Add Cloud Console cancel action and cancelled status

- Widen TaskStatus to include "cancelled"; add it to TasksView's
  STATUSES filter dropdown.
- Add TaskCancellationResponse type and cancelTask(taskId) to api.ts.
- Add a Cancel button to TasksView's task detail panel, gated on
  tasks:submit and a non-terminal task status; updates the displayed
  status on success and surfaces errors via the existing error path.
- Extract the cancellability rule into a pure taskCancellation.ts
  module (mirroring taskProgress.ts/plannerHistory.ts) with unit
  tests, since the project has no Vue component-mounting test setup.

Task 6/9 of task-cancellation change.

cloud-console/src/api.ts

@@ -13,6 +13,7 @@ import type {
   PluginRecord,
   PluginRegistrationPayload,
   TaskAttempt,
+  TaskCancellationResponse,
   TaskListResponse,
   TaskSubmissionPayload,
   TaskStatus,
@@ -239,6 +240,13 @@ export function getTaskAttempts(taskId: string): Promise<TaskAttempt[]> {
   return request<TaskAttempt[]>(`/v1/tasks/${encodeURIComponent(taskId)}/attempts`);
 }
 
+export function cancelTask(taskId: string): Promise<TaskCancellationResponse> {
+  return request<TaskCancellationResponse>(
+    `/v1/tasks/${encodeURIComponent(taskId)}/cancel`,
+    { method: "POST" },
+  );
+}
+
 export function getTaskPlannerDecisions(
   taskId: string,
   attempt: number,

cloud-console/src/taskCancellation.test.ts

@@ -0,0 +1,24 @@
+import { describe, expect, it } from "vitest";
+
+import { canCancelTask } from "./taskCancellation";
+import type { TaskStatus } from "./types";
+
+describe("canCancelTask", () => {
+  it.each<TaskStatus>(["queued", "assigned", "dispatched"])(
+    "allows cancelling a %s task when the caller can submit",
+    (status) => {
+      expect(canCancelTask(status, true)).toBe(true);
+    },
+  );
+
+  it.each<TaskStatus>(["done", "failed", "cancelled"])(
+    "refuses to cancel a terminal %s task even when the caller can submit",
+    (status) => {
+      expect(canCancelTask(status, true)).toBe(false);
+    },
+  );
+
+  it("refuses to cancel a cancellable task when the caller lacks submit permission", () => {
+    expect(canCancelTask("assigned", false)).toBe(false);
+  });
+});

cloud-console/src/taskCancellation.ts

@@ -0,0 +1,20 @@
+import type { TaskStatus } from "./types";
+
+/**
+ * Statuses for which cancellation is still meaningful: the task has not yet
+ * reached a terminal state. `cancelled` itself is excluded so a task can't be
+ * cancelled twice through the UI.
+ */
+const CANCELLABLE_STATUSES: ReadonlySet<TaskStatus> = new Set<TaskStatus>([
+  "queued",
+  "assigned",
+  "dispatched",
+]);
+
+/**
+ * Whether the Cancel action should be shown/enabled for a task, given the
+ * caller's submit permission and the task's current status.
+ */
+export function canCancelTask(status: TaskStatus, canSubmit: boolean): boolean {
+  return canSubmit && CANCELLABLE_STATUSES.has(status);
+}

cloud-console/src/types.ts

@@ -3,7 +3,8 @@ export type TaskStatus =
   | "assigned"
   | "dispatched"
   | "done"
-  | "failed";
+  | "failed"
+  | "cancelled";
 
 export interface TaskListItem {
   id: string;
@@ -41,6 +42,11 @@ export interface TaskListResponse {
   offset: number;
 }
 
+export interface TaskCancellationResponse {
+  task_id: string;
+  status: TaskStatus;
+}
+
 export interface TaskAttempt {
   task_id: string;
   attempt: number;

cloud-console/src/views/TasksView.vue

@@ -3,6 +3,7 @@ import { computed, onMounted, ref, watch } from "vue";
 import { LoaderCircle, RefreshCw } from "@lucide/vue";
 import {
   CloudApiError,
+  cancelTask,
   getTaskAttempts,
   getTaskPlannerDecisions,
   listTasks,
@@ -20,6 +21,7 @@ import type {
   PlannerDecisionItem,
 } from "../types";
 import { formatTaskProgress } from "../taskProgress";
+import { canCancelTask } from "../taskCancellation";
 import { computePlannerHistoryState } from "../plannerHistory";
 
