diff --git a/.forge/iss-6f8eac22f6f0-attempt-1.md b/.forge/iss-6f8eac22f6f0-attempt-1.md
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+# iss-6f8eac22f6f0-attempt-1
+
+Forge 이슈 작업 브랜치 `forge/iss-6f8eac22f6f0-attempt-1`.
diff --git a/docs/architecture/transaction-sequence.md b/docs/architecture/transaction-sequence.md
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+```mermaid
+sequenceDiagram
+    participant User
+    participant PaymentService
+    participant PaymentGateway
+    participant Database
+
+    %% 정상 흐름
+    User->>PaymentService: 결제 요청
+    PaymentService->>Database: 거래 데이터 저장
+    Database-->>PaymentService: 저장 완료
+    PaymentService->>PaymentGateway: 결제 요청
+    PaymentGateway-->>PaymentService: 결제 성공
+    PaymentService->>Database: 거래 완료 상태 업데이트
+    Database-->>PaymentService: 상태 업데이트 완료
+    PaymentService-->>User: 결제 성공 응답
+
+    %% 외부 실패 흐름
+    User->>PaymentService: 결제 요청
+    PaymentService->>Database: 거래 데이터 저장
+    Database-->>PaymentService: 저장 완료
+    PaymentService->>PaymentGateway: 결제 요청
+    PaymentGateway-->>PaymentService: 결제 실패
+    PaymentService->>Database: 거래 실패 상태 업데이트
+    Database-->>PaymentService: 상태 업데이트 완료
+    PaymentService-->>User: 결제 실패 응답
+
+    %% DB 실패 흐름
+    User->>PaymentService: 결제 요청
+    PaymentService->>Database: 거래 데이터 저장
+    Database-->>PaymentService: 저장 실패
+    PaymentService-->>User: 결제 실패 응답
+
+    %% commit 흐름
+    PaymentService->>Database: 커밋
+    Database-->>PaymentService: 커밋 완료
+
+    %% rollback 흐름
+    PaymentService->>Database: 롤백
+    Database-->>PaymentService: 롤백 완료
+```
\ No newline at end of file