Feature: Custom Instructions for GitLab Duo Chat

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This feature idea has emerged independently from multiple directions, indicating strong user demand:

• #500822 : Request for reusable prompt templates to improve workflow efficiency
• #497807: Request for custom instructions to support language preferences and specialized outputs

While those issues proposed different solutions (templates system, suffix features), they point to the same core need: users want persistent, reusable ways to frame their Duo Chat interactions. This proposal aims to solve that core need with a simple first iteration that can be expanded based on usage and feedback.

Business Results:

• Strong customer traction:
  • Users need reusable contexts for specialized workflows #500822
  • Already being used by customers through manual copy/paste #497807 (comment 2254673319)
• Immediate business value:
  • Unlock enterprise adoption blockers #497807 (comment 2209424948)
  • Improve workflow efficiency #497807 (comment 2254673319)
  • Reduce repetitive context setting
• Industry standard:
  • Matches features in competitors
  • Expected in enterprise AI tools

Proposed Solution

Add a "Custom Instructions" section to Duo Chat:

1. Single Custom Instructions Field

• Text area for custom instructions/context
• Prepended only to first message in each thread
• Character limit (e.g. 500 chars)
• Applied globally per user

This minimal approach:

• Solves the core need for persistent context
• Uses proven prepend approach
• Requires minimal UI changes
• Can be built on existing preferences infrastructure
• Provides foundation for future template system

User Experience

1. Settings UI:

• Add "Duo Chat" section to user preferences
• Large text area with character counter
• Save button that shows success/error feedback
• Placeholder text: "Add instructions that will be prepended to your first message in each chat thread"

2. Chat Flow:

• New thread starts -> Custom instructions prepended silently
• No visual indicator in chat that instructions were added
• If token limit exceeded -> Show error: "Your message plus custom instructions exceed the token limit. Please shorten your message or reduce custom instructions."

3. Default States:

• Empty text area by default
• Empty string if no instructions set
• Preserved across sessions

Success Metrics

• Custom instruction usage rate
• User feedback on workflow improvements

Future Iterations

• Multiple named instruction templates
• Per-thread instruction switching
• Shareable templates

Acceptance Criteria

• User can save custom instructions via preferences
• Instructions persist across sessions
• Instructions are prepended to first message in new threads
• Character limit is enforced with UI feedback
• Token limit errors are handled gracefully
• Instructions are cleared when preferences are reset