Function backgroundTask

src/tasks/LocalShellTask/LocalShellTask.tsx:293–368

* Background a specific foreground task. * @returns true if backgrounded successfully, false otherwise

(taskId: string, getAppState: () => AppState, setAppState: SetAppState)

 * @returns true if backgrounded successfully, false otherwise
 */
function backgroundTask(taskId: string, getAppState: () => AppState, setAppState: SetAppState): boolean {
  // Step 1: Get the task and shell command from current state
  const state = getAppState();
  const task = state.tasks[taskId];
  if (!isLocalShellTask(task) || task.isBackgrounded || !task.shellCommand) {
    return false;
  }
  const shellCommand = task.shellCommand;
  const description = task.description;
  const {
    toolUseId,
    kind,
    agentId
  } = task;

  // Transition to backgrounded — TaskOutput continues receiving data automatically
  if (!shellCommand.background(taskId)) {
    return false;
  }
  setAppState(prev => {
    const prevTask = prev.tasks[taskId];
    if (!isLocalShellTask(prevTask) || prevTask.isBackgrounded) {
      return prev;
    }
    return {
      ...prev,
      tasks: {
        ...prev.tasks,
        [taskId]: {
          ...prevTask,
          isBackgrounded: true
        }
      }
    };
  });
  const cancelStallWatchdog = startStallWatchdog(taskId, description, kind, toolUseId, agentId);

  // Set up result handler
  void shellCommand.result.then(async result => {
    cancelStallWatchdog();
    await flushAndCleanup(shellCommand);
    let wasKilled = false;
    let cleanupFn: (() => void) | undefined;
    updateTaskState<LocalShellTaskState>(taskId, setAppState, t => {
      if (t.status === 'killed') {
        wasKilled = true;
        return t;
      }

      // Capture cleanup function to call outside of updater
      cleanupFn = t.unregisterCleanup;
      return {
        ...t,
        status: result.code === 0 ? 'completed' : 'failed',
        result: {
          code: result.code,
          interrupted: result.interrupted
        },