Add message parsing system documentation

Add Overview.md documenting the core message parsing system architecture,
components, and usage patterns.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/core/message-parsing/Overview.md

@@ -0,0 +1,134 @@
+# Message Parsing System
+
+This directory contains the core message parsing system that processes AI assistant responses and converts them into structured directives that the extension can execute.
+
+## Overview
+
+The message parsing system is responsible for:
+
+- Parsing streaming AI responses containing XML-formatted directives
+- Handling mixed content (text + XML tools + code blocks)
+- Converting parsed content into actionable directives
+- Managing parsing state and error recovery
+
+## Core Components
+
+### Main Parser
+
+- **`DirectiveStreamingParser.ts`** - Primary streaming XML parser using SAX
+- **`ParseContext.ts`** - Parsing state management and context tracking
+- **`presentAssistantMessage.ts`** - Main entry point for processing assistant messages
+
+### Directive System
+
+- **`directives/`** - Defines the core directive types:
+    - `TextDirective` - Plain text content
+    - `ToolDirective` - Tool execution commands
+    - `LogDirective` - Logging and debugging output
+    - `Directive.ts` - Union type for all directive types
+
+### Tool Directives
+
+- **`directives/tool-directives/`** - Specific tool implementations:
+    - File operations: `ReadFileToolDirective`, `WriteToFileToolDirective`
+    - Code manipulation: `SearchAndReplaceToolDirective`, `InsertCodeBlockToolDirective`
+    - System interaction: `ExecuteCommandToolDirective`, `BrowserActionToolDirective`
+    - Navigation: `ListFilesToolDirective`, `SearchFilesToolDirective`
+    - MCP integration: `UseMcpToolToolDirective`, `AccessMcpResourceToolDirective`
+    - Task management: `NewTaskToolDirective`, `AttemptCompletionToolDirective`
+
+### Handler System
+
+- **`handlers/`** - Directive-specific parsing handlers:
+    - `BaseDirectiveHandler.ts` - Base class for all handlers
+    - `TextDirectiveHandler.ts` - Handles plain text content
+    - `ToolDirectiveHandler.ts` - Handles tool execution directives
+    - `LogDirectiveHandler.ts` - Handles logging directives
+
+### Registry & Factory
+
+- **`DirectiveHandlerRegistry.ts`** - Registry for mapping XML tags to handlers
+- **`DirectiveRegistryFactory.ts`** - Factory for creating handler registries
+- **`DirectiveHandler.ts`** - Base directive handler interface
+
+### Parsing Utilities
+
+- **`CodeBlockStateMachine.ts`** - State machine for handling code block parsing
+- **`FallbackParser.ts`** - Fallback parser for malformed XML
+- **`ParameterCodeBlockHandler.ts`** - Specialized handler for parameter code blocks
+- **`XmlUtils.ts`** - XML parsing utilities and helpers
+
+## Key Features
+
+### Streaming Parser
+
+The system uses a SAX-based streaming parser that can handle:
+
+- Incomplete XML messages (streaming in progress)
+- Mixed content (text, XML, and code blocks)
+- Malformed XML with graceful fallback
+- Code block detection and preservation
+
+### State Management
+
+The `ParseContext` tracks:
+
+- Current parsing state
+- Code block boundaries
+- XML tag completion status
+- Content accumulation
+
+### Error Recovery
+
+- Graceful handling of incomplete XML during streaming
+- Fallback parsing for malformed content
+- Preservation of partial tool directives
+
+### Tool Integration
+
+Each tool directive corresponds to a specific AI capability:
+
+- File system operations
+- Terminal command execution
+- Web browser automation
+- Code search and manipulation
+- MCP (Model Context Protocol) tool usage
+
+## Usage
+
+```typescript
+import { DirectiveStreamingParser } from "./DirectiveStreamingParser"
+
+// Parse assistant message into directives
+const directives = DirectiveStreamingParser.parse(assistantMessage)
+
+// Process each directive
+for (const directive of directives) {
+	switch (directive.type) {
+		case "text":
+			// Handle text content
+			break
+		case "tool_use":
+			// Execute tool with directive.name and directive.params
+			break
+		case "log":
+			// Handle logging directive
+			break
+	}
+}
+```
+
+## Testing
+
+The `__tests__/` directory contains comprehensive tests for:
+
+- Core parser functionality
+- State machine behavior
+- Fallback parsing scenarios
+- Individual directive parsing
+
+Run tests with:
+
+```bash
+pnpm test
+```