.forge/iss-5a912ed79baf-attempt-1.md

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+# iss-5a912ed79baf-attempt-1
+
+Forge 이슈 작업 브랜치 `forge/iss-5a912ed79baf-attempt-1`.

docs/architecture/transaction-sequence.md

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+```mermaid
+sequenceDiagram
+    participant User as 유저
+    participant PaymentService as 결제 서비스
+    participant PaymentGateway as 결제 게이트웨이
+    participant Database as 데이터베이스
+
+    User->>PaymentService: 결제 요청
+    PaymentService->>Database: 결제 정보 저장
+    activate Database
+    Database-->>PaymentService: 저장 완료
+    deactivate Database
+
+    alt 정상 흐름
+        PaymentService->>PaymentGateway: 결제 요청
+        activate PaymentGateway
+        PaymentGateway-->>PaymentService: 결제 성공
+        deactivate PaymentGateway
+        PaymentService->>User: 결제 완료
+
+    else 외부 실패
+        PaymentService->>PaymentGateway: 결제 요청
+        activate PaymentGateway
+        PaymentGateway-->>PaymentService: 결제 실패
+        deactivate PaymentGateway
+        PaymentService->>Database: 롤백
+        activate Database
+        Database-->>PaymentService: 롤백 완료
+        deactivate Database
+        PaymentService->>User: 결제 실패
+    end
+
+    else DB 실패
+        PaymentService->>Database: 결제 정보 저장
+        activate Database
+        Database-->>PaymentService: 저장 실패
+        deactivate Database
+        PaymentService->>User: 저장 실패
+    end
+```