feat(core): rename `builds` feature to `build`

Replace the `builds` feature with `build` across the crate, keeping
a backward-compatible alias for the old name.  Update all internal
visibility from `#[doc(hidden)] pub mod` to `pub(crate) mod` and
reorganize the `__private` module into a dedicated `private.rs`.

1 files changed, 12 insertions, 0 deletions

diff --git a/mingling_core/src/private.rs b/mingling_core/src/private.rs
new file mode 100644
index 0000000..371ada2
--- /dev/null
+++ b/mingling_core/src/private.rs
@@ -0,0 +1,12 @@
+/// Sealed trait for `StructuralData` — only implementable via derive macro.
+#[cfg(feature = "structural_renderer")]
+pub trait StructuralDataSealed<C>
+where
+    C: crate::ProgramCollect<Enum = C>,
+{
+}
+
+/// Re-export so the derive macro can reference the trait without
+/// conflicting with the derive macro name at `::mingling::StructuralData`.
+#[cfg(feature = "structural_renderer")]
+pub use crate::renderer::structural::structural_data::StructuralData;