feat: 보상 재시도 + TX 확정 대기 + 에러 포맷 통일 + 품질 고도화

- 보상 지급 실패 시 즉시 재시도(3회 backoff) + DB 기록 + 백그라운드 워커 재시도
- WaitForTx 폴링으로 블록체인 TX 확정 대기, SendTxAndWait 편의 메서드
- chain 트랜잭션 코드 중복 제거 (userTx/operatorTx 헬퍼, 50% 감소)
- AppError 기반 에러 응답 포맷 통일 (8개 코드, 전 핸들러 마이그레이션)
- TX 에러 분류 + 한국어 사용자 메시지 매핑 (11가지 패턴)
- player 서비스 테스트 20개 + chain WaitForTx 테스트 10개 추가

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/bossraid/service.go

@@ -208,17 +208,21 @@ func (s *Service) CompleteRaid(sessionName string, rewards []PlayerReward) (*Bos
 		return nil, nil, fmt.Errorf("방을 찾을 수 없습니다: %w", err)
 	}
 
-	// Grant rewards outside the transaction to avoid holding the lock during RPC calls
+	// Grant rewards outside the transaction to avoid holding the lock during RPC calls.
+	// Each reward is attempted up to 3 times with exponential backoff before being
+	// recorded as a RewardFailure for background retry.
 	resultRewards = make([]RewardResult, 0, len(rewards))
 	hasRewardFailure := false
 	if s.rewardGrant != nil {
 		for _, r := range rewards {
-			grantErr := s.rewardGrant(r.Username, r.TokenAmount, r.Assets)
+			grantErr := s.grantWithRetry(r.Username, r.TokenAmount, r.Assets)
 			result := RewardResult{Username: r.Username, Success: grantErr == nil}
 			if grantErr != nil {
 				result.Error = grantErr.Error()
-				log.Printf("보상 지급 실패: %s: %v", r.Username, grantErr)
+				log.Printf("보상 지급 실패 (재시도 소진): %s: %v", r.Username, grantErr)
 				hasRewardFailure = true
+				// 실패한 보상을 DB에 기록하여 백그라운드 재시도 가능하게 함
+				s.saveRewardFailure(sessionName, r, grantErr)
 			}
 			resultRewards = append(resultRewards, result)
 		}
@@ -231,12 +235,18 @@ func (s *Service) CompleteRaid(sessionName string, rewards []PlayerReward) (*Bos
 		}
 	}
 
-	// Grant experience to players
+	// Grant experience to players (with retry)
 	if s.expGrant != nil {
 		for _, r := range rewards {
 			if r.Experience > 0 {
-				if expErr := s.expGrant(r.Username, r.Experience); expErr != nil {
-					log.Printf("경험치 지급 실패: %s: %v", r.Username, expErr)
+				expErr := s.grantExpWithRetry(r.Username, r.Experience)
+				if expErr != nil {
+					log.Printf("경험치 지급 실패 (재시도 소진): %s: %v", r.Username, expErr)
+					// 경험치 실패도 RewardFailure에 기록 (토큰/에셋 없이 경험치만)
+					s.saveRewardFailure(sessionName, PlayerReward{
+						Username:   r.Username,
+						Experience: r.Experience,
+					}, expErr)
 				}
 			}
 		}
@@ -473,3 +483,62 @@ func (s *Service) GetServerStatus(serverName string) (*DedicatedServer, []RoomSl
 	}
 	return server, slots, nil
 }
+
+// --- Reward retry helpers ---
+
+const immediateRetries = 3
+
+// grantWithRetry attempts the reward grant up to 3 times with backoff (1s, 2s).
+func (s *Service) grantWithRetry(username string, tokenAmount uint64, assets []core.MintAssetPayload) error {
+	delays := []time.Duration{1 * time.Second, 2 * time.Second}
+	var lastErr error
+	for attempt := 0; attempt < immediateRetries; attempt++ {
+		lastErr = s.rewardGrant(username, tokenAmount, assets)
+		if lastErr == nil {
+			return nil
+		}
+		if attempt < len(delays) {
+			log.Printf("보상 지급 재시도 (%d/%d): %s: %v", attempt+1, immediateRetries, username, lastErr)
+			time.Sleep(delays[attempt])
+		}
+	}
+	return lastErr
+}
+
+// grantExpWithRetry attempts the experience grant up to 3 times with backoff (1s, 2s).
+func (s *Service) grantExpWithRetry(username string, exp int) error {
+	delays := []time.Duration{1 * time.Second, 2 * time.Second}
+	var lastErr error
+	for attempt := 0; attempt < immediateRetries; attempt++ {
+		lastErr = s.expGrant(username, exp)
+		if lastErr == nil {
+			return nil
+		}
+		if attempt < len(delays) {
+			log.Printf("경험치 지급 재시도 (%d/%d): %s: %v", attempt+1, immediateRetries, username, lastErr)
+			time.Sleep(delays[attempt])
+		}
+	}
+	return lastErr
+}
+
+// saveRewardFailure records a failed reward in the DB for background retry.
+func (s *Service) saveRewardFailure(sessionName string, r PlayerReward, grantErr error) {
+	assets := "[]"
+	if len(r.Assets) > 0 {
+		if data, err := json.Marshal(r.Assets); err == nil {
+			assets = string(data)
+		}
+	}
+	rf := &RewardFailure{
+		SessionName: sessionName,
+		Username:    r.Username,
+		TokenAmount: r.TokenAmount,
+		Assets:      assets,
+		Experience:  r.Experience,
+		Error:       grantErr.Error(),
+	}
+	if err := s.repo.SaveRewardFailure(rf); err != nil {
+		log.Printf("보상 실패 기록 저장 실패: %s/%s: %v", sessionName, r.Username, err)
+	}
+}