// Simplified transaction flow
tx, _ := db.Begin()

// Debit sender
tx.Exec("UPDATE accounts SET balance = balance - $1 WHERE user_id = $2", amount, senderID)

// Credit recipient  
tx.Exec("UPDATE accounts SET balance = balance + $1 WHERE user_id = $2", amount, recipientID)

// Insert transaction record
tx.Exec("INSERT INTO transactions (...) VALUES (...)")

// Insert audit log
tx.Exec("INSERT INTO audit_log (...) VALUES (...)")

tx.Commit()

message PaymentRequest {
  string request_id = 1;  // Client-provided unique ID
  string user_id = 2;
  string recipient_id = 3;
  int64 amount = 4;
  string currency = 5;
}

CREATE TABLE accounts (
  id TEXT PRIMARY KEY,
  user_id TEXT NOT NULL,
  currency TEXT NOT NULL,
  balance BIGINT NOT NULL DEFAULT 0,
  created_at TIMESTAMP,
  updated_at TIMESTAMP,
  UNIQUE(user_id, currency)
);

docker compose up -d --build wallet-core

cd wallet-core
go build -o wallet-core ./cmd/server
./wallet-core -config config.yaml

grpcurl -plaintext localhost:50051 wallet.WalletService/HealthCheck

wallet-core/
├── cmd/
│   ├── server/
│   │   └── main.go       # Entry point
│   └── tools/            # CLI utilities
├── internal/
│   ├── config/           # Configuration loading
│   ├── database/         # DB connection & migrations
│   ├── ledger/           # Core transaction engine
│   ├── models/           # Domain models
│   ├── repository/       # Data access layer
│   ├── server/           # gRPC server adapters
│   └── services/         # Business logic (16 services)
├── pkg/                  # Shared packages
├── config.yaml           # Default configuration
└── Dockerfile