feat: add AES-128-CBC decryption and clap CLI (M4)

Add session key derivation and payload decryption using AES-128-CBC
with well-known XEX2 master keys. Refactor CLI to use clap with
inspect/extract subcommands. Extend FileFormatInfo to parse
compression metadata (basic blocks, LZX window size/block chain).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/main.rs

@@ -1,31 +1,77 @@
+use clap::{Parser, Subcommand};
+use std::path::PathBuf;
 use std::process;
 
+/// A tool for extracting and inspecting Xbox 360 XEX2 executable files.
+#[derive(Parser)]
+#[command(name = "xex2tractor", version, about)]
+struct Cli {
+    #[command(subcommand)]
+    command: Command,
+}
+
+#[derive(Subcommand)]
+enum Command {
+    /// Display XEX2 file information (headers, security info, etc.)
+    Inspect {
+        /// Path to the XEX2 file
+        file: PathBuf,
+    },
+    /// Extract the PE image from a XEX2 file
+    Extract {
+        /// Path to the XEX2 file
+        file: PathBuf,
+        /// Output path for the extracted PE file (default: same name with .exe extension)
+        output: Option<PathBuf>,
+    },
+}
+
 fn main() {
-    let path = match std::env::args().nth(1) {
-        Some(p) => p,
-        None => {
-            eprintln!("Usage: xex2tractor <file.xex>");
-            process::exit(1);
-        }
-    };
+    let cli = Cli::parse();
 
-    let data = match std::fs::read(&path) {
-        Ok(d) => d,
-        Err(e) => {
-            eprintln!("Error reading {path}: {e}");
-            process::exit(1);
-        }
-    };
+    match cli.command {
+        Command::Inspect { file } => cmd_inspect(&file),
+        Command::Extract { file, output } => cmd_extract(&file, output),
+    }
+}
 
-    let xex = match xex2tractor::parse(&data) {
-        Ok(x) => x,
-        Err(e) => {
-            eprintln!("Error parsing XEX2: {e}");
-            process::exit(1);
-        }
-    };
+fn cmd_inspect(path: &PathBuf) {
+    let data = read_file(path);
+    let xex = parse_xex(&data);
 
     xex2tractor::display::display_header(&xex.header);
     xex2tractor::display::display_optional_headers(&xex.optional_headers);
     xex2tractor::display::display_security_info(&xex.security_info);
 }
+
+fn cmd_extract(path: &PathBuf, output: Option<PathBuf>) {
+    let _output_path = output.unwrap_or_else(|| path.with_extension("exe"));
+
+    let data = read_file(path);
+    let _xex = parse_xex(&data);
+
+    // TODO(M5): decrypt + decompress pipeline
+    // TODO(M6): verify PE and write to output_path
+    eprintln!("Error: extraction not yet implemented (coming in M5/M6)");
+    process::exit(1);
+}
+
+fn read_file(path: &PathBuf) -> Vec<u8> {
+    match std::fs::read(path) {
+        Ok(d) => d,
+        Err(e) => {
+            eprintln!("Error reading {}: {e}", path.display());
+            process::exit(1);
+        }
+    }
+}
+
+fn parse_xex(data: &[u8]) -> xex2tractor::Xex2File {
+    match xex2tractor::parse(data) {
+        Ok(x) => x,
+        Err(e) => {
+            eprintln!("Error parsing XEX2: {e}");
+            process::exit(1);
+        }
+    }
+}