In resolve_provider_client(), the named custom provider code path at
~line 2914 only checked the ``key_env`` field when looking for an
environment-variable-based API key. The documented ``api_key_env``
snake_case alias was silently ignored, causing custom providers
configured with ``api_key_env`` to fall through to the
``no-key-required`` placeholder — which produces a confusing 401
(``****ired`` mask) on auth-required remote endpoints.
This mirrors the same fix already applied to run_agent.py in commit
6ddc48b05 (fix(fallback): resolve api_key_env in fallback chain entries).
Also adds a logger.warning() when the placeholder is reached, so
future alias gaps are easier to debug.
Closes#25091
b389796ae3