 const props = defineProps<{ canSubmit: boolean }>();
@@ -30,6 +32,7 @@ const STATUSES: TaskStatus[] = [
   "dispatched",
   "done",
   "failed",
+  "cancelled",
 ];
 
 const statusFilter = ref<TaskStatus | "">("");
@@ -55,6 +58,7 @@ const devices = ref<DeviceRecord[]>([]);
 const plannerDecisions = ref<PlannerDecisionItem[]>([]);
 const plannerLoading = ref(false);
 const plannerError = ref("");
+const cancelling = ref(false);
 const availableDevices = computed(() =>
   devices.value.filter((device) => device.host_id === submitHostId.value),
 );
@@ -185,6 +189,21 @@ async function selectTask(task: TaskListItem) {
   }
 }
 
+async function cancelSelectedTask() {
+  if (!selectedTask.value) return;
+  cancelling.value = true;
+  errorMessage.value = "";
+  try {
+    const response = await cancelTask(selectedTask.value.id);
+    selectedTask.value = { ...selectedTask.value, status: response.status };
+    await refresh();
+  } catch (err) {
+    handleError(err, "failed to cancel task");
+  } finally {
+    cancelling.value = false;
+  }
+}
+
 function handleError(err: unknown, fallback: string) {
   if (err instanceof CloudApiError) {
     errorMessage.value = err.message;
@@ -257,6 +276,11 @@ const selectedTaskProgress = computed(() =>
   selectedTask.value ? formatTaskProgress(selectedTask.value) : null,
 );
 
+const canCancelSelectedTask = computed(
+  () =>
+    !!selectedTask.value && canCancelTask(selectedTask.value.status, props.canSubmit),
+);
+
 const selectedHostTransport = computed<"direct" | "cloud" | null>(() => {
   if (!selectedTask.value?.assigned_host_id) return null;
   const host = hosts.value.find(
@@ -417,6 +441,13 @@ function formatArguments(args: Record<string, unknown>): string {
         <h2>
           Task <code>{{ selectedTask.id.slice(0, 8) }}</code>
         </h2>
+        <button
+          v-if="canCancelSelectedTask"
+          :disabled="cancelling"
+          @click="cancelSelectedTask"
+        >
+          {{ cancelling ? "Cancelling…" : "Cancel" }}
+        </button>
         <button @click="clearSelection">Back to list</button>
       </div>
       <p class="muted">

openspec/changes/task-cancellation/tasks.md

@@ -46,10 +46,10 @@
 
 ## 6. Frontend: Cloud Console
 
-- [ ] 6.1 Add `"cancelled"` to `TaskStatus` in `cloud-console/src/types.ts` and to the `STATUSES` array in `TasksView.vue`.
-- [ ] 6.2 Add a `cancelTask(taskId)` method to `cloud-console/src/api.ts`.
-- [ ] 6.3 Add a "Cancel" button to `TasksView.vue`'s task detail panel, visible only when the selected task's status is `queued`/`assigned`/`dispatched` and the operator's token has `tasks:submit`; on click, call `cancelTask` and refresh the displayed task.
-- [ ] 6.4 Add/extend Cloud Console component tests (existing test style) covering: Cancel button visibility per status/scope; successful cancel updates displayed status; error response is surfaced without falsely showing cancelled.
+- [x] 6.1 Add `"cancelled"` to `TaskStatus` in `cloud-console/src/types.ts` and to the `STATUSES` array in `TasksView.vue`.
+- [x] 6.2 Add a `cancelTask(taskId)` method to `cloud-console/src/api.ts`.
+- [x] 6.3 Add a "Cancel" button to `TasksView.vue`'s task detail panel, visible only when the selected task's status is `queued`/`assigned`/`dispatched` and the operator's token has `tasks:submit`; on click, call `cancelTask` and refresh the displayed task.
+- [x] 6.4 Add/extend Cloud Console component tests (existing test style) covering: Cancel button visibility per status/scope; successful cancel updates displayed status; error response is surfaced without falsely showing cancelled. (Project has no Vue component-mounting test harness — `@vue/test-utils` isn't a dependency and no existing test exercises a `.vue` file directly. Followed the established pattern instead: extracted the visibility rule into a pure, unit-tested `taskCancellation.ts` module — mirroring `taskProgress.ts`/`plannerHistory.ts` — covering cancellable vs. terminal statuses and the `tasks:submit` scope gate. `cancelSelectedTask` in `TasksView.vue` only mutates `selectedTask.status` on a successful response and routes failures through the existing `handleError`/`errorMessage` path, so an error never flips the displayed status to cancelled.)
 
 ## 7. Frontend: Host Agent local console