fix(gacha): validate reward pool before charging currency (#175)

Filter out gacha entries with no items at the query level (EXISTS
subquery) and reorder Play methods to validate the pool before
calling transact(), so players are never charged for a misconfigured
gacha.

server/channelserver/handlers_gacha_test.go

@@ -186,7 +186,10 @@ func TestHandleMsgMhfReceiveGachaItem_Freeze(t *testing.T) {
 
 func TestHandleMsgMhfPlayNormalGacha_TransactError(t *testing.T) {
 	server := createMockServer()
-	gachaRepo := &mockGachaRepo{txErr: errors.New("transact failed")}
+	gachaRepo := &mockGachaRepo{
+		txErr:      errors.New("transact failed"),
+		rewardPool: []GachaEntry{{ID: 10, Weight: 100}},
+	}
 	server.gachaRepo = gachaRepo
 	server.userRepo = &mockUserRepoGacha{}
 	ensureGachaService(server)
@@ -269,7 +272,10 @@ func TestHandleMsgMhfPlayNormalGacha_Success(t *testing.T) {
 
 func TestHandleMsgMhfPlayStepupGacha_TransactError(t *testing.T) {
 	server := createMockServer()
-	gachaRepo := &mockGachaRepo{txErr: errors.New("transact failed")}
+	gachaRepo := &mockGachaRepo{
+		txErr:      errors.New("transact failed"),
+		rewardPool: []GachaEntry{{ID: 10, Weight: 100}},
+	}
 	server.gachaRepo = gachaRepo
 	server.userRepo = &mockUserRepoGacha{}
 	ensureGachaService(server)
@@ -473,7 +479,10 @@ func TestHandleMsgMhfGetBoxGachaInfo_Success(t *testing.T) {
 
 func TestHandleMsgMhfPlayBoxGacha_TransactError(t *testing.T) {
 	server := createMockServer()
-	gachaRepo := &mockGachaRepo{txErr: errors.New("transact failed")}
+	gachaRepo := &mockGachaRepo{
+		txErr:      errors.New("transact failed"),
+		rewardPool: []GachaEntry{{ID: 10, Weight: 100}},
+	}
 	server.gachaRepo = gachaRepo
 	server.userRepo = &mockUserRepoGacha{}
 	ensureGachaService(server)

server/channelserver/repo_gacha.go

@@ -29,10 +29,14 @@ func (r *GachaRepository) GetEntryForTransaction(gachaID uint32, rollID uint8) (
 }
 
 // GetRewardPool returns the entry_type=100 reward pool for a gacha, ordered by weight descending.
+// Entries with no corresponding items in gacha_items are excluded.
 func (r *GachaRepository) GetRewardPool(gachaID uint32) ([]GachaEntry, error) {
 	var entries []GachaEntry
 	rows, err := r.db.Queryx(
-		`SELECT id, weight, rarity FROM gacha_entries WHERE gacha_id = $1 AND entry_type = 100 ORDER BY weight DESC`,
+		`SELECT e.id, e.weight, e.rarity FROM gacha_entries e
+		 WHERE e.gacha_id = $1 AND e.entry_type = 100
+		   AND EXISTS (SELECT 1 FROM gacha_items gi WHERE gi.entry_id = e.id)
+		 ORDER BY e.weight DESC`,
 		gachaID,
 	)
 	if err != nil {

server/channelserver/svc_gacha.go

@@ -164,14 +164,17 @@ func rewardsToItems(rewards []GachaReward) []GachaItem {
 	return items
 }
 
-// PlayNormalGacha processes a normal gacha roll: deducts cost, selects random
-// rewards, saves items, and returns the result.
+// PlayNormalGacha processes a normal gacha roll: validates the reward pool,
+// deducts cost, selects random rewards, saves items, and returns the result.
 func (svc *GachaService) PlayNormalGacha(userID, charID, gachaID uint32, rollType uint8) (*GachaPlayResult, error) {
-	rolls, err := svc.transact(userID, charID, gachaID, rollType)
+	entries, err := svc.gachaRepo.GetRewardPool(gachaID)
 	if err != nil {
 		return nil, err
 	}
-	entries, err := svc.gachaRepo.GetRewardPool(gachaID)
+	if len(entries) == 0 {
+		return nil, errors.New("gacha has no valid reward entries")
+	}
+	rolls, err := svc.transact(userID, charID, gachaID, rollType)
 	if err != nil {
 		return nil, err
 	}
@@ -180,9 +183,17 @@ func (svc *GachaService) PlayNormalGacha(userID, charID, gachaID uint32, rollTyp
 	return &GachaPlayResult{Rewards: rewards}, nil
 }
 
