docs/architecture/transaction-sequence.md

@@ -0,0 +1,24 @@
+```mermaid
+sequenceDiagram
+    participant User
+    participant PaymentGateway
+    participant Application
+    participant Database
+    User->>Application: Initiate Payment
+    Application->>PaymentGateway: Process Payment
+    alt Successful Payment
+        PaymentGateway-->>Application: Payment Approved
+        Application->>Database: Commit Transaction
+        Database-->>Application: Transaction Committed
+        Application-->>User: Payment Successful
+    else External Failure
+        PaymentGateway-->>Application: Payment Error
+        Application-->>User: Payment Failed
+    else DB Failure
+        Application->>Database: Attempt Transaction
+        Database-->>Application: Transaction Error
+        Application->>Database: Rollback Transaction
+        Database-->>Application: Transaction Rolled Back
+        Application-->>User: Payment Failed
+    end
+```