2 files changed, 83 insertions, 0 deletions
diff --git a/mingling_core/src/renderer/structural/error.rs b/mingling_core/src/renderer/structural/error.rs
new file mode 100644
index 0000000..a7fbc75
--- /dev/null
+++ b/mingling_core/src/renderer/structural/error.rs
@@ -0,0 +1,68 @@
+/// Represents an error that occurs during serialization of a structural renderer.
+///
+/// This error stores a human-readable message describing what went wrong
+/// during the serialization process.
+#[derive(Debug)]
+pub struct StructuralRendererSerializeError {
+    /// The underlying error message.
+    error: String,
+}
+
+impl StructuralRendererSerializeError {
+    #[must_use]
+    pub fn new(error: String) -> Self {
+        Self { error }
+    }
+}
+
+impl From<&str> for StructuralRendererSerializeError {
+    fn from(s: &str) -> Self {
+        Self::new(s.to_string())
+    }
+}
+
+impl std::ops::Deref for StructuralRendererSerializeError {
+    type Target = String;
+
+    fn deref(&self) -> &Self::Target {
+        &self.error
+    }
+}
+
+impl From<StructuralRendererSerializeError> for String {
+    fn from(val: StructuralRendererSerializeError) -> Self {
+        val.error
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn new_creates_error_with_message() {
+        let msg = "serialization failed".to_string();
+        let err = StructuralRendererSerializeError::new(msg.clone());
+        assert_eq!(err.error, msg);
+    }
+
+    #[test]
+    fn from_str_creates_error_from_string_slice() {
+        let err: StructuralRendererSerializeError = "oops".into();
+        assert_eq!(err.error, "oops");
+    }
+
+    #[test]
+    fn deref_accesses_inner_error_string() {
+        let err = StructuralRendererSerializeError::new("inner message".to_string());
+        let derefed: &String = &err;
+        assert_eq!(derefed, "inner message");
+    }
+
+    #[test]
+    fn into_string_extracts_message() {
+        let err = StructuralRendererSerializeError::new("extract me".to_string());
+        let s: String = err.into();
+        assert_eq!(s, "extract me");
+    }
+}
diff --git a/mingling_core/src/renderer/structural/structural_data.rs b/mingling_core/src/renderer/structural/structural_data.rs
new file mode 100644
index 0000000..1cafac3
--- /dev/null
+++ b/mingling_core/src/renderer/structural/structural_data.rs
@@ -0,0 +1,15 @@
+use serde::Serialize;
+
+/// Marker trait for types that support structured output (JSON / YAML / TOML / RON).
+///
+/// This trait is a **supertrait** of `serde::Serialize` and is sealed via
+/// `__private::StructuralDataSealed`. It can only be implemented through:
+///
+/// - `#[derive(StructuralData)]`
+/// - `pack_structural!`
+/// - `group_structural!`
+///
+/// These entry points also register the type in the global `STRUCTURED_TYPES`
+/// registry, which is required for the `structural_render` match arm to be generated.
+#[doc(hidden)]
+pub trait StructuralData: Serialize + crate::__private::StructuralDataSealed {}