[kevmo314]

Summary

has_expired() reads self._expire_at twice:

keepalive_expired = self._expire_at is not None and now > self._expire_at

If another thread starts a request on the connection between the two reads, handle_request() sets _expire_at to None and the comparison raises:

TypeError: '>' not supported between instances of 'float' and 'NoneType'

This is easy to hit on free-threaded Python 3.14t, for example when huggingface_hub downloads files on a thread pool with one shared client. The fix reads _expire_at once, in the HTTP/1.1 and HTTP/2 connections, sync and async. New tests simulate the interleaving; they fail before the change and pass after.

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.