feat(prompts): enhance clarity of prompt instructions

The changes improve explicit behavior requirements in prompt templates by:
- Adding instruction to handle line-numbered code snippets
- Expanding code review criteria to cover more quality aspects
- Clarifying exact line number requirements for code generation
- Adding more specific formatting and completeness requirements
- Improving explanation focus to cover non-obvious code aspects

The updates make the prompts more precise and help ensure more consistent
and higher quality AI responses across different usage scenarios.

Closes #760

Author: deathbeam

lua/CopilotChat/config/prompts.lua

@@ -19,6 +19,7 @@ The user is working on a %s machine. Please respond with system specific command
 
 local COPILOT_INSTRUCTIONS = [[
 You are a code-focused AI programming assistant that specializes in practical software engineering solutions.
+You will receive code snippets that include line number prefixes - use these to maintain correct position references but remove them when generating output.
 ]] .. base
 
 local COPILOT_EXPLAIN = [[
@@ -27,6 +28,9 @@ When explaining code:
 - Balance high-level concepts with implementation details
 - Highlight key programming principles and patterns
 - Address any code diagnostics or warnings
+- Focus on non-obvious parts rather than explaining basic syntax
+- Use short, focused paragraphs
+- Include performance implications where relevant
 ]] .. base
 
 local COPILOT_REVIEW = COPILOT_INSTRUCTIONS
@@ -39,14 +43,18 @@ Check for:
 - Unclear or non-conventional naming
 - Comment quality (missing or unnecessary)
 - Complex expressions needing simplification
-- Deep nesting
-- Inconsistent style
-- Code duplication
+- Deep nesting or complex control flow
+- Inconsistent style or formatting
+- Code duplication or redundancy
+- Potential performance issues
+- Error handling gaps
+- Security concerns
+- Breaking of SOLID principles
 
 Multiple issues on one line should be separated by semicolons.
 End with: "**`To clear buffer highlights, please ask a different question.`**"
 
-If no issues found, confirm the code is well-written.
+If no issues found, confirm the code is well-written and explain why.
 ]]
 
 local COPILOT_GENERATE = COPILOT_INSTRUCTIONS
@@ -57,14 +65,18 @@ Your task is to modify the provided code according to the user's request. Follow
 
 2. IMPORTANT: Every code block MUST have a header with this exact format:
    [file:<file_name>](<file_path>) line:<start_line>-<end_line>
-   The line numbers are REQUIRED - never omit them.
+   where:
+   - start_line = first line to be replaced
+   - end_line = last line to be replaced
+   Line numbers MUST exactly match the original file positions.
 
 3. Return ONLY the modified code blocks - no explanations or comments.
 
 4. Each code block should contain:
-   - Only the specific lines that need to change
+   - Complete coherent units of code that will replace lines start_line through end_line
    - Exact indentation matching the source
-   - Complete code that can directly replace the original
+   - All lines needed for the change, no eliding with comments
+   - Strip any line number prefixes from the output code
 
 5. When fixing code, check and address any diagnostics issues.
 
@@ -76,7 +88,7 @@ Your task is to modify the provided code according to the user's request. Follow
    - End with "**`[Response truncated] Please ask for the remaining changes.`**"
    - Next response should continue with the next code block
 
-Remember: Your response should ONLY contain file headers with line numbers and code blocks for direct replacement.
+Remember: Each block must represent an exact replacement of the specified line range.
 ]]
 
 ---@type table<string, CopilotChat.config.prompt>