fix(auxiliary): keep /anthropic base_url for anthropic_messages custom endpoints

[AlexanderPrendota]

What does this PR do?

The custom + explicit_base_url branch of resolve_provider_client() (in agent/auxiliary_client.py) rewrote a trailing /anthropic to /v1 via _to_openai_base_url() and then passed that rewritten base to the wrap-decision (_wrap_if_needed → _maybe_wrap_anthropic) — even when api_mode was anthropic_messages. The Anthropic wrapper therefore never saw the real /anthropic path, so for any custom provider whose base_url ends in /anthropic (a proxied Anthropic gateway — MiniMax, Zhipu/GLM, a LiteLLM proxy, or a self-hosted LLM proxy) every auxiliary task (title generation, compression, vision, web_extract, session_search) hit .../v1/chat/completions on a Messages-only endpoint and failed.

Fix

Guard the wrap base on api_mode: for api_mode == "anthropic_messages" the Anthropic wrapper is built on the raw /anthropic base, while the plain OpenAI client — and the OpenAI-wire fallback taken when the anthropic SDK is unavailable — still uses the /v1-rewritten base so it never lands on /anthropic/chat/completions. The change is scoped: it adds a wrap_base that equals custom_base on every existing path (including the main_runtime named-custom path) and only differs for the explicit-base anthropic_messages case. Non-anthropic paths are unchanged.

Ships with focused regression tests (tests/agent/test_auxiliary_explicit_base_anthropic.py): raw /anthropic base is preserved for the wrapper, the OpenAI-wire fallback stays on /v1, and the non-anthropic /anthropic→/v1 rewrite is untouched.

Related

Root cause: #16254 (duplicate: #17086).

A few open PRs already target the same _to_openai_base_url() /anthropic→/v1 rewrite:

• fix(auxiliary): skip /anthropic to /v1 rewrite when api_mode is anthropic_messages #61333 — skip the rewrite when api_mode is anthropic_messages (closest to this PR)
• fix(auxiliary): preserve /anthropic base_url for custom vision provider with anthropic_messages api_mode #60753 — preserve /anthropic base_url for the custom vision provider with anthropic_messages
• fix(providers): skip /anthropic rewrite for sub-application paths like /apps/anthropic #61394 — skip the rewrite for sub-application paths like /apps/anthropic

How this PR differs: it guards the wrap base in the custom + explicit_base_url branch (the path _resolve_auto Step 1 uses for a custom main provider), and it keeps the /v1 rewrite for the OpenAI-wire fallback so that fallback never lands on /anthropic/chat/completions.

Refs #16254

Type of Change

• 🐛 Bug fix (non-breaking change that fixes an issue)

[teknium1]

Thanks for the focused regression fix. The premise is confirmed on current main: agent/auxiliary_client.py:4796 rewrites an explicit custom /anthropic URL before agent/auxiliary_client.py:4853 supplies it to _wrap_if_needed. _maybe_wrap_anthropic then passes that supplied URL directly to build_anthropic_client (agent/auxiliary_client.py:1642-1675).

The proposed wrap_base keeps the native Anthropic wrapper on the raw endpoint while preserving the rewritten OpenAI client for the SDK-unavailable fallback. This matches the existing named-custom-provider handling at agent/auxiliary_client.py:4916-4958. The regression tests cover the native wrapper, fallback, and non-Anthropic behavior.

Automated hermes-sweeper review.

[teknium1]

Merged via PR #85466 with your commit cherry-picked onto current main — authorship preserved in git log. The keep-/v1-for-fallback nuance in your version was the cleanest of the cluster fixes for this branch. The sibling paths you enumerated (#60753 vision, #61333 class-wide guard) are being evaluated as one cluster decision on top of this. Thanks!