fix(auth): use bearer auth for MiniMax Anthropic endpoints

[kshitijk4poor]

Problem

MiniMax's Anthropic-compatible /anthropic endpoints were failing with HTTP 401 authentication errors in Hermes gateway sessions even when MINIMAX_API_KEY was configured correctly.

The user-visible failure matched MiniMax's auth error exactly:

• login fail: Please carry the API secret key in the 'Authorization' field of the request header

This broke Telegram and Discord replies for MiniMax-backed sessions.

Root Cause

Hermes routes MiniMax through anthropic_messages mode, but build_anthropic_client() inferred auth mode only from Anthropic token shape:

• native Anthropic API keys -> x-api-key
• everything else -> Anthropic OAuth/setup-token bearer flow

MiniMax is Anthropic-compatible at the message API layer, but not at the auth layer. Its /anthropic endpoints expect regular API keys via Authorization: Bearer ..., not Anthropic's native x-api-key header.

Because MiniMax secrets do not use Anthropic's sk-ant-api prefix, Hermes could also misclassify them as Anthropic OAuth/setup tokens and attach Claude Code OAuth headers that do not belong on MiniMax requests.

Fix

• add _requires_bearer_auth() to detect Anthropic-compatible providers that require bearer auth
• force MiniMax global and China /anthropic endpoints through auth_token instead of api_key
• keep native Anthropic auth behavior unchanged
• check provider-specific bearer handling before Anthropic OAuth token-shape detection
• add a regression test covering MiniMax's Anthropic endpoint auth path

Testing

• uv run --with pytest --with pytest-xdist python -m pytest tests/test_anthropic_adapter.py tests/test_run_agent.py -q -k 'anthropic or minimax'
  • 118 passed

Research Notes

Checked the adjacent ecosystem before patching:

• MiniMax's docs show Authorization: Bearer <key> for ChatCompletion v2 requests
• bkerf/claude-code-multi configures MiniMax with auth_token
• MiniMax-AI/Mini-Agent explicitly sets Authorization: Bearer {api_key} even when using Anthropic's SDK
• OpenClaw has matching bug reports for MiniMax Anthropic-mode 401s caused by incorrect auth-header behavior

[teknium1]

Merged via #4028 onto current main. Cherry-picked with authorship preserved. Fixed 3 test values that had display-tool redaction artifacts. MiniMax Anthropic endpoints now correctly use Bearer auth. Thanks @kshitijk4poor!