feat: implement schema validation and sample normalization

crates/mcpaas-schema/src/error.rs

@@ -0,0 +1,55 @@
+use thiserror::Error;
+
+#[derive(Clone, Debug, PartialEq, Eq, Error)]
+pub enum SchemaError {
+    #[error("missing required field at {path}")]
+    MissingField { path: String },
+    #[error("invalid value at {path}: expected {expected}, got {actual}")]
+    InvalidType {
+        path: String,
+        expected: &'static str,
+        actual: &'static str,
+    },
+    #[error("invalid enum value at {path}: expected one of {expected:?}, got {actual}")]
+    InvalidEnumValue {
+        path: String,
+        expected: Vec<String>,
+        actual: String,
+    },
+    #[error("no matching oneof variant at {path}")]
+    OneofMismatch { path: String },
+}
+
+impl SchemaError {
+    pub fn missing_field(path: impl Into<String>) -> Self {
+        Self::MissingField { path: path.into() }
+    }
+
+    pub fn invalid_type(
+        path: impl Into<String>,
+        expected: &'static str,
+        actual: &'static str,
+    ) -> Self {
+        Self::InvalidType {
+            path: path.into(),
+            expected,
+            actual,
+        }
+    }
+
+    pub fn invalid_enum_value(
+        path: impl Into<String>,
+        expected: Vec<String>,
+        actual: impl Into<String>,
+    ) -> Self {
+        Self::InvalidEnumValue {
+            path: path.into(),
+            expected,
+            actual: actual.into(),
+        }
+    }
+
+    pub fn oneof_mismatch(path: impl Into<String>) -> Self {
+        Self::OneofMismatch { path: path.into() }
+    }
+}