fix: require balance for automatic task claims

internal/store/tasks.go

@@ -205,7 +205,7 @@ func (s *Store) ClaimTask(ctx context.Context, input ClaimTaskInput) (*TaskOrder
 	if wallet.Status != 1 {
 		return nil, ErrAccountRestricted
 	}
-	if member.AutoDispatch == 1 && wallet.AvailableAmount < input.MinimumAmount {
+	if member.AutoDispatch == 1 && (wallet.AvailableAmount <= 0 || wallet.AvailableAmount < input.MinimumAmount) {
 		return nil, ErrInsufficientBalance
 	}
 	var pending int64

internal/tasks/service.go

@@ -206,7 +206,7 @@ func (s *Service) Eligibility(ctx context.Context, tenantID, memberID, hallID in
 		result.reject("LEVEL_NOT_ELIGIBLE", "当前等级不能进入该任务大厅")
 	case row.WalletStatus != 1:
 		result.reject("ACCOUNT_RESTRICTED", "账户状态受限")
-	case row.AutoDispatch == 1 && row.AvailableAmount < policy.MinimumAmount:
+	case row.AutoDispatch == 1 && (row.AvailableAmount <= 0 || row.AvailableAmount < policy.MinimumAmount):
 		result.reject("INSUFFICIENT_BALANCE", "可用余额不足")
 	case row.DailyLimit > 0 && row.TodayCount >= row.DailyLimit:
 		result.reject("DAILY_LIMIT_REACHED", "已达当日领取上限")

internal/tasks/service_test.go

@@ -92,6 +92,21 @@ func TestEligibilityAllowsManualDispatchBelowMinimumBalance(t *testing.T) {
 	}
 }
 
+func TestEligibilityRejectsAutoDispatchWithZeroBalanceWhenMinimumIsZero(t *testing.T) {
+	repository := &fakeRepository{config: json.RawMessage(`{"features":{"task_enabled":true},"task_minimum_amount":0,"task_business_start_at":"09:00","task_business_end_at":"22:00"}`),
+		eligibility: &store.TaskEligibility{MemberStatus: 1, AutoDispatch: 1, HallEligible: true, AvailableAmount: 0, WalletStatus: 1, DailyLimit: 5}}
+	service := New(repository)
+	service.now = func() time.Time { return time.Date(2026, 10, 9, 10, 0, 0, 0, shanghai) }
+
+	result, err := service.Eligibility(context.Background(), 0, 10, 1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if result.Eligible || result.Reason != "INSUFFICIENT_BALANCE" {
+		t.Fatalf("zero balance must not allow automatic claiming: %#v", result)
+	}
+}
+
 func TestClaimFailsClosedWithoutTaskSwitch(t *testing.T) {
 	repository := &fakeRepository{config: json.RawMessage(`{}`)}
 	service := New(repository)