fix(web/default): guard playground messages against legacy classic shape (#4650)

fix(playground): handle legacy localStorage message shape

Sanitizes old-format saved messages to prevent 500 on playground load.

web/default/src/features/playground/lib/storage.ts

@@ -88,8 +88,12 @@ export function loadMessages(): Message[] | null {
   try {
   try {
     const saved = localStorage.getItem(STORAGE_KEYS.MESSAGES)
     const saved = localStorage.getItem(STORAGE_KEYS.MESSAGES)
     if (saved) {
     if (saved) {
-      const parsed: Message[] = JSON.parse(saved)
-      const sanitized = sanitizeMessagesOnLoad(parsed)
+      const parsed: unknown = JSON.parse(saved)
+      if (!Array.isArray(parsed)) {
+        localStorage.removeItem(STORAGE_KEYS.MESSAGES)
+        return null
+      }
+      const sanitized = sanitizeMessagesOnLoad(parsed as Message[])
       // Persist sanitized result to avoid re-sanitizing on subsequent loads
       // Persist sanitized result to avoid re-sanitizing on subsequent loads
       if (sanitized !== parsed) {
       if (sanitized !== parsed) {
         saveMessages(sanitized)
         saveMessages(sanitized)