Fail-fast on prompt_worker crash (prevent “accept but not execute”)

[lixiang007666]

Reason

We reproduced a scenario where an exception triggers handle_execution_error and the code path accesses:

class_type = prompt[node_id]["class_type"]

If the reported node_id is modified to a non-existent ID, this lookup can raise (e.g., KeyError), causing the
prompt_worker thread to crash.

After that, ComfyUI still appears to accept requests and successfully put them into the queue
("got prompt" looks normal), but since prompt_worker is no longer alive, the queue is never consumed.

This results in a silent “accept but not execute” state.

This PR is done:

The goal of this PR is to prevent ComfyUI from getting into a state where it accepts requests but does not process them, by adopting a fail-fast that terminates the process immediately.

[lixiang007666]

@Kosinkadink @guill @comfyanonymous
I’d appreciate it if you could take some time to review this PR.

[rattus128]

Curious, what happens in your test case if you infinite loop here?

Instead of os._exit() if you just while(True) with your exception discard does is recover?

[lixiang007666]

Good point.
In fact, by the time we reach os._exit(), the prompt_worker thread is already no longer alive. If we replace os._exit() with while True, the process won’t exit; requests will continue to be enqueued, but the queue will never be consumed.