After a client replacement (credential rotation, dead-connection cleanup,
or fallback+restore), agent.client may become a native OpenAI client
while agent.provider stays "moa". The _moa_prepared_request key was
passed through to the native SDK, causing TypeError on every turn.
Pop the key at the dispatch point (chat_completion_helpers.py:509).
The MoAClient facade already handles a missing key by falling through
to its normal resolution path.
Closes#78382
RelaxJonh