Fix: protect instruction insertion from being placed directly before function call

[UlookEE]

…a function call.

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Link to Issue or Description of Change

1. Link to an existing issue (if applicable):
Fix #3229

• Closes: #issue_number
• Related: #issue_number

Testing Plan

_Please describe the tests that you ran to verify your changes. This is required
for all PRs that are not small documentation or typo fixes.

Make unit tests, test complete

Unit Tests:

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• All unit tests pass locally.

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Manual End-to-End (E2E) Tests:

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necessary setup or configuration. Please provide logs or screenshots to help
reviewers better understand the fix.

Checklist

• I have read the CONTRIBUTING.md document.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• I have manually tested my changes end-to-end.
• Any dependent changes have been merged and published in downstream modules.

Additional context

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[gemini-code-assist]

Summary of Changes

Hello @UlookEE, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves an issue where system instructions could be inadvertently inserted into an LLM request at an invalid position, specifically immediately preceding user messages or function call interactions. The changes introduce a robust validation mechanism to ensure instructions are always placed in appropriate locations within the content sequence, thereby preserving the intended conversational structure and tool execution order.

Highlights

• Instruction Insertion Logic Refinement: The logic for inserting instructions into LLM request contents has been updated to prevent them from being placed directly before user content or function calls, ensuring a more coherent conversation flow.
• New Helper Function: A new private helper function, _is_valid_instruction_position, was introduced to determine appropriate insertion points for instructions, checking for user roles and function call parts.
• Enhanced Test Coverage: New unit tests have been added to specifically verify that instructions are correctly skipped when encountering function call content or leading user content, confirming the fix's effectiveness.

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[gemini-code-assist]

Code Review

This pull request correctly addresses the issue of preventing instruction insertion directly before a function call. The logic has been refactored into a new helper function, _is_valid_instruction_position, which improves code clarity. The accompanying unit tests are thorough and validate the new behavior effectively. I have one suggestion to make the implementation of the new helper function more concise.