Strict Anthropic-compatible gateways (e.g. MiniMax) reject Claude-format
requests with HTTP 400 when tools[].type is missing. Normalize each
missing/falsy tools[].type to "custom" before dispatch when the final
request format is Claude. Built-in tool types (computer_use, bash,
web_search_*) are passed through untouched.
flattenToolHistory only recognized OpenAI-style tool calls. Anthropic-compatible clients (Claude Code, /v1/messages) send tool invocations and results as tool_use/tool_result blocks inside the message content array. Since panel calls strip the tools definitions (#1859), the panel expert models received structured tool history without schemas, causing them to fail or misbehave (leading to empty responses and 503 errors).
Extend flattenToolHistory to recognize and flatten tool_use and tool_result blocks in the content array into prose text, keeping panel expert execution robust and independent of the client API format.
PR decolua/9router#1910
Co-authored-by: Cursor <cursoragent@cursor.com>
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