fix(background-cancel): skip notification when user explicitly cancels tasks

- Add skipNotification option to cancelTask method
- Apply skipNotification to background_cancel tool
- Prevents unwanted notifications when user cancels via tool

src/tools/background-task/tools.test.ts

@@ -328,6 +328,58 @@ describe("background_cancel", () => {
     expect(output).toContain("| `task-a` | running task | running | `ses-a` |")
     expect(output).toContain("| `task-b` | pending task | pending | (not started) |")
   })
+
+  test("passes skipNotification: true to cancelTask to prevent deadlock", async () => {
+    // #given
+    const task = createTask({ id: "task-1", status: "running" })
+    const cancelOptions: Array<{ taskId: string; options: unknown }> = []
+    const manager = {
+      getTask: (id: string) => (id === task.id ? task : undefined),
+      getAllDescendantTasks: () => [task],
+      cancelTask: async (taskId: string, options?: unknown) => {
+        cancelOptions.push({ taskId, options })
+        task.status = "cancelled"
+        return true
+      },
+    } as unknown as BackgroundManager
+    const client = { session: { abort: async () => ({}) } } as BackgroundCancelClient
+    const tool = createBackgroundCancel(manager, client)
+
+    // #when - cancel all tasks
+    await tool.execute({ all: true }, mockContext)
+
+    // #then - skipNotification should be true to prevent self-deadlock
+    expect(cancelOptions).toHaveLength(1)
+    expect(cancelOptions[0].options).toEqual(
+      expect.objectContaining({ skipNotification: true })
+    )
+  })
+
+  test("passes skipNotification: true when cancelling single task", async () => {
+    // #given
+    const task = createTask({ id: "task-1", status: "running" })
+    const cancelOptions: Array<{ taskId: string; options: unknown }> = []
+    const manager = {
+      getTask: (id: string) => (id === task.id ? task : undefined),
+      getAllDescendantTasks: () => [task],
+      cancelTask: async (taskId: string, options?: unknown) => {
+        cancelOptions.push({ taskId, options })
+        task.status = "cancelled"
+        return true
+      },
+    } as unknown as BackgroundManager
+    const client = { session: { abort: async () => ({}) } } as BackgroundCancelClient
+    const tool = createBackgroundCancel(manager, client)
+
+    // #when - cancel single task
+    await tool.execute({ taskId: task.id }, mockContext)
+
+    // #then - skipNotification should be true
+    expect(cancelOptions).toHaveLength(1)
+    expect(cancelOptions[0].options).toEqual(
+      expect.objectContaining({ skipNotification: true })
+    )
+  })
 })
 type BackgroundOutputMessage = {
   id?: string

src/tools/background-task/tools.ts

@@ -642,6 +642,7 @@ export function createBackgroundCancel(manager: BackgroundManager, client: Backg
             const cancelled = await manager.cancelTask(task.id, {
               source: "background_cancel",
               abortSession: originalStatus === "running",
+              skipNotification: true,
             })
             if (!cancelled) continue
             cancelledInfo.push({
@@ -690,6 +691,7 @@ Only running or pending tasks can be cancelled.`
         const cancelled = await manager.cancelTask(task.id, {
           source: "background_cancel",
           abortSession: task.status === "running",
+          skipNotification: true,
         })
         if (!cancelled) {
           return `[ERROR] Failed to cancel task: ${task.id}`