Support debugging of indirect child processes.

まず、言及されているエントリポイント debugpy.server.cli.options、debugpy.server.api、debugpy.connect を確認し、既存の直接の子プロセスに対するマルチプロセス対応と比較します。間接的な非 Python プロセスを介してセッションコンテキストを引き渡すための公式な API 境界を定義します。示されている多段階のワーカーツリーが実装の詳細に依存せず接続できれば完了です。

While debugpy natively supports multiprocess debugging, this works only for directly launched child processes.
Sometimes, though, there may be several levels on non-Python processes between the main process and the child one needs to debug. I am hitting this limitation while trying to debug a user-defined function, that runs in the context of a PySpark worker process. The process tree looks like this:

<python process hosting my main program>
 └ <pyspark process>
    └ <yet another pyspark process>
       ├ <python worker process hosting the UDFs>
       ├ <python worker process hosting the UDFs>
       ├ ...
       └ <python worker process hosting the UDFs>

After spelunking the innards of debugpy for a few hours, I've managed to come up with this code:

import pickle
import os
import debugpy

def capture_session_context():
    """To be called in the main process to capture context of the current debugpy session."""
    options = debugpy.server.cli.options
    context = pickle.dumps((options.address, options.adapter_access_token, os.getpid()), 0)
    os.environ["DEBUGPY_CONTEXT"] = context.decode('ascii')

def connect_to_session():
    """To be called in a worker process to connect to the parent session."""
    context = os.environ['DEBUGPY_CONTEXT'].encode('ascii')
    address, token, ppid = pickle.loads(context)
    from debugpy.server import api
    api.pydevd.SetupHolder.setup = {"ppid": ppid}
    debugpy.connect(address, access_token=token)

Obviously, this hack uses a bunch of implementation details. It would be nice if this scenario was officially supported.
(I mean exposing official APIs similar to the above, not that debugpy should support PySperk specifically.