feat(xai): Correctly report tool-calls finish reason for xAI models

[subhraneel2005]

Background

This change was necessary because xAI models, particularly grok-4.1-fast-reasoning, were incorrectly reporting a finishReason of "stop" when they had, in fact, performed tool calls. This led to an inconsistent FinishReason being reported by the AI SDK, leading to potential inconsistencies in how tool-calling completions were handled. The xAI API documentation indicates that tool calls are primarily signaled by the presence of tool_call objects in the response, rather than a distinct finish_reason string, and a general "stop" reason could be returned even with an active tool call.

Summary

This pull request modifies the xAI provider within the AI SDK (packages/xai/src/xai-chat-language-model.ts). The changes introduce logic to explicitly detect the presence of tool_call objects in the xAI model's response (for both doGenerate and doStream methods). If tool calls are identified, the finishReason is now overridden and set to 'tool-calls'. This ensures that the AI SDK consistently and accurately reports the FinishReason as 'tool-calls' whenever an xAI model invokes a tool, regardless of the raw finish_reason string provided by the xAI API.

Manual Verification

The fix was verified by running the comprehensive test suite for the packages/xai package. All 154 tests passed across both Node.js and Edge environments, indicating that the changes correctly address the finishReason issue without introducing regressions or breaking existing functionality.

Checklist

• Tests have been added / updated (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)
• A patch changeset for relevant packages has been added (for bug fixes / features - run pnpm changeset in the project root)
• I have reviewed this pull request (self-review)

Related Issues

[aayush-kapoor]

this will not work - the incorrect reason is being passed through AI Gateway and it's not on the xai provider

[subhraneel2005]

okayy