feat: lookup at downgrade time

works, but leaks memory

src/ty/internal/primop.rs

@@ -73,13 +73,17 @@ impl<'gc> PartialPrimOp<'gc> {
         mc: &Mutation<'gc>,
     ) -> Result<Value<'gc>> {
         let func = self.func;
-        let self_mut = self.make_mut(mc);
-        self_mut.args.push(arg);
-        self_mut.arity -= 1;
-        if self_mut.arity > 0 {
-            Value::PartialPrimOp(self.clone()).ok()
-        } else {
-            func(std::mem::take(&mut self_mut.args), vm, mc)
-        }
+        let Some(ret) = self.make_mut(|self_mut| {
+            self_mut.args.push(arg);
+            self_mut.arity -= 1;
+            if self_mut.arity == 0 {
+                Some(func(std::mem::take(&mut self_mut.args), vm, mc))
+            } else {
+                None
+            }
+        }, mc) else {
+            return Value::PartialPrimOp(self.clone()).ok();
+        };
+        ret
     }
 }