[BUG] Mistral: duplex option is required

[MSaltersFF]

Problem (one or two sentences)

Using Mistral condestral-latest stopped working, with error message "API Request Failed".

Context (who is affected and when)

Affects all use of codestral - core API broken

Reproduction steps

VS Code 1.113 on Mac OSX Tahoe 26.4
Roo Code 3.51.1
Mistral codestral-latest
Ask Roo Code to "review code" (or any other prompt)

Expected result

Prompt sent to Mistral and handled

Actual result

Mistral completion error: Unexpected HTTP client error: TypeError: RequestInit: duplex option is required when sending a body.

Variations tried (optional)

Mode switched.

App Version

3.51.1

API Provider (optional)

Mistral AI

Model Used (optional)

codestral-latest

Roo Code Task Links (optional)

No response

Relevant logs or errors (optional)

Mistral completion error: Unexpected HTTP client error: TypeError: RequestInit: duplex option is required when sending a body.

Google suggests this is a common issue with some Node.js versions: https://github.com/nodejs/node/issues/46221

[roomote-v0]

I've analyzed this issue and here's my proposed implementation plan:

Root Cause: The @mistralai/mistralai SDK (v1.9.18) uses the native fetch() API internally via its HTTPClient class. In newer versions of Node.js (18+), the Fetch API requires duplex: "half" in RequestInit when the request includes a body. The SDK's default fetcher does not set this option, causing the error: TypeError: RequestInit: duplex option is required when sending a body.

Proposed Fix:

1. In src/api/providers/mistral.ts, import the HTTPClient class from @mistralai/mistralai/lib/http.js
2. When constructing the Mistral client (line 67-72), provide a custom httpClient that wraps the native fetch() and always includes duplex: "half" in the request init:

import { HTTPClient } from "@mistralai/mistralai/lib/http.js"

// In the constructor:
const httpClient = new HTTPClient({
    fetcher: (input, init) => {
        return fetch(input, { ...init, duplex: "half" } as RequestInit);
    },
});

this.client = new Mistral({
    serverURL: ...,
    apiKey: ...,
    httpClient,
});

This is safe because duplex: "half" is harmlessly ignored when there is no request body. The SDK explicitly supports this customization via its httpClient constructor option.

3. Update the existing test file src/api/providers/__tests__/mistral.spec.ts to verify the custom HTTP client is passed through.

Why not just upgrade the SDK? The latest v1.15.1 still uses the same Speakeasy-generated HTTPClient with the same default fetcher, so upgrading alone would not fix the issue. The custom fetcher approach is the correct solution.

Please mention @roomote in a comment saying that you approve this plan, and I'll proceed with the implementation.