fix: ensure correct precedence for roleDefinition and customInstructions when generating system prompt

[ChuKhaLi]

Related GitHub Issue

Closes: #2558

Description

• modify the logic get roleDefinition and baseInstructions in get system prompt on system.ts file
• the logic follow PromptsView.tsx, as custom mode's instruction > user prompt > built-in

Test Procedure

Type of Change

• 🐛 Bug Fix: Non-breaking change that fixes an issue.
• ✨ New Feature: Non-breaking change that adds functionality.
• 💥 Breaking Change: Fix or feature that would cause existing functionality to not work as expected.
• ♻️ Refactor: Code change that neither fixes a bug nor adds a feature.
• 💅 Style: Changes that do not affect the meaning of the code (white-space, formatting, etc.).
• 📚 Documentation: Updates to documentation files.
• ⚙️ Build/CI: Changes to the build process or CI configuration.
• 🧹 Chore: Other changes that don't modify src or test files.

Pre-Submission Checklist

• Issue Linked: This PR is linked to an approved GitHub Issue (see "Related GitHub Issue" above).
• Scope: My changes are focused on the linked issue (one major feature/fix per PR).
• Self-Review: I have performed a thorough self-review of my code.
• Code Quality:
  • My code adheres to the project's style guidelines.
  • There are no new linting errors or warnings (npm run lint).
  • All debug code (e.g., console.log) has been removed.
• Testing:
  • New and/or updated tests have been added to cover my changes.
  • All tests pass locally (npm test).
  • The application builds successfully with my changes.
• Branch Hygiene: My branch is up-to-date (rebased) with the main branch.
• Documentation Impact: I have considered if my changes require documentation updates (see "Documentation Updates" section below).
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Documentation Updates

Does this PR necessitate updates to user-facing documentation?

• No documentation updates are required.

Additional Notes

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Important

Fixes prompt generation precedence by introducing getModeSelection to prioritize custom instructions and role definitions.

• Behavior:
  • Updates generatePrompt and SYSTEM_PROMPT in system.ts to use getModeSelection for determining roleDefinition and baseInstructions.
  • Ensures precedence: custom mode's instruction > user prompt > built-in.
• Functions:
  • Adds getModeSelection in modes.ts to encapsulate logic for selecting roleDefinition and baseInstructions.
• Tests:
  • Adds tests for getModeSelection in modes.test.ts to verify correct precedence handling and fallback behavior.

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[daniel-lxs]

Hey @ChuKhaLi, this looks good to me, can we solve the merge conflicts?

[ChuKhaLi]

Hey @ChuKhaLi, this looks good to me, can we solve the conflict issues?

done, pls have a look

[daniel-lxs]

Thank you! LGTM

Makes sense to be consistent and actually use the role definitions and instructions present in the custom mode files when the file exists.