Fix: Patch structuredClone to error on $state proxies

.changeset/weak-flowers-sit.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+patch structuredClone in dev to error on $state proxies

documentation/docs/98-reference/.generated/shared-errors.md

@@ -60,6 +60,12 @@ Certain lifecycle methods can only be used during component initialisation. To f
 `%name%` is not a store with a `subscribe` method
 ```
 
+### structured_clone_state_proxy
+
+```
+To correctly clone a `$state` proxy, use `$state.snapshot` instead of `structuredClone`
+```
+
 ### svelte_element_invalid_this_value
 
 ```

packages/svelte/messages/shared-errors/errors.md

@@ -52,6 +52,10 @@ Certain lifecycle methods can only be used during component initialisation. To f
 
 > `%name%` is not a store with a `subscribe` method
 
+## structured_clone_state_proxy
+
+> To correctly clone a `$state` proxy, use `$state.snapshot` instead of `structuredClone`
+
 ## svelte_element_invalid_this_value
 
 > The `this` prop on `<svelte:element>` must be a string, if defined