancelledExecutor:
+            async def run(self, assignment):
+                return AssignmentExecutionResult(
+                    status="cancelled",
+                    failure_reason="cancellation requested by control plane",
+                    metadata={"runtime_status": "cancelled"},
+                )
+
+        class RecordingClient:
+            async def report_result(self, assignment, **kwargs):
+                reports.append(kwargs)
+                return TerminalResultResponse(status="recorded")
+
+        result = await AssignmentProcessor(
+            RecordingClient(),  # type: ignore[arg-type]
+            CancelledExecutor(),
+        ).process(_assignment())
+
+        assert result.report_status == "recorded"
+        assert reports[0] == {
+            "status": "cancelled",
+            "failure_reason": "cancellation requested by control plane",
+            "result": {"runtime_status": "cancelled"},
+        }
+
+    asyncio.run(scenario())
+
+
 def test_status_tracker_sees_started_then_finished_even_on_raise() -> None:
     async def scenario() -> None:
         tracker = AgentStatusTracker()

openspec/changes/task-cancellation/tasks.md

@@ -29,12 +29,12 @@
 
 ## 4. Host Agent collaborative stop
 
-- [ ] 4.1 Extend `LeaseGuard` (`host_agent/lease.py`) with a `reason` attribute already implied by `mark_lost(reason)` — confirm it's readable, add a `is_cancellation` helper or convention (e.g. reason string prefix) to distinguish cancellation from other lost-lease reasons.
-- [ ] 4.2 Update `ActiveAssignmentRunner._renew_while_running()` (`host_agent/lease.py`): when `response.cancel_requested` is true, call `guard.mark_lost("cancellation requested by control plane")` instead of continuing the renewal loop.
-- [ ] 4.3 Update `client.py`'s `renew()` to ensure `LeaseRenewalResponse.cancel_requested` deserializes correctly (should be automatic via Pydantic model update, but add a test).
-- [ ] 4.4 Update `AssignmentExecutor._execute_goal()` and `_execute_workflow()` (`host_agent/assignment.py`) to map a cancellation-flavored stop to `AssignmentExecutionResult.status = "cancelled"` (new value alongside `"done"`/`"failed"`), reading the underlying `Task`/`WorkflowRun` status (`"cancelled"`) instead of collapsing it to `"failed"`.
-- [ ] 4.5 Update `AssignmentProcessor.process()` (`host_agent/processor.py`) so its `status = "done" if execution.status == "done" else "failed"` mapping becomes a three-way mapping that preserves `"cancelled"`, and `report_result` is called with `status="cancelled"` in that case.
-- [ ] 4.6 Add/extend Host Agent tests covering: a renewal response with `cancel_requested=True` stops the active `should_stop`-driven loop; the resulting `AssignmentExecutionResult.status` and reported terminal status are `"cancelled"`; a lease-loss stop unrelated to cancellation still reports `"failed"`.
+- [x] 4.1 Extend `LeaseGuard` (`host_agent/lease.py`) with a `reason` attribute already implied by `mark_lost(reason)` — confirm it's readable, add a `is_cancellation` helper or convention (e.g. reason string prefix) to distinguish cancellation from other lost-lease reasons.
+- [x] 4.2 Update `ActiveAssignmentRunner._renew_while_running()` (`host_agent/lease.py`): when `response.cancel_requested` is true, call `guard.mark_lost("cancellation requested by control plane")` instead of continuing the renewal loop.
+- [x] 4.3 Update `client.py`'s `renew()` to ensure `LeaseRenewalResponse.cancel_requested` deserializes correctly (should be automatic via Pydantic model update, but add a test).
+- [x] 4.4 Update `AssignmentExecutor._execute_goal()` and `_execute_workflow()` (`host_agent/assignment.py`) to map a cancellation-flavored stop to `AssignmentExecutionResult.status = "cancelled"` (new value alongside `"done"`/`"failed"`), reading the underlying `Task`/`WorkflowRun` status (`"cancelled"`) instead of collapsing it to `"failed"`.
+- [x] 4.5 Update `AssignmentProcessor.process()` (`host_agent/processor.py`) so its `status = "done" if execution.status == "done" else "failed"` mapping becomes a three-way mapping that preserves `"cancelled"`, and `report_result` is called with `status="cancelled"` in that case.
+- [x] 4.6 Add/extend Host Agent tests covering: a renewal response with `cancel_requested=True` stops the active `should_stop`-driven loop; the resulting `AssignmentExecutionResult.status` and reported terminal status are `"cancelled"`; a lease-loss stop unrelated to cancellation still reports `"failed"`.
 
 ## 5. Public SDK endpoint
 

tests/test_host_agent_progress_reporting.py

@@ -58,6 +58,7 @@ class _FakeExecutor:
         assignment: AssignmentModel,
         *,
         should_stop: Any | None = None,
+        stop_reason: Any | None = None,
     ) -> Any:
         from host_agent.assignment import AssignmentExecutionResult