Go API endpoint fails tool-calling validation in Positron Assistant #28652

Description

Go API endpoint fails tool-calling validation in Positron Assistant

Context

I am a paying Go subscriber trying to use the Go API endpoint (https://opencode.ai/zen/go/v1) with Positron Assistant (a data science IDE by Posit). Positron supports custom OpenAI-compatible providers, but the Go endpoint fails its Sign in validation every time.

Evidence that the endpoint works normally

Basic requests work fine:

# Models endpoint
curl https://opencode.ai/zen/go/v1/models \
  -H "Authorization: Bearer <API_KEY>"
# Returns valid model list

# Chat completions
curl https://opencode.ai/zen/go/v1/chat/completions \
  -H "Authorization: Bearer <API_KEY>" \
  -H "Content-Type: application/json" \
  -d '{"model": "kimi-k2.5", "messages": [{"role": "user", "content": "hi"}], "max_tokens": 10}'
# Returns valid completion

The suspected issue

Positron validates providers by sending a request with a tools parameter during Sign in, to confirm tool-calling support. Based on my investigation, the Go endpoint likely returns a response that doesn't match what Positron expects for this specific request format, causing the validation to fail.

Could you test the following and confirm whether it works correctly on your end:

curl https://opencode.ai/zen/go/v1/chat/completions \
  -H "Authorization: Bearer <API_KEY>" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "kimi-k2.5",
    "messages": [{"role": "user", "content": "hi"}],
    "tools": [{"type": "function", "function": {"name": "test", "description": "test", "parameters": {"type": "object", "properties": {}}}}],
    "max_tokens": 10
  }'

Impact

I paid for a Go subscription specifically to use these models in my IDE. Right now the only workaround is running a local litellm proxy, which is unreasonable for what should be a simple API integration.

Positron is actively growing its user base among data scientists. Better compatibility with the Go endpoint would benefit both communities. Would appreciate any guidance or fix on the Go side.

Plugins

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OpenCode version

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Steps to reproduce

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Screenshot and/or share link

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Operating System

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Terminal

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