feat(js/plugins/compat-oai): Add reasoning_content and json_schema support to OpenAI Compatible API plugin

[neokn]

This commit adds comprehensive support for handling reasoning_content in OpenAI Compatible API Chat Completions responses, supporting both streaming and non-streaming scenarios. The implementation ensures that models supporting reasoning_content can properly return their reasoning traces, with optimized content assembly and enhanced response_format handling.

CHANGELOG:

• Add reasoning_content handling in fromOpenAIChoice and fromOpenAIChunkChoice
• Implement direct content assembly by pushing reasoning and content parts to content array
• Update response_format handling in toOpenAIRequestBody to support schema-based responses
• Add comprehensive test cases for reasoning_content in both streaming and non-streaming functions
• Add test for json_schema response_format in toOpenAIRequestBody

Description here... Help the reviewer by:
OpenAI it self not support reasoning_content but

• xAI
• DeepSeek
• LiteLLM

support reasoning_content when using reasoning model

Checklist (if applicable):

• PR title is following https://www.conventionalcommits.org/en/v1.0.0/
• Tested (manually, unit tested, etc.)
• Docs updated (updated docs or a docs bug required)

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[neokn]

Hi @pavelgj, just wanted to kindly check if you’ve had a chance to look at this PR.
Please let me know if there’s anything I can update or clarify. Thanks a lot!

[pavelgj]

@ssbushi could you please take a look?

[ssbushi]

Thanks for the PR. Looks good overall, I just need a bit of clarification on the json schema change. :)

[ssbushi]

I could not find API reference for json_schema for DeepSeek. Are you sure this works?

http://api-docs.deepseek.com/api/create-chat-completion#request

[neokn]

hi @ssbushi thanks for your review, yes, DeepSeek didn't support json_schema
so there still has fallback for json_object
when integrate to DeepSeek, user can set the output.format without JsonSchema
e.g. ai.generate({output: {format: 'json'}});

then it will fallback to

body.response_format = {
    type: 'json_object',
};

I'm follow these two document for implement json_schema part
LiteLLM
OpenAI
xAI