feat(core): decouple structured output from Groupped trait

Introduce `StructuralData` sealed trait and `pack_structural!` /
`group_structural!` / `derive(StructuralData)` macros to control
structured rendering separately from grouping. `Groupped` no longer
requires `Serialize`.

1 files changed, 15 insertions, 0 deletions

diff --git a/mingling_core/src/lib.rs b/mingling_core/src/lib.rs
index ddb5446..9d0ac2a 100644
--- a/mingling_core/src/lib.rs
+++ b/mingling_core/src/lib.rs
@@ -22,6 +22,9 @@ pub mod test {
 #[cfg(feature = "general_renderer")]
 pub use crate::renderer::general::GeneralRenderer;
 
+// NOT re-exported at top level: the `StructuralData` trait is sealed and only
+// accessible through the derive macro. Users who need the trait can access it
+// via `mingling::renderer::general::StructuralData` (through the inner alias).
 pub use crate::any::group::*;
 pub use crate::any::*;
 
@@ -72,6 +75,18 @@ pub mod setup {
     pub use crate::program::setup::ProgramSetup;
 }
 
+/// Private API — not intended for direct use.
+#[doc(hidden)]
+pub mod __private {
+    /// Sealed trait for `StructuralData` — only implementable via derive macro.
+    pub trait StructuralDataSealed {}
+
+    /// Re-export so the derive macro can reference the trait without
+    /// conflicting with the derive macro name at `::mingling::StructuralData`.
+    #[cfg(feature = "general_renderer")]
+    pub use crate::renderer::general::structural_data::StructuralData;
+}
+
 #[doc(hidden)]
 pub mod core_res {
     #[cfg(feature = "repl")]