fix(stream): rebuild Anthropic client on stream retry, not the OpenAI client

[AIalliAI]

Fixes #44006

Problem

When a provider stream drops mid-generation, the retry path in interruptible_streaming_api_call unconditionally calls _replace_primary_openai_client(reason="stream_retry_pool_cleanup") to purge dead connections before retrying.

In anthropic_messages mode this is wrong on both counts:

1. The rebuild always fails. Hermes routes MiniMax (and other third-party Anthropic-protocol providers) through the Anthropic SDK; in this mode agent.client is None and agent._client_kwargs == {} by design. The rebuild constructs OpenAI(**{}), which raises exactly the error in the issue report: The api_key client option must be set .... This is why the failure log says the rebuilt client "has no api_key" — there was never an OpenAI client (or kwargs) to rebuild in this mode.

2. The client that actually carried the stream is never cleaned. The dropped connection lives in agent._anthropic_client's httpx pool, where the retry can pick it right back up and time out again — losing the generation. The per-attempt _try_refresh_anthropic_client_credentials call doesn't cover this either: it returns early for non-native providers (provider != "anthropic") and only rebuilds when the token actually rotated.

Fix

• Add AIAgent._replace_primary_anthropic_client(reason=...) — the Anthropic-protocol analog of _replace_primary_openai_client: rebuilds the shared Anthropic client with the same credentials/base_url/timeout, swapping in a fresh connection pool, and closes the old client. On rebuild failure the old client is kept and False is returned (mirrors the OpenAI variant).
• Make both stream-retry cleanup sites (stream_retry_pool_cleanup and stream_mid_tool_retry_pool_cleanup) mode-aware: rebuild the Anthropic client in anthropic_messages mode, the shared OpenAI client otherwise.

OpenAI-wire (chat_completions) behavior is unchanged.

Tests

• New TestReplacePrimaryAnthropicClient covering: rebuild uses the same credentials and closes the old client; failed rebuild keeps the old client; no-op outside anthropic_messages mode; no-op when no Anthropic client exists.
• Updated test_anthropic_stream_parser_valueerror_retries_before_delivery (which reproduces the issue's exact setup — MiniMax via api.minimax.io/anthropic) to assert the retry now purges the Anthropic pool and never attempts the doomed OpenAI rebuild.
• tests/run_agent/: 1624 passed, 3 skipped. The two test_provider_parity.py::TestAuxiliaryClientProviderPriority failures in the full-suite run are pre-existing on main (order-dependent; both pass in isolation on main and on this branch).

[liuhao1024]

Verification: reviewed diff — clean fix.

The new _replace_primary_anthropic_client() method mirrors the existing _replace_primary_openai_client() pattern correctly:

• Guards on api_mode == "anthropic_messages" and non-None _anthropic_client
• Rebuilds via build_anthropic_client() with the same credentials (key + base_url + timeout)
• Closes old client after successful swap; keeps old client on build failure
• All exceptions caught and logged

The two call sites in chat_completion_helpers.py (mid-tool retry at L2338 and stream retry at L2396) now branch on api_mode to rebuild the correct client. Previously both paths unconditionally called _replace_primary_openai_client(), which in anthropic_messages mode has empty _client_kwargs and silently fails — leaving the dead connection in the Anthropic httpx pool for the retry to hit again.

Test updates are well-aligned:

• test_anthropic_stream_parser_valueerror_retries_before_delivery now asserts the Anthropic mock is called (not the OpenAI mock)
• New TestReplacePrimaryAnthropicClient class covers: rebuild with same credentials, keeps old client on build failure, no-op outside anthropic mode, no-op without anthropic client

[AIalliAI]

Requesting maintainer review — this is ready to land from my side. Standalone fork CI is pending first-run approval here; the rollup branch in #44061 carrying this session's batch is fully green on upstream CI (all test shards, typecheck, e2e).

[AIalliAI]

@teknium1 mind reviewing? In anthropic_messages mode the stream/mid-tool retry path was rebuilding the OpenAI client (which silently no-ops) and reusing the dead Anthropic httpx connection — this adds _replace_primary_anthropic_client() and branches the two retry call sites on api_mode.

[teknium1]

Closed in favor of #53926, now merged to main (commit a0b9663).

This was a popular bug — 12 independent PRs fixed the same issue (#28161): the three stream-cleanup paths in the streaming code rebuilt the OpenAI primary client unconditionally, which on Anthropic-native sessions both failed (no OPENAI_API_KEY) and left the wedged stream open, causing the ~15-minute hang.

We salvaged @EloquentBrush0x's #28240 (the earliest dedicated fix for this issue) onto current main, resolved the conflict against the newer request-client cleanup helper, repointed the bug-encoding regression test, and added coverage for the two reachable Anthropic cleanup sites. Verified live: stale stream torn down in <1s instead of ~900s, Anthropic client closed+rebuilt, OpenAI rebuild never called on the Anthropic path.

Thank you for the fix — closing as a duplicate of the merged work. Credit to everyone who reported and fixed this.

#53926