fix: have frontend populate "stop" field in OpenAI request

[furionw]

Overview:

Documented in #4755

When frontend receives an OpenAI request,

• it does deserialize it correctly so that NvCreateCompletionRequest.inner.stop has it
• it doesn't implement get_stop

because of this, the Preprocessor is not able to build the request with proper stop field. Therefore the backend cannot honor the OpenAI request stop.

This PR fixes that.

Details:

Update get_stop function to return the values for the (backend) request builder.

Testing

• added unit test
• test locally by running frontend and engine

Summary by CodeRabbit

• Bug Fixes

  • Enhanced stop sequence handling in completion requests to properly process and return configured stop values.

• Tests

  • Added unit tests for stop sequence handling scenarios, including single, multiple, and no stop configurations.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

Walkthrough

The get_stop method in NvCreateCompletionRequest is now implemented to properly map Stop enum variants (String and StringArray) to a Vec output. Previously, it unconditionally returned None. Unit tests validate the mapping across three scenarios: absent stop, single stop value, and multiple stop values.

Changes

Cohort / File(s)	Summary
Stop field mapping implementation lib/llm/src/protocols/openai/completions.rs	Implemented get_stop to handle Stop::String and Stop::StringArray enum variants, converting them to Vec. Added three unit tests: test_get_stop_none, test_get_stop_single, and test_get_stop_multiple.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

• Straightforward enum-to-Vec mapping logic with no complex branching or state management
• Basic unit tests with clear, predictable assertions
• Single file modification with cohesive changes

Poem

🐰 A stop field once silent and still,
Now speaks with a voice and a will—
One word or many, the enum does parse,
Into strings within vectors so sparse,
With tests that ensure all is well! ✨

Pre-merge checks

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 40.00% which is insufficient. The required threshold is 80.00%.	You can run @coderabbitai generate docstrings to improve docstring coverage.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: enabling the frontend to populate the 'stop' field in OpenAI requests, which aligns with the get_stop implementation fix in the changeset.
Description check	✅ Passed	The pull request description follows the template structure with Overview, Details, and Testing sections clearly addressing the fix for the missing stop field implementation.

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[furionw]

creating #4782 to see if I can pass the test ...