diff --git a/.forge/SPRING-ARC-SEQUENCE-attempt-1-run-a74343256c06.md b/.forge/SPRING-ARC-SEQUENCE-attempt-1-run-a74343256c06.md
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+# SPRING-ARC-SEQUENCE-attempt-1-run-a74343256c06
+
+Forge 이슈 작업 브랜치 `forge/SPRING-ARC-SEQUENCE-attempt-1-run-a74343256c06`.
diff --git a/docs/architecture/transaction-sequence.md b/docs/architecture/transaction-sequence.md
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+```mermaid
+sequenceDiagram
+    participant User as User
+    participant Controller as Controller
+    participant PaymentService as PaymentService
+    participant Gateway as PaymentGateway
+    participant DB as Database
+
+    User ->> Controller: Initiate Payment
+    Controller ->> PaymentService: Process Payment
+    PaymentService ->> Gateway: Call Payment Gateway
+    alt Successful Payment
+        Gateway -->> PaymentService: Payment Success
+        PaymentService ->> DB: Save Transaction
+        DB -->> PaymentService: Transaction Saved
+        PaymentService -->> Controller: Payment Processed
+        Controller -->> User: Payment Successful
+    else External Gateway Failure
+        Gateway -->> PaymentService: Payment Failed
+        PaymentService -->> Controller: Payment Failed
+        Controller -->> User: Payment Failed
+    else DB Failure
+        Gateway -->> PaymentService: Payment Success
+        PaymentService ->> DB: Save Transaction
+        DB -->> PaymentService: DB Error
+        PaymentService ->> Controller: Rollback Transaction
+        Controller -->> User: Payment Failed
+    end
+```
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