fix(oauth): follower last-chance read after poll deadline (#4718)

* fix(oauth): follower last-chance read after poll deadline

* test(oauth): exercise last-chance read in follower timeout test

apps/sim/lib/concurrency/__tests__/leader-lock.test.ts

@@ -117,6 +117,30 @@ describe('withLeaderLock', () => {
     expect(onFollower.mock.calls.length).toBeGreaterThanOrEqual(2)
   })
 
+  it('follower does a final read after timeout to catch a just-finished leader', async () => {
+    redisConfigMockFns.mockAcquireLock.mockResolvedValueOnce(false)
+
+    // pollInterval=5, maxWait=9 → loop exits after 2 in-loop polls (T+5, T+10);
+    // the third call (polls=3) is the post-deadline last-chance read.
+    let polls = 0
+    const onFollower = vi.fn(async () => {
+      polls += 1
+      if (polls <= 2) return null
+      return 'late-leader'
+    })
+
+    const result = await withLeaderLock<string>({
+      key: 'k',
+      pollIntervalMs: 5,
+      maxWaitMs: 9,
+      onLeader: async () => 'should-not-run',
+      onFollower,
+    })
+
+    expect(result).toBe('late-leader')
+    expect(onFollower).toHaveBeenCalledTimes(3)
+  })
+
   it('follower returns null after timeout', async () => {
     redisConfigMockFns.mockAcquireLock.mockResolvedValueOnce(false)
 

apps/sim/lib/concurrency/leader-lock.ts

@@ -64,6 +64,10 @@ export async function withLeaderLock<T>(opts: LeaderLockOptions<T>): Promise<T |
     if (value !== null) return value
   }
 
+  // The leader may have persisted between our final poll and now; one last check.
+  const lastChance = await onFollower()
+  if (lastChance !== null) return lastChance
+
   logger.warn('Follower timed out waiting for leader', { key, maxWaitMs })
   return null
 }