Stale connection stays in pool after ConnectionNotAvailable #1066

_async/connection_pool.py around line 245 — on ConnectionNotAvailable, pool_request.clear_connection() removes the connection from the request but doesn't remove it from the pool. The connection is only removed later if is_closed() or has_expired() returns true.

If neither condition is met, the connection stays in the pool and can be handed out again, causing repeated ConnectionNotAvailable.