WIP checkpoint: Wallet & ledger models + Alembic migration (wallets, transactions)

backend/app/models/__init__.py

@@ -2,5 +2,14 @@ from app.models.user import User
 from app.models.session import Session
 from app.models.world import World
 from app.models.asset import Asset
+from app.models.wallet import Transaction, TransactionType, Wallet
 
-__all__ = ["User", "Session", "World", "Asset"]
+__all__ = [
+    "User",
+    "Session",
+    "World",
+    "Asset",
+    "Wallet",
+    "Transaction",
+    "TransactionType",
+]

backend/app/models/wallet.py

@@ -0,0 +1,73 @@
+"""Wallet and transaction ledger models."""
+
+import enum
+
+from sqlalchemy import (
+    BigInteger,
+    CheckConstraint,
+    Column,
+    DateTime,
+    ForeignKey,
+    Integer,
+    Text,
+)
+from sqlalchemy.dialects.postgresql import ENUM, JSONB
+from sqlalchemy.sql import func
+
+from app.database import Base
+
+
+class TransactionType(str, enum.Enum):
+    CREDIT_PURCHASE = "credit_purchase"
+    MARKETPLACE_PURCHASE = "marketplace_purchase"
+    MARKETPLACE_SALE = "marketplace_sale"
+    ESCROW_RELEASE = "escrow_release"
+    PAYOUT = "payout"
+    REFUND = "refund"
+    ADMIN_ADJUSTMENT = "admin_adjustment"
+
+
+class Wallet(Base):
+    __tablename__ = "wallets"
+    __table_args__ = (
+        CheckConstraint("balance >= 0", name="ck_wallets_balance_nonnegative"),
+    )
+
+    id = Column(BigInteger, primary_key=True, index=True)
+    user_id = Column(
+        Integer,
+        ForeignKey("users.id", ondelete="CASCADE"),
+        unique=True,
+        index=True,
+        nullable=False,
+    )
+    balance = Column(BigInteger, nullable=False, default=0, server_default="0")
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+    updated_at = Column(
+        DateTime(timezone=True), server_default=func.now(), onupdate=func.now()
+    )
+
+
+class Transaction(Base):
+    __tablename__ = "transactions"
+
+    id = Column(BigInteger, primary_key=True, index=True)
+    wallet_id = Column(
+        BigInteger, ForeignKey("wallets.id"), nullable=False
+    )
+    type = Column(
+        ENUM(
+            TransactionType,
+            name="transaction_type",
+            create_type=False,
+            values_callable=lambda enum_cls: [member.value for member in enum_cls],
+        ),
+        nullable=False,
+    )
+    amount = Column(BigInteger, nullable=False)
+    balance_after = Column(BigInteger, nullable=False)
+    reference_type = Column(Text, nullable=True)
+    reference_id = Column(Text, nullable=True)
+    idempotency_key = Column(Text, unique=True, index=True, nullable=True)
+    metadata_json = Column(JSONB, nullable=True)
+    created_at = Column(DateTime(timezone=True), server_default=func.now())