fix(chatopenai): support stop in base options

[Javi-vahe]

Summary

• Support stop when provided through ChatOpenAI Base Options.
• Extract stop from parsed base options and apply it to the model options instead of sending it as a default header.
• Preserve the existing Stop Sequence field behavior by only using Base Options stop when obj.stop is not already set.

Fixes #2499

Tests

• git diff --check

[gemini-code-assist]

Code Review

This pull request adds support for parsing and applying the stop parameter from parsedBaseOptions in the ChatOpenAI component. The reviewer identified two critical issues: potential compatibility problems with reasoning models (which do not support stop sequences) and unexpected side effects from mutating the original input object. A code suggestion was provided to resolve both issues.

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[gemini-code-assist]

There are two issues with this implementation:

1. Reasoning Models Compatibility: OpenAI's reasoning models (e.g., o1 series) do not support stop sequences, which is why obj.stop is explicitly deleted on lines 266-268. However, because this new block runs after that check, any stop sequence provided in baseOptions will still be assigned to obj.stop, potentially causing API errors. We should ensure stop is not set for reasoning models.
2. Input Object Mutation: If baseOptions is passed as an object, parsedBaseOptions holds a direct reference to it. Mutating it with delete parsedBaseOptions.stop will modify the original nodeData.inputs.baseOptions object, which can cause unexpected side effects if the node is re-initialized or reused. We should shallow copy the object before deleting the property.

Here is the suggested fix to address both issues:

        if (parsedBaseOptions?.stop) {
            const stop = parsedBaseOptions.stop

            if (!obj.stop && !isReasoningModelOpenAI(modelName)) {
                obj.stop = Array.isArray(stop)
                    ? stop.map((item) => String(item).trim()).filter(Boolean)
                    : String(stop)
                          .split(',')
                          .map((item) => item.trim())
                          .filter(Boolean)
            }

            if (typeof baseOptions === 'object') {
                parsedBaseOptions = { ...parsedBaseOptions }
            }
            delete parsedBaseOptions.stop

            if (Object.keys(parsedBaseOptions).length === 0) {
                parsedBaseOptions = undefined
            }
        }

[Javi-vahe]

Hi maintainers, I opened this PR to address #2499.

The issue happens because Base Options are currently parsed into the OpenAI configuration/default headers path, so a stop value provided there does not reach the model invocation options. This PR extracts stop from parsed Base Options and applies it to obj.stop, while preserving the existing Stop Sequence field behavior.

Please let me know if you'd prefer a different approach.