fix: validate usePluginData return type against default value

packages/omniviewdev-runtime/src/hooks/data/usePluginData.ts

@@ -8,6 +8,21 @@ type UsePluginDataResult<T> = {
   isLoading: boolean;
 };
 
+/**
+ * Check whether a value from the data store structurally matches the expected
+ * type indicated by the default value. This catches cases where the Go backend
+ * returns a JSON type that doesn't match the TypeScript generic (e.g. an object
+ * was stored but the caller expects an array).
+ */
+function matchesShape<T>(value: unknown, defaultValue: T): value is T {
+  if (defaultValue === null) return value === null;
+  if (Array.isArray(defaultValue)) return Array.isArray(value);
+  if (typeof defaultValue === 'object') {
+    return typeof value === 'object' && value !== null && !Array.isArray(value);
+  }
+  return typeof value === typeof defaultValue;
+}
+
 /**
  * Generic hook for reading/writing plugin data from the Plugin Data Store.
  * Uses React Query for caching and optimistic updates.
@@ -28,6 +43,14 @@ export function usePluginData<T>(
       if (result === null || result === undefined) {
         return defaultValue;
       }
+      if (!matchesShape(result, defaultValue)) {
+        console.warn(
+          `[usePluginData] stored value for "${key}" has unexpected type ` +
+          `(expected ${Array.isArray(defaultValue) ? 'array' : typeof defaultValue}, ` +
+          `got ${Array.isArray(result) ? 'array' : typeof result}). Using default.`,
+        );
+        return defaultValue;
+      }
       return result as T;
     },
   });