fix: apply mergeToolResultText only for Mistral family models in OpenAI provider

[roomote]

Related GitHub Issue

Closes: #10684

Related: #10618, #10540, #10695 (same root cause, different providers/approaches)

Description

This PR attempts to address Issue #10684 based on feedback from @maksir suggesting we should check the model family before applying the mergeToolResultText fix to avoid affecting other models.

Changes:

• Added isMistralFamily check that detects Mistral/Devstral models by checking if the model ID contains "mistral" or "devstral" (case-insensitive)
• Pass { mergeToolResultText: true } to convertToOpenAiMessages() only when isMistralFamily is true
• Updated all 4 convertToOpenAiMessages() calls in the OpenAI provider (both streaming and non-streaming modes, including O3 family handlers)

This follows the same pattern as PR #10630 which implements the model family check for OpenRouter.

Root Cause:
Mistral/Devstral models enforce strict message ordering and reject a "user" role message immediately after a "tool" role message. The mergeToolResultText option merges text content into the last tool message instead of creating a separate user message.

Test Procedure

1. Configure OpenAI provider with a local vLLM/llama.cpp/Ollama server serving a Mistral/Devstral model
2. Start a task that uses tools
3. Verify that tool calls complete without the "Unexpected role user after role tool" error
4. Test with non-Mistral models to verify normal behavior is preserved

Pre-Submission Checklist

• Issue Linked: This PR is linked to an approved GitHub Issue (see "Related GitHub Issue" above).
• Scope: My changes are focused on the linked issue (one major feature/fix per PR).
• Self-Review: I have performed a thorough self-review of my code.
• Testing: All existing tests pass. The underlying mergeToolResultText functionality is tested in openai-format.spec.ts.
• Documentation Impact: I have considered if my changes require documentation updates (see "Documentation Updates" section below).
• Contribution Guidelines: I have read and agree to the Contributor Guidelines.

Documentation Updates

• No documentation updates are required.

Additional Notes

This approach is more conservative than PR #10695 which applies mergeToolResultText: true to all models. By checking the model family first, we avoid any potential side effects on models that do not require this fix.

Feedback and guidance are welcome!

---

Important

Adds isMistralFamily check in OpenAiHandler to conditionally apply mergeToolResultText for Mistral/Devstral models, ensuring correct message ordering.

• Behavior:
  • Adds isMistralFamily check in OpenAiHandler to identify Mistral/Devstral models by checking modelId for "mistral" or "devstral".
  • Applies { mergeToolResultText: true } in convertToOpenAiMessages() only if isMistralFamily is true.
  • Updates all 4 convertToOpenAiMessages() calls in OpenAiHandler for both streaming and non-streaming modes.
• Root Cause:
  • Mistral/Devstral models require strict message ordering, rejecting a "user" role message immediately after a "tool" role message.
• Testing:
  • Ensure no "Unexpected role user after role tool" error with Mistral/Devstral models.
  • Verify normal behavior with non-Mistral models.

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Rooviewer   See task on Roo Cloud

Review complete. No issues found.

The implementation correctly adds isMistralFamily detection and conditionally applies mergeToolResultText: true for Mistral/Devstral models, which prevents the "Unexpected role 'user' after role 'tool'" error. The fix is applied to all 4 convertToOpenAiMessages() calls and follows the established pattern from other providers.

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