test(autoassignment): stabilize concurrency diagnostics (#75)

Co-authored-by: Rogee <rogee@ipao.vip>

backend/internal/autoassignment/coverage9_test.go

@@ -227,9 +227,16 @@ func TestAssignmentServiceOnlyOneConcurrentWorkerWins(t *testing.T) {
 
 	var updated model.Conversation
 	require.NoError(t, db.First(&updated, conversation.ID).Error)
+	require.NotNil(t, updated.AssigneeID, "最终会话必须已分配")
 	require.Equal(t, agent.ID, *updated.AssigneeID)
-	rateCount, err := NewRateLimiter(rdb).GetCount(context.Background(), inbox.ID, agent.ID, 300)
+	rateKeys, err := rdb.Keys(context.Background(), fmt.Sprintf("%s%d:%d:*", rateLimitKeyPrefix, inbox.ID, agent.ID)).Result()
 	require.NoError(t, err)
+	rateCount := 0
+	for _, key := range rateKeys {
+		count, err := rdb.Get(context.Background(), key).Int()
+		require.NoError(t, err)
+		rateCount += count
+	}
 	require.Equal(t, 1, rateCount, "the CAS loser must not increment the rate-limit key")
 }