Guard cache eviction on identity and use createDeferred in test

Only delete the cache entry on error if the map still holds the same
promise, preventing a stale rejection from evicting a newer entry.
Also switch the test to createDeferred for readability.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Fredrik Adelöw <freben@gmail.com>

packages/backend-defaults/src/entrypoints/userInfo/CachedUserInfoService.test.ts

@@ -19,6 +19,7 @@ import {
   UserInfoService,
 } from '@backstage/backend-plugin-api';
 import { mockCredentials } from '@backstage/backend-test-utils';
+import { createDeferred } from '@backstage/types';
 import {
   CachedUserInfoService,
   UserInfoCacheEntry,
@@ -129,10 +130,8 @@ describe('CachedUserInfoService', () => {
   });
 
   it('evicts eagerly so concurrent waiters see the rejection and the next call retries', async () => {
-    let rejectFirst: (error: Error) => void;
-    const firstCall = new Promise<BackstageUserInfo>((_resolve, reject) => {
-      rejectFirst = reject;
-    });
+    const firstCall = createDeferred<BackstageUserInfo>();
+    firstCall.catch(() => {});
 
     const delegate: UserInfoService = {
       getUserInfo: jest
@@ -146,7 +145,7 @@ describe('CachedUserInfoService', () => {
     const p1 = service.getUserInfo(creds);
     const p2 = service.getUserInfo(creds);
 
-    rejectFirst!(new Error('boom'));
+    firstCall.reject(new Error('boom'));
 
     await expect(p1).rejects.toThrow('boom');
     await expect(p2).rejects.toThrow('boom');

packages/backend-defaults/src/entrypoints/userInfo/CachedUserInfoService.ts

@@ -73,7 +73,9 @@ export class CachedUserInfoService implements UserInfoService {
     }
 
     const promise = this.#delegate.getUserInfo(credentials).catch(error => {
-      this.#entries.delete(token);
+      if (this.#entries.get(token)?.promise === promise) {
+        this.#entries.delete(token);
+      }
       throw error;
     });