Summary

Xiaomi MiMo's Anthropic-compatible /anthropic endpoint requires reasoning_content on every assistant message when thinking mode is enabled. Omitting it causes HTTP 400:

The reasoning_content in the thinking mode must be passed back to the API.

This PR adds three fixes:

1. run_agent.py — Xiaomi reasoning pad detection

Added _needs_xiaomi_tool_reasoning() matching provider xiaomi/mimo/xiaomi-mimo or base_url containing xiaomimimo.com. Included in _needs_thinking_reasoning_pad() so the padding logic applies to MiMo tool-call replays (same pattern as DeepSeek #15250 and Kimi #17400).

2. agent/anthropic_adapter.py — Anthropic adapter compatibility

• Added _is_xiaomi_anthropic_endpoint() function
• Added it to _preserve_unsigned_thinking whitelist so unsigned thinking blocks survive signature stripping on third-party endpoints
• Fixed reasoning_content → thinking block insertion to always insert even when _already_has_thinking is True, because signed blocks from reasoning_details will be stripped by the third-party endpoint code below

3. gateway/run.py — Prevent infinite retry loop

Added is_reasoning_echo_failure detection matching "reasoning_content", "thinking mode", "must be passed back" in error messages. When triggered:

• Auto-resets the session (like compression_exhausted)
• Skips transcript persistence (don't grow a broken session)
• Logs a warning instead of "Transient agent failure"

Without this, the gateway enters an infinite retry loop on the same stale session history that always produces the same 400 error. Observed: a session retried for 2+ hours hitting the same error every time.

Testing

# Verify Xiaomi detection
hermes chat -q "echo hello" -m mimo-v2.5-pro --provider xiaomi --yolo

# Verify gateway doesn't infinite retry on stale sessions
# (requires a session that previously hit the reasoning_content 400)

Related

• Refs [Bug]: DeepSeek V4 Flash Discord session poisoned when tool-call assistant lacks reasoning_content #15250 (DeepSeek reasoning_content)
• Refs reasoning_content dropped in multi-turn tool calls with DeepSeek v4 (causes HTTP 400) #17400 (Kimi reasoning_content)
• Refs #mimo-pass-back (Xiaomi MiMo)