Refactor VTAgent to remove multi-agent support and enhance single-agent functionality

- Updated ContextCompressor to preserve decision ledger summaries.
- Added methods in DecisionTracker for recording user goals and rendering decision ledgers.
- Removed unused imports and multi-agent related code from various modules.
- Simplified Router logic by eliminating multi-agent decision-making.
- Enhanced TrajectoryLogger to log routing decisions and actions.
- Updated user confirmation prompts to reflect single-agent mode.
- Adjusted SafetyValidator to validate agent mode for single-agent usage.
- Removed multi-agent configuration from TOML files and tests.
- Added new tests for file writing and editing functionalities.

Author: vinhnx

.ruler/AGENTS.md

@@ -2,54 +2,53 @@
 
 ## Overview
 
-This document summarizes the implementation of advanced features in VTAgent, including debug mode for multi-agent systems, safety controls, and error recovery mechanisms.
+This document summarizes the implementation of advanced features in VTAgent, safety controls, and error recovery mechanisms.
 
 ## Debug Mode Implementation
 
-### Overview
-Debug mode provides comprehensive logging and error recovery for the multi-agent system in VTAgent, along with fixes for malformed function call errors.
-
 ### Changes Made
 
 #### 1. Debug Mode Configuration
-- Added `debug_mode: bool` field to `MultiAgentConfig` struct
-- Added `DEBUG_MODE` constant to `MultiAgentDefaults` (default: false)
-- Updated `MultiAgentSystemConfig` to include `debug_mode` field
-- Added debug mode configuration to `vtagent.toml.example`
 
-#### 2. Multi-Agent Loop Improvements
-- **Malformed Function Call Handling**: Added proper error detection and recovery for `MALFORMED_FUNCTION_CALL` errors
-- **Debug Logging**: Comprehensive debug output when debug mode is enabled
-- **Error Recovery**: Automatic retry with simplified approach when function calls are malformed
+-   Added `debug_mode: bool` field to `MultiAgentConfig` struct
+-   Added `DEBUG_MODE` constant to `MultiAgentDefaults` (default: false)
+-   Updated `MultiAgentSystemConfig` to include `debug_mode` field
+-   Added debug mode configuration to `vtagent.toml.example`
 
 #### 3. Debug Features Added
 
 ##### Configuration Debug Info
+
 When debug mode is enabled, the system displays:
-- Session ID
-- Orchestrator model
-- Subagent model
-- Max concurrent subagents
+
+-   Session ID
+-   Orchestrator model
+-   Subagent model
+-   Max concurrent subagents
 
 ##### Conversation Debug Info
-- User input logging
-- Conversation length tracking
-- Response analysis (number of candidates, finish reasons)
+
+-   User input logging
+-   Conversation length tracking
+-   Response analysis (number of candidates, finish reasons)
 
 ##### Tool Execution Debug Info
-- Tool name and arguments before execution
-- Tool execution results (formatted JSON)
-- Error details when tool execution fails
+
+-   Tool name and arguments before execution
+-   Tool execution results (formatted JSON)
+-   Error details when tool execution fails
 
 ##### Loop Control Debug Info
-- Tool call detection status
-- Text response detection status
-- Loop continuation/termination reasons
-- No content/no candidates error tracking
+
+-   Tool call detection status
+-   Text response detection status
+-   Loop continuation/termination reasons
+-   No content/no candidates error tracking
 
 #### 4. Error Handling Improvements
 
 ##### Malformed Function Call Recovery
+
 ```rust
 if finish_reason == "MALFORMED_FUNCTION_CALL" {
     println!("(malformed function call in orchestrator - retrying with simpler approach)");
@@ -60,6 +59,7 @@ if finish_reason == "MALFORMED_FUNCTION_CALL" {
 ## Safety Implementation
 
 ### Overview
+
 Safety implementation adds critical safety and efficiency controls to VTAgent, ensuring user explicit confirmation for expensive operations and defaulting to single-agent mode for optimal resource usage.
 
 ### Key Safety Features Implemented
@@ -69,96 +69,98 @@ Safety implementation adds critical safety and efficiency controls to VTAgent, e
 **Critical Safety Requirement**: Before attempting to switch to the most capable model ("gemini-2.5-pro"), always ask for explicit user confirmation.
 
 **Implementation**:
-- Added `SafetyValidator::validate_model_usage()` function
-- Automatically detects when Gemini 2.5 Pro is requested
-- Shows clear warning about cost and performance implications:
-  ```
-   Model Upgrade Required
-  Current model: gemini-2.5-flash-lite
-  Requested model: gemini-2.5-pro
-
-  The Gemini 2.5 Pro model is the most capable but also:
-  • More expensive per token
-  • Slower response times
-  • Higher resource usage
-
-  Do you want to proceed with the more capable (and expensive) Gemini 2.5 Pro model?
-  ```
-- Falls back to default model if user declines
+
+-   Added `SafetyValidator::validate_model_usage()` function
+-   Automatically detects when Gemini 2.5 Pro is requested
+-   Shows clear warning about cost and performance implications:
+
+    ```
+     Model Upgrade Required
+    Current model: gemini-2.5-flash-lite
+    Requested model: gemini-2.5-pro
+
+    The Gemini 2.5 Pro model is the most capable but also:
+    • More expensive per token
+    • Slower response times
+    • Higher resource usage
+
+    Do you want to proceed with the more capable (and expensive) Gemini 2.5 Pro model?
+    ```
+
+-   Falls back to default model if user declines
 
 #### 2. Agent Mode Safety
 
-**Critical Efficiency Requirement**: The orchestrator must default to using one single simple coder agent for all tasks. Switch to a multi-agent setup only for complex tasks, and always ask for explicit user confirmation.
+**Critical Efficiency Requirement**: The orchestrator must default to using one single simple coder agent for all tasks.
 
 **Implementation**:
-- **Changed default**: `ENABLE_MULTI_AGENT` now defaults to `false` (single-agent mode)
-- Added `SafetyValidator::validate_agent_mode()` function
-- Automatic task complexity assessment:
-  ```
-  📊 Task Complexity Assessment
-  Task: [user's task description]
-
-  How would you classify this task's complexity?
-  > Simple (single file edit, basic question, straightforward task)
-    Moderate (multiple files, refactoring, testing)
-    Complex (architecture changes, cross-cutting concerns, large refactoring)
-  ```
-- Smart recommendations based on complexity:
-  - **Simple/Moderate**: Recommends single coder agent
-  - **Complex**: Recommends multi-agent with confirmation
+
+-   Added `SafetyValidator::validate_agent_mode()` function
+-   Automatic task complexity assessment:
+
+    ```
+    📊 Task Complexity Assessment
+    Task: [user's task description]
+
+    How would you classify this task's complexity?
+    > Simple (single file edit, basic question, straightforward task)
+      Moderate (multiple files, refactoring, testing)
+      Complex (architecture changes, cross-cutting concerns, large refactoring)
+    ```
+
+-   Smart recommendations based on complexity:
+    -   **Simple/Moderate**: Recommends single coder agent
 
 #### 3. Command Execution Safety
 
 **Security Controls**: Enhanced command execution with pattern-based validation and user confirmation for dangerous operations.
 
 **Implementation**:
-- Pattern-based command classification
-- Dangerous command detection (rm, dd, format, etc.)
-- User confirmation prompts for risky operations
-- Command allow/deny lists
-- Enhanced error handling for command execution
+
+-   Pattern-based command classification
+-   Dangerous command detection (rm, dd, format, etc.)
+-   User confirmation prompts for risky operations
+-   Command allow/deny lists
+-   Enhanced error handling for command execution
 
 #### 4. File Operation Safety
 
 **File System Protection**: Comprehensive file operation validation and safety checks.
 
 **Implementation**:
-- Path validation and normalization
-- Permission checking before file operations
-- .vtagentgitignore integration for file exclusions
-- Safe file writing with backup mechanisms
-- Directory traversal protection
+
+-   Path validation and normalization
+-   Permission checking before file operations
+-   .vtagentgitignore integration for file exclusions
+-   Safe file writing with backup mechanisms
+-   Directory traversal protection
 
 ## Integration and Testing
 
 ### Debug Mode Testing
-- Comprehensive test coverage for debug logging
-- Error recovery mechanism validation
-- Multi-agent loop stability testing
-- Performance impact assessment
+
+-   Comprehensive test coverage for debug logging
+-   Error recovery mechanism validation
+-   Performance impact assessment
 
 ### Safety Feature Testing
-- Model usage confirmation flow testing
-- Agent mode selection validation
-- Command execution safety verification
-- File operation security testing
+
+-   Model usage confirmation flow testing
+-   Agent mode selection validation
+-   Command execution safety verification
+-   File operation security testing
 
 ### Cross-Feature Integration
-- Debug mode and safety feature compatibility
-- Error handling integration testing
-- Performance monitoring and optimization
-- User experience validation
 
-## Configuration
+-   Debug mode and safety feature compatibility
+-   Error handling integration testing
+-   Performance monitoring and optimization
+-   User experience validation
 
-### Debug Mode Configuration
-```toml
-[multi_agent]
-enabled = true
-debug_mode = true  # Enable debug logging
-```
+## Configuration
 
 ### Safety Configuration
+
 ```toml
 [agent]
 # Safety settings
@@ -174,32 +176,36 @@ dangerous_commands_require_confirmation = true
 ## Performance Considerations
 
 ### Debug Mode Performance
-- Debug logging has minimal performance impact when disabled
-- Memory-efficient logging mechanisms
-- Configurable debug levels for different verbosity needs
-- Background logging to avoid blocking operations
+
+-   Debug logging has minimal performance impact when disabled
+-   Memory-efficient logging mechanisms
+-   Configurable debug levels for different verbosity needs
+-   Background logging to avoid blocking operations
 
 ### Safety Feature Performance
-- Lightweight validation checks
-- Efficient pattern matching for command classification
-- Cached file system permission checks
-- Minimal overhead for safety validations
+
+-   Lightweight validation checks
+-   Efficient pattern matching for command classification
+-   Cached file system permission checks
+-   Minimal overhead for safety validations
 
 ## Future Enhancements
 
 ### Planned Debug Features
-- Advanced debugging dashboard
-- Real-time performance monitoring
-- Enhanced error reporting and analytics
-- Debug data export capabilities
+
+-   Advanced debugging dashboard
+-   Real-time performance monitoring
+-   Enhanced error reporting and analytics
+-   Debug data export capabilities
 
 ### Planned Safety Features
-- Advanced threat detection
-- Machine learning-based anomaly detection
-- Enhanced audit logging
-- Automated security policy recommendations
+
+-   Advanced threat detection
+-   Machine learning-based anomaly detection
+-   Enhanced audit logging
+-   Automated security policy recommendations
 
 ---
 
-*This document covers the implementation of debug mode and safety features in VTAgent. For user-facing documentation, see the respective guide documents.*</content>
+_This document covers the implementation of debug mode and safety features in VTAgent. For user-facing documentation, see the respective guide documents._</content>
 <parameter name="filePath">/Users/vinh.nguyenxuan/Developer/learn-by-doing/vtagent/docs/ADVANCED_FEATURES_IMPLEMENTATION.md