chore: checkpoint before Python removal

vendor/clap/examples/derive_ref/augment_subcommands.rs

@@ -0,0 +1,21 @@
+use clap::{Command, FromArgMatches as _, Parser, Subcommand as _};
+
+#[derive(Parser, Debug)]
+enum Subcommands {
+    Derived {
+        #[arg(short, long)]
+        derived_flag: bool,
+    },
+}
+
+fn main() {
+    let cli = Command::new("Built CLI");
+    // Augment with derived subcommands
+    let cli = Subcommands::augment_subcommands(cli);
+
+    let matches = cli.get_matches();
+    let derived_subcommands = Subcommands::from_arg_matches(&matches)
+        .map_err(|err| err.exit())
+        .unwrap();
+    println!("Derived subcommands: {derived_subcommands:#?}");
+}