diff --git a/src/features/background-agent/manager.test.ts b/src/features/background-agent/manager.test.ts
index 8e275a6d..5d0de3f6 100644
--- a/src/features/background-agent/manager.test.ts
+++ b/src/features/background-agent/manager.test.ts
@@ -1060,3 +1060,253 @@ describe("BackgroundManager process cleanup", () => {
   })
 })
 
+describe("BackgroundManager.checkAndInterruptStaleTasks", () => {
+  test("should NOT interrupt task running less than 30 seconds (min runtime guard)", async () => {
+    const client = {
+      session: {
+        prompt: async () => ({}),
+        abort: async () => ({}),
+      },
+    }
+    const manager = new BackgroundManager({ client, directory: tmpdir() } as unknown as PluginInput, { staleTimeoutMs: 180_000 })
+
+    const task: BackgroundTask = {
+      id: "task-1",
+      sessionID: "session-1",
+      parentSessionID: "parent-1",
+      parentMessageID: "msg-1",
+      description: "Test task",
+      prompt: "Test",
+      agent: "test-agent",
+      status: "running",
+      startedAt: new Date(Date.now() - 20_000),
+      progress: {
+        toolCalls: 0,
+        lastUpdate: new Date(Date.now() - 200_000),
+      },
+    }
+
+    manager["tasks"].set(task.id, task)
+
+    await manager["checkAndInterruptStaleTasks"]()
+
+    expect(task.status).toBe("running")
+  })
+
+  test("should NOT interrupt task with recent lastUpdate", async () => {
+    const client = {
+      session: {
+        prompt: async () => ({}),
+        abort: async () => ({}),
+      },
+    }
+    const manager = new BackgroundManager({ client, directory: tmpdir() } as unknown as PluginInput, { staleTimeoutMs: 180_000 })
+
+    const task: BackgroundTask = {
+      id: "task-2",
+      sessionID: "session-2",
+      parentSessionID: "parent-2",
+      parentMessageID: "msg-2",
+      description: "Test task",
+      prompt: "Test",
+      agent: "test-agent",
+      status: "running",
+      startedAt: new Date(Date.now() - 60_000),
+      progress: {
+        toolCalls: 5,
+        lastUpdate: new Date(Date.now() - 30_000),
+      },
+    }
+
+    manager["tasks"].set(task.id, task)
+
+    await manager["checkAndInterruptStaleTasks"]()
+
+    expect(task.status).toBe("running")
+  })
+
+  test("should interrupt task with stale lastUpdate (> 3min)", async () => {
+    const client = {
+      session: {
+        prompt: async () => ({}),
+        abort: async () => ({}),
+      },
+    }
+    const manager = new BackgroundManager({ client, directory: tmpdir() } as unknown as PluginInput, { staleTimeoutMs: 180_000 })
+
+    const task: BackgroundTask = {
+      id: "task-3",
+      sessionID: "session-3",
+      parentSessionID: "parent-3",
+      parentMessageID: "msg-3",
+      description: "Stale task",
+      prompt: "Test",
+      agent: "test-agent",
+      status: "running",
+      startedAt: new Date(Date.now() - 300_000),
+      progress: {
+        toolCalls: 2,
+        lastUpdate: new Date(Date.now() - 200_000),
+      },
+    }
+
+    manager["tasks"].set(task.id, task)
+
+    await manager["checkAndInterruptStaleTasks"]()
+
+    expect(task.status).toBe("cancelled")
+    expect(task.error).toContain("Stale timeout")
+    expect(task.error).toContain("3min")
+    expect(task.completedAt).toBeDefined()
+  })
+
+  test("should respect custom staleTimeoutMs config", async () => {
+    const client = {
+      session: {
+        prompt: async () => ({}),
+        abort: async () => ({}),
+      },
+    }
+    const manager = new BackgroundManager({ client, directory: tmpdir() } as unknown as PluginInput, { staleTimeoutMs: 60_000 })
+
+    const task: BackgroundTask = {
+      id: "task-4",
+      sessionID: "session-4",
+      parentSessionID: "parent-4",
+      parentMessageID: "msg-4",
+      description: "Custom timeout task",
+      prompt: "Test",
+      agent: "test-agent",
+      status: "running",
+      startedAt: new Date(Date.now() - 120_000),
+      progress: {
+        toolCalls: 1,
+        lastUpdate: new Date(Date.now() - 90_000),
+      },
+    }
+
+    manager["tasks"].set(task.id, task)
+
+    await manager["checkAndInterruptStaleTasks"]()
+
+    expect(task.status).toBe("cancelled")
+    expect(task.error).toContain("Stale timeout")
+  })
+
+  test("should release concurrency before abort", async () => {
+    const client = {
+      session: {
+        prompt: async () => ({}),
+        abort: async () => ({}),
+      },
+    }
+    const manager = new BackgroundManager({ client, directory: tmpdir() } as unknown as PluginInput, { staleTimeoutMs: 180_000 })
+
+    const task: BackgroundTask = {
+      id: "task-5",
+      sessionID: "session-5",
+      parentSessionID: "parent-5",
+      parentMessageID: "msg-5",
+      description: "Concurrency test",
+      prompt: "Test",
+      agent: "test-agent",
+      status: "running",
+      startedAt: new Date(Date.now() - 300_000),
+      progress: {
+        toolCalls: 1,
+        lastUpdate: new Date(Date.now() - 200_000),
+      },
+      concurrencyKey: "test-agent",
+    }
+
+    manager["tasks"].set(task.id, task)
+
+    await manager["checkAndInterruptStaleTasks"]()
+
+    expect(task.concurrencyKey).toBeUndefined()
+    expect(task.status).toBe("cancelled")
+  })
+
+  test("should handle multiple stale tasks in same poll cycle", async () => {
+    const client = {
+      session: {
+        prompt: async () => ({}),
+        abort: async () => ({}),
+      },
+    }
+    const manager = new BackgroundManager({ client, directory: tmpdir() } as unknown as PluginInput, { staleTimeoutMs: 180_000 })
+
+    const task1: BackgroundTask = {
+      id: "task-6",
+      sessionID: "session-6",
+      parentSessionID: "parent-6",
+      parentMessageID: "msg-6",
+      description: "Stale 1",
+      prompt: "Test",
+      agent: "test-agent",
+      status: "running",
+      startedAt: new Date(Date.now() - 300_000),
+      progress: {
+        toolCalls: 1,
+        lastUpdate: new Date(Date.now() - 200_000),
+      },
+    }
+
+    const task2: BackgroundTask = {
+      id: "task-7",
+      sessionID: "session-7",
+      parentSessionID: "parent-7",
+      parentMessageID: "msg-7",
+      description: "Stale 2",
+      prompt: "Test",
+      agent: "test-agent",
+      status: "running",
+      startedAt: new Date(Date.now() - 400_000),
+      progress: {
+        toolCalls: 2,
+        lastUpdate: new Date(Date.now() - 250_000),
+      },
+    }
+
+    manager["tasks"].set(task1.id, task1)
+    manager["tasks"].set(task2.id, task2)
+
+    await manager["checkAndInterruptStaleTasks"]()
+
+    expect(task1.status).toBe("cancelled")
+    expect(task2.status).toBe("cancelled")
+  })
+
+  test("should use default timeout when config not provided", async () => {
+    const client = {
+      session: {
+        prompt: async () => ({}),
+        abort: async () => ({}),
+      },
+    }
+    const manager = new BackgroundManager({ client, directory: tmpdir() } as unknown as PluginInput)
+
+    const task: BackgroundTask = {
+      id: "task-8",
+      sessionID: "session-8",
+      parentSessionID: "parent-8",
+      parentMessageID: "msg-8",
+      description: "Default timeout",
+      prompt: "Test",
+      agent: "test-agent",
+      status: "running",
+      startedAt: new Date(Date.now() - 300_000),
+      progress: {
+        toolCalls: 1,
+        lastUpdate: new Date(Date.now() - 200_000),
+      },
+    }
+
+    manager["tasks"].set(task.id, task)
+
+    await manager["checkAndInterruptStaleTasks"]()
+
+    expect(task.status).toBe("cancelled")
+  })
+})
+