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"