[bot] Add instrumentation for Mistral AI Go SDK (`mistralai/client-go`)

[braintrust-bot]

Summary

The Braintrust Go SDK instruments OpenAI, Anthropic, Google GenAI, sashabaranov/go-openai, LangChainGo, Firebase Genkit, Google ADK, CloudWeGo Eino, and AWS Bedrock — but does not instrument the Mistral AI Go SDK (github.com/mistralai/client-go). Mistral is explicitly listed as a supported provider in Braintrust's tracing documentation, yet it has no SDK-level instrumentation wrapper in this repository.

What is missing

A trace/contrib/mistral/ integration module that wraps execution calls on the Mistral AI Go client. The key execution surfaces are:

• Chat / ChatStream — conversational model inference (non-streaming and streaming), including multi-turn conversations and tool calling
• Embed — vector embedding generation

The Mistral Go SDK is generated with the Stainless SDK toolchain (same as openai-go and anthropic-sdk-go), and exposes option.WithMiddleware() for HTTP middleware injection, making it directly instrumentable with the same internal.Middleware(router, logger) pattern already used by the existing OpenAI and Anthropic integrations.

Braintrust docs status

supported — Braintrust explicitly lists Mistral as a supported provider for tracing:

"OpenAI, Anthropic, Gemini, AWS Bedrock, Azure, Mistral, Together, Groq, and many more"

Source: https://www.braintrust.dev/docs/guides/tracing and https://www.braintrust.dev/docs/instrument

However, there is no Go SDK-level tracing wrapper for the Mistral AI client in this repository.

Upstream sources

• Mistral AI Go SDK repository: https://github.com/mistralai/client-go
• Mistral AI Go SDK on pkg.go.dev: https://pkg.go.dev/github.com/mistralai/client-go
• Mistral API reference: https://docs.mistral.ai/api/
• Mistral AI SDK documentation: https://docs.mistral.ai/

Braintrust docs sources

• https://www.braintrust.dev/docs/guides/tracing (lists Mistral as supported provider)
• https://www.braintrust.dev/docs/instrument (lists Mistral as supported provider)

Local repo files inspected

• go.mod — no mistralai/client-go dependency
• trace/contrib/ — no mistral/ directory exists
• trace/contrib/all/all.go — no Mistral import
• examples/internal/ — no Mistral example
• Grep for mistral across all repo files — zero matches
• trace/contrib/openai/traceopenai.go — reference pattern: internal.Middleware(router, logger) with option.WithMiddleware() injection; same pattern applies to client-go since both are Stainless-generated SDKs
• trace/contrib/anthropic/traceanthropic.go — reference pattern for Stainless-generated SDK middleware instrumentation