Core: Categorize UniversalStore follower timeout error

code/core/src/manager-errors.ts

@@ -18,6 +18,7 @@ export enum Category {
   MANAGER_CORE_EVENTS = 'MANAGER_CORE-EVENTS',
   MANAGER_ROUTER = 'MANAGER_ROUTER',
   MANAGER_THEMING = 'MANAGER_THEMING',
+  MANAGER_UNIVERSAL_STORE = 'MANAGER_UNIVERSAL-STORE',
 }
 
 export class ProviderDoesNotExtendBaseProviderError extends StorybookError {
@@ -66,3 +67,14 @@ export class StatusTypeIdMismatchError extends StorybookError {
     });
   }
 }
+
+export class UniversalStoreFollowerTimeoutError extends StorybookError {
+  constructor(followerId: string) {
+    super({
+      name: 'UniversalStoreFollowerTimeoutError',
+      category: Category.MANAGER_UNIVERSAL_STORE,
+      code: 1,
+      message: `Timed out waiting for leader state for UniversalStore follower with id: '${followerId}'. Ensure a leader with the same id exists and is reachable before creating a follower.`,
+    });
+  }
+}

code/core/src/shared/universal-store/index.test.ts

@@ -6,6 +6,7 @@ import { UniversalStore } from './index.ts';
 import { instances as mockedInstances } from './__mocks__/instances.ts';
 import { MockUniversalStore } from './mock.ts';
 import type { ChannelEvent } from './types.ts';
+import { UniversalStoreFollowerTimeoutError } from '../../manager-errors.ts';
 
 vi.mock('./instances');
 
@@ -690,8 +691,8 @@ You should reuse the existing instance instead of trying to create a new one.`);
 
         // Assert - eventually the follower.untilReady() promise should throw an error when the timeout is reached
         vi.advanceTimersToNextTimer();
-        await expect(follower.untilReady()).rejects.toThrowErrorMatchingInlineSnapshot(
-          `[TypeError: No existing state found for follower with id: 'env1:test'. Make sure a leader with the same id exists before creating a follower.]`
+        await expect(follower.untilReady()).rejects.toBeInstanceOf(
+          UniversalStoreFollowerTimeoutError
         );
         expect(follower.status).toBe(UniversalStore.Status.ERROR);
       });

code/core/src/shared/universal-store/index.ts

@@ -16,6 +16,7 @@ import type {
   StatusType,
   StoreOptions,
 } from './types.ts';
+import { UniversalStoreFollowerTimeoutError } from '../../manager-errors.ts';
 
 const CHANNEL_EVENT_PREFIX = 'UNIVERSAL_STORE:' as const;
 
@@ -542,13 +543,7 @@ export class UniversalStore<
       );
       // 2. Wait 1 sec for a response, then reject the syncing promise if not already resolved
       setTimeout(() => {
-        // if the state is already resolved by a response before this timeout,
-        // rejecting it doesn't do anything, it will be ignored
-        this.syncing!.reject!(
-          new TypeError(
-            `No existing state found for follower with id: '${this.id}'. Make sure a leader with the same id exists before creating a follower.`
-          )
-        );
+        this.syncing!.reject!(new UniversalStoreFollowerTimeoutError(this.id));
       }, 1000);
     }
   }