Console Go: Anthropic-route tool calls fail with 400 'function name is invalid' for Kimi models (kimi-k3, kimi-k2.7-code)

Summary

Requests to https://opencode.ai/zen/go/v1/messages (Anthropic route) with any tool that carries an input_schema fail with HTTP 400 for the Kimi models (kimi-k3, kimi-k2.7-code). Other models on the same route accept the identical request.

Error

400 invalid_request_error
"Error from provider (Console Go): Upstream request failed: [invalid_request_error] Invalid request: function name is invalid, must start with a letter and can contain letters, numbers, underscores, and dashes"

The error is misleading: the tool names are all valid (Bash, Edit, mcp__codegraph__codegraph_explore, ...). Bisection shows the trigger is the presence of the input_schema key, not its content and not the name.

Reproduction

1. Build an Anthropic /v1/messages request with model: "kimi-k3" and any single tool, e.g.:

   {"name": "Bash", "description": "run", "input_schema": {"type": "object", "properties": {"command": {"type": "string"}}}}
   

2. POST to https://opencode.ai/zen/go/v1/messages with an opencode-go key.
3. Result: 400 with the error above.

Bisection results (same body, only the tool definition varied, model kimi-k3):

Additional data

• The OpenAI route works for the same models: POST /v1/chat/completions with tools: [{type: "function", ...}] on kimi-k3 succeeds. So this is specific to the Anthropic-route tool-schema conversion for the Kimi upstream.
• Affects every Claude Code session pointed at ANTHROPIC_BASE_URL=https://opencode.ai/zen/go with a Kimi model — the very first request fails because Claude Code always sends tool schemas.
• Workaround today: use a non-Kimi model (qwen3.8-max, minimax-m3, deepseek-v4-flash, gpt-5.6-luna) on the Anthropic route. Claude Code's native OpenAI env route is not an alternative in v2.1.220 (it rejects models not in its own list).

Environment

• Gateway: opencode.ai/zen/go ("Console Go" provider)
• Client: Claude Code 2.1.220, also plain HTTP replay against the gateway (no client involved)
• Date: 2026-08-07

No repository file or test path is named; start by tracing the Anthropic /v1/messages entry point and the tool-schema conversion for the Console Go provider. Reproduce the Kimi request with an input_schema, compare it with the working OpenAI route and other models, and consider the issue done when valid tool schemas are accepted by kimi-k3 and kimi-k2.7-code without breaking other Anthropic-route models.