fix, only warn in dev

packages/svelte/src/internal/client/proxy.js

@@ -298,14 +298,13 @@ export function proxy(value) {
  * @returns {T | void}
  */
 export function return_proxy(value) {
-	if (
+	if (should_proxy(value)) {
-		!should_proxy(value) &&
-		!(typeof value === 'object' && value !== null && STATE_SYMBOL in value)
-	) {
-		// if the argument passed was already a proxy, we don't warn
 		return proxy(value);
-	}
+	} else if (DEV && !(typeof value === 'object' && value !== null && STATE_SYMBOL in value)) {
+		// if the argument passed was already a proxy, we don't warn
 		w.state_return_not_proxyable();
+	}
+	return value;
 }
 
 /**