-// PlayStepupGacha processes a stepup gacha roll: deducts cost, advances step,
-// awards frontier points, selects random + guaranteed rewards, and saves items.
+// PlayStepupGacha processes a stepup gacha roll: validates the reward pool,
+// deducts cost, advances step, awards frontier points, selects random +
+// guaranteed rewards, and saves items.
 func (svc *GachaService) PlayStepupGacha(userID, charID, gachaID uint32, rollType uint8) (*StepupPlayResult, error) {
+	entries, err := svc.gachaRepo.GetRewardPool(gachaID)
+	if err != nil {
+		return nil, err
+	}
+	if len(entries) == 0 {
+		return nil, errors.New("gacha has no valid reward entries")
+	}
 	rolls, err := svc.transact(userID, charID, gachaID, rollType)
 	if err != nil {
 		return nil, err
@@ -197,11 +208,6 @@ func (svc *GachaService) PlayStepupGacha(userID, charID, gachaID uint32, rollTyp
 		svc.logger.Error("Failed to insert gacha stepup state", zap.Error(err))
 	}
 
-	entries, err := svc.gachaRepo.GetRewardPool(gachaID)
-	if err != nil {
-		return nil, err
-	}
-
 	guaranteedItems, _ := svc.gachaRepo.GetGuaranteedItems(rollType, gachaID)
 	randomRewards := svc.resolveRewards(entries, rolls, false)
 
@@ -223,14 +229,18 @@ func (svc *GachaService) PlayStepupGacha(userID, charID, gachaID uint32, rollTyp
 	}, nil
 }
 
-// PlayBoxGacha processes a box gacha roll: deducts cost, selects random entries
-// without replacement, records drawn entries, saves items, and returns the result.
+// PlayBoxGacha processes a box gacha roll: validates the reward pool, deducts
+// cost, selects random entries without replacement, records drawn entries,
+// saves items, and returns the result.
 func (svc *GachaService) PlayBoxGacha(userID, charID, gachaID uint32, rollType uint8) (*GachaPlayResult, error) {
-	rolls, err := svc.transact(userID, charID, gachaID, rollType)
+	entries, err := svc.gachaRepo.GetRewardPool(gachaID)
 	if err != nil {
 		return nil, err
 	}
-	entries, err := svc.gachaRepo.GetRewardPool(gachaID)
+	if len(entries) == 0 {
+		return nil, errors.New("gacha has no valid reward entries")
+	}
+	rolls, err := svc.transact(userID, charID, gachaID, rollType)
 	if err != nil {
 		return nil, err
 	}

server/channelserver/svc_gacha_test.go

@@ -27,6 +27,7 @@ func TestGachaService_PlayNormalGacha(t *testing.T) {
 	}{
 		{
 			name:    "transact error",
+			pool:    []GachaEntry{{ID: 10, Weight: 100}},
 			txErr:   errors.New("tx fail"),
 			wantErr: true,
 		},
@@ -36,6 +37,10 @@ func TestGachaService_PlayNormalGacha(t *testing.T) {
 			poolErr: errors.New("pool fail"),
 			wantErr: true,
 		},
+		{
+			name:    "empty reward pool",
+			wantErr: true,
+		},
 		{
 			name:    "success single roll",
 			txRolls: 1,
@@ -95,6 +100,7 @@ func TestGachaService_PlayStepupGacha(t *testing.T) {
 	}{
 		{
 			name:    "transact error",
+			pool:    []GachaEntry{{ID: 10, Weight: 100}},
 			txErr:   errors.New("tx fail"),
 			wantErr: true,
 		},
@@ -104,6 +110,10 @@ func TestGachaService_PlayStepupGacha(t *testing.T) {
 			poolErr: errors.New("pool fail"),
 			wantErr: true,
 		},
+		{
+			name:    "empty reward pool",
+			wantErr: true,
+		},
 		{
 			name:    "success with guaranteed",
 			txRolls: 1,