feat: add entry metadata system with compile-time typed values

Add `Metadata<B>` trait and `#[metadata(Entry)]` attribute macro
to attach arbitrary, compile-time-typed metadata to entries.
Implement `ProgramCollect::get_metadata<T>()` for runtime retrieval,
backed by a global registry populated by `register_metadata!`.

Extend `pathf` with `MetadataPattern` to resolve metadata types
across modules at build time. Add two examples demonstrating
metadata usage with and without pathf integration.

1 files changed, 12 insertions, 0 deletions

diff --git a/mingling_core/src/program/collection.rs b/mingling_core/src/program/collection.rs
index 1b4d7dd..5b1152a 100644
--- a/mingling_core/src/program/collection.rs
+++ b/mingling_core/src/program/collection.rs
@@ -66,6 +66,18 @@ pub trait ProgramCollect {
     /// Render help for Entry
     fn render_help(any: AnyOutput<Self::Enum>) -> RenderResult;
 
+    /// Retrieves compile-time registered metadata of type `T` for the given
+    /// enum member, if any was registered via `#[metadata(Entry)]`.
+    ///
+    /// Returns `None` when no metadata of type `T` has been registered for the
+    /// provided member, or when the requested `T` does not match the registered
+    /// metadata type. The concrete implementation of this method is generated
+    /// by the `gen_program!` macro.
+    fn get_metadata<T: 'static>(member_id: Self::Enum) -> Option<T> {
+        let _ = member_id;
+        None
+    }
+
     /// Find a matching chain to continue execution based on the input [AnyOutput](./struct.AnyOutput.html), returning a new [AnyOutput](./struct.AnyOutput.html)
     #[cfg(feature = "async")]
     fn do_chain(