Add compile-time leaf declarations

Introduce a function-like leaf declaration macro, bind endpoint and TUI hosts to shared generated metadata, and move remote shell endpoint construction out of the leaf module into the examples and runtime assembly code.

unshell-macros/src/lib.rs

@@ -1,6 +1,7 @@
 //! Proc macros for `unshell` application-layer leaf declarations.
 
 mod leaf;
+mod leaf_decl;
 mod procedure;
 mod procedures;
 mod utils;
@@ -8,6 +9,35 @@ mod utils;
 use proc_macro::TokenStream;
 use syn::{DeriveInput, ItemImpl, parse_macro_input};
 
+/// Declares one compile-time leaf surface and binds it to endpoint and/or TUI
+/// host structs.
+///
+/// What it is: a function-like macro that generates the shared protocol-visible
+/// metadata for one leaf and applies that metadata to the listed host structs.
+///
+/// Why it exists: endpoint and TUI hosts should not each have to repeat the leaf
+/// name and procedure inventory, and endpoint construction should not need a
+/// handwritten list of procedure ids.
+///
+/// # Example
+/// ```ignore
+/// unshell::leaf! {
+///     name = "remote_shell",
+///     procedures = [Open, Reset, whoami],
+///     endpoint_struct = RemoteShellEndpoint,
+///     tui_struct = RemoteShellTui,
+/// }
+/// ```
+#[proc_macro]
+pub fn leaf(input: TokenStream) -> TokenStream {
+    match leaf_decl::expand_leaf_declaration(parse_macro_input!(
+        input as leaf_decl::LeafDeclarationInput
+    )) {
+        Ok(tokens) => tokens.into(),
+        Err(error) => error.to_compile_error().into(),
+    }
+}
+
 /// Derives canonical protocol-leaf identity helpers for one host type.
 ///
 /// What it is: a derive macro that implements `ProtocolLeaf` and generates the