fix: handle empty tools list in OpenAILegacy provider

[li-xiu-qi]

Some OpenAI-compatible APIs (like DashScope/Aliyun) reject requests with empty tools list.

This fix only includes the 'tools' parameter when tools are actually present.

Related Issue

N/A - This is a minor bug fix (15 lines of code) that addresses an API compatibility issue.

Description

Problem

When kosong.step() is called with EmptyToolset() (e.g., during context compaction), the OpenAILegacy provider sends an empty tools list to the API. Some OpenAI-compatible APIs (like DashScope/Aliyun) strictly validate the request and reject empty tools lists with error:

Error code: 400 - {'error': {'message': "[] is too short - 'tools'", 'type': 'invalid_request_error'}}

This prevents context compaction from working when using these APIs.

Solution

Modified OpenAILegacy.generate() to only include the tools parameter in the API request when tools are actually present (non-empty). The fix builds request kwargs dynamically:

• Always include: model, messages, stream, generation kwargs
• Conditionally include: tools (only if non-empty), stream_options (only if streaming), reasoning_effort (only if set)

Changes

• packages/kosong/src/kosong/contrib/chat_provider/openai_legacy.py: Modified generate() method to conditionally include tools parameter

Testing

• Tested with DashScope API (deepseek-v3 model)
• Context compaction now works without errors
• Normal tool calls continue to work as expected
• Empty tools list no longer triggers API error

Checklist

• I have read the CONTRIBUTING document.
• I have linked the related issue, if any. (N/A - no existing issue for this specific bug)
• I have added tests that prove my fix is effective or that my feature works. (Minor fix, existing tests cover the functionality)
• I have run make gen-changelog to update the changelog.
• I have run make gen-docs to update the user documentation.

Notes for Reviewers

This is a minimal, backward-compatible fix that only affects request building logic in the OpenAILegacy provider. The change ensures compatibility with stricter OpenAI-compatible APIs while maintaining existing behavior for all other use cases.

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[devin-ai-integration]

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