Validate unified source and native positional call contracts

crates/objects/src/object.rs

@@ -117,6 +117,11 @@ pub trait ObjectPayload: Any + fmt::Debug + Send + Sync {
     /// Host-call entry: arguments and raw results are borrowed handles. The VM
     /// validates/retains the result before exposing it as an owned call result.
     /// Language functions are dispatched by Vm's frame evaluator instead.
+    /// Positional metadata for native call protocols; source code is queried by the store.
+    fn call_arity(&self) -> Option<crate::CallArity> {
+        self.native_callable().and_then(|callable| callable.arity())
+    }
+
     fn call(&self, _arguments: &[Value]) -> Result<Value, VmError> {
         Err(VmError::UnsupportedOperation("call"))
     }
@@ -176,6 +181,7 @@ pub type NativeCall = EndorNativeCall;
 pub struct EndorNativeFunctionObject {
     name: String,
     function: NativeCall,
+    arity: Option<crate::CallArity>,
 }
 
 impl EndorNativeFunctionObject {
@@ -183,12 +189,17 @@ impl EndorNativeFunctionObject {
         Self {
             name: name.into(),
             function,
+            arity: None,
         }
     }
 
     pub fn name(&self) -> &str {
         &self.name
     }
+    pub fn with_arity(mut self, arity: crate::CallArity) -> Self {
+        self.arity = Some(arity);
+        self
+    }
 }
 
 /// Compatibility name for existing embedders.
@@ -213,7 +224,13 @@ impl ObjectPayload for EndorNativeFunctionObject {
         Ok(format!("<native-function {}>", self.name))
     }
 
+    fn call_arity(&self) -> Option<crate::CallArity> {
+        self.arity
+    }
     fn call(&self, arguments: &[Value]) -> Result<Value, VmError> {
+        if let Some(arity) = self.arity {
+            arity.check(self.name.clone(), arguments.len())?;
+        }
         (self.function)(arguments)
     }
 }