Fix #4896: Orchestrator subtask cancellation fails to return to parent task after API streaming error

[roomote]

When an API streaming error occurs in a subtask, instead of reinitializing
the subtask with history (which keeps it stuck in subtask view), properly
return control to the parent task by calling finishSubTask().

This ensures that orchestrator mode can properly resume the parent task
after a subtask encounters an API streaming failure during cancellation.

---

Important

Fixes subtask cancellation in orchestrator mode by returning control to the parent task after an API streaming error in Task.ts.

• Behavior:
  • In Task.ts, modify error handling for API streaming errors in subtasks.
  • If a subtask encounters an API streaming error, call finishSubTask() to return control to the parent task.
  • For main tasks, continue to reinitialize with history as before.
• Error Handling:
  • Specifically addresses API streaming failures during subtask cancellation in orchestrator mode.

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[daniel-lxs]

Testing shows this fix doesn't resolve the issue. When canceling a subtask during the thinking phase and clicking X, the task still doesn't return to the parent orchestrator task as expected.

The problem appears to be that finishSubTask is already being called through the clearTask handler when clicking X, but the parent task isn't resuming. Adding another finishSubTask call in the API streaming error handler doesn't address the root cause.

Closing this PR as it doesn't fix the reported issue.