fix(agent): skip OpenAI client rebuild for Anthropic-mode providers (#44006)

[kyssta-exe]

Fixes #44006. Skip the OpenAI client rebuild in _replace_primary_openai_client when the provider uses the Anthropic adapter (e.g. minimax). These providers have client=None and _client_kwargs={}; attempting to rebuild would always fail with 'api_key must be set', masking the real retry logic and causing stream timeouts to drop the entire response.

[alt-glitch]

Duplicate of #36719 (open) — same approach: short-circuit _replace_primary_openai_client in run_agent.py for anthropic_messages providers (client=None). #44076 takes a different mechanism (rebuild the Anthropic client) for the same #44006.

[liuhao1024]

Code review: clean ✅

The early-return guard in _replace_primary_openai_client is correctly scoped. Verified:

1. The condition (not getattr(self, "client", None) and not self._client_kwargs.get("api_key")) matches exactly the providers that don'''t use an OpenAI client — both the client object and the API key must be absent.
2. Returning False (instead of raising) preserves the retry logic flow — callers already handle the False return.
3. The fix is minimal and targeted — no behavioral change for providers that DO use OpenAI clients.

No issues found.

[kyssta-exe]

Duplicate of #36719 — same OpenAI client rebuild skip for Anthropic providers (#44006). Closing as superseded.