app\models\base.py

import uuid
from datetime import datetime, timezone
from sqlalchemy import DateTime, String
from sqlalchemy.orm import DeclarativeBase, Mapped, mapped_column

class Base(DeclarativeBase):
    """
    Standard SQLAlchemy 2.0 Declarative Base.
    All models in the application must inherit from this [cite: 1, 166-167, 211].
    """
    pass

class UUIDMixin:
    """Provides a standard UUID primary key for models[cite: 1, 211]."""
    id: Mapped[str] = mapped_column(
        String(64), 
        primary_key=True, 
        default=lambda: uuid.uuid4().