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+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+**dosage** is a DOS-style command shell implementation written in Rust. The project aims to recreate classic DOS commands and shell functionality in a modern Rust environment, providing a nostalgic DOS computing experience.
+
+## Development Commands
+
+```bash
+# Development
+cargo run                 # Run in debug mode with REPL shell
+cargo build              # Build debug version  
+cargo check              # Fast syntax/type checking
+cargo clean              # Clean build artifacts
+
+# Release builds (heavily optimized for size)
+cargo build --release    # Optimized build with LTO and size optimization
+cargo run --release      # Run optimized version
+```
+
+## Architecture
+
+### Command System Design
+The application uses a type-safe command architecture with Rust enums:
+
+- **`Command`**: Top-level enum supporting pipes, redirections, external programs, and builtins
+- **`BuiltinCommand`**: Comprehensive DOS command set covering file operations, shell control, scripting, and utilities
+- **`FileSpec`**: Handles console (`Con`) vs file path targets for I/O redirection
+
+### Current Implementation Status
+- **Implemented**: Basic REPL shell with `rustyline` for interactive input
+- **Stubbed**: Command parsing (`parse` method returns "Not implemented")  
+- **Planned**: Full DOS command execution based on the `BuiltinCommand` enum
+
+### Key DOS Commands Planned
+File operations (`type`, `copy`, `xcopy`, `dir`, `tree`), shell control (`prompt`, `echo`, `set`, `chdir`), and classic utilities (`date`, `time`, `cls`, `mem`).
+
+### Error Handling
+Uses modern Rust error handling with `eyre::Result` and `color-eyre` for enhanced error reporting with colored output.
+
+### Dependencies
+- **`rustyline`**: Interactive command-line editing and history
+- **`crossterm`**: Cross-platform terminal manipulation
+- **`prettytable-rs`**: Table formatting for command output
+- **`eyre`/`color-eyre`**: Enhanced error handling and reporting
+- **`thiserror`**: Error type derivation macros
+
+## Release Optimization
+The release profile is configured for maximum size optimization with LTO, `opt-level = "z"`, symbol stripping, and single codegen unit compilation.
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