bug(MimoHandler): Type safety gaps and unhandled stream abort scenarios

[proyectoauraorg]

Description

The MimoHandler.createMessage() method in src/api/providers/mimo.ts has several type safety issues and missing edge-case handling that could lead to runtime errors or silent failures in production.

Current Behavior

1. any[] parameter type for messages

// src/api/providers/mimo.ts:70
override async *createMessage(
    systemPrompt: string,
    messages: any[],  // Should be Anthropic.Messages.MessageParam[]
    metadata?: ApiHandlerCreateMessageMetadata,
): ApiStream {

The parent OpenAiHandler uses Anthropic.Messages.MessageParam[] for the messages parameter. The override in MimoHandler widens this to any[], losing compile-time safety.

2. Multiple as any casts hiding potential issues

// Line 102 — double cast
stream = (await this.client.chat.completions.create(params as any)) as any

// Line 147 — unsafe access to prompt_tokens_details
const cacheWriteTokens = (lastUsage?.prompt_tokens_details as any)?.cache_write_tokens || 0

The double as any on the API call bypasses the OpenAI SDK type checking entirely. If MiMo's API changes its response shape, TypeScript will not catch it.

3. No AbortController / stream cancellation handling

The createMessage method streams via for await (const chunk of stream) but has no mechanism to:

• Cancel an in-flight request when the user aborts
• Handle AbortError if the underlying fetch is cancelled
• Clean up resources on early termination

Other handlers like OpenAiNativeHandler and AnthropicHandler use an AbortController and handle cancellation signals.

Proposed Fix

override async *createMessage(
    systemPrompt: string,
    messages: Anthropic.Messages.MessageParam[],  // proper type
    metadata?: ApiHandlerCreateMessageMetadata,
): ApiStream {
    // ...
    const controller = new AbortController()
    
    try {
        stream = await this.client.chat.completions.create(
            params as OpenAI.Chat.Completions.ChatCompletionCreateParamsStreaming,
            { signal: controller.signal }
        )
    } catch (error) {
        if ((error as Error).name === "AbortError") return
        throw handleProviderError(error, "MiMo")
    }
    // ...
}

Impact

• Severity: Medium — Works today but is fragile to API changes
• Scope: src/api/providers/mimo.ts only
• Risk of fix: Low — tightening types is non-breaking

Additional Context

The mimo-v2-flash model is explicitly excluded from mimoModels in packages/types/src/providers/mimo.ts due to reasoning_content passthrough issues. A well-typed handler would make it easier to validate and add flash support in the future.

[proyectoauraorg]

Auto-assigned for implementation. Will create a fix PR addressing: (1) type-safe messages parameter, (2) replace double as any casts, (3) add AbortController for stream cancellation. ETA: 2026-06-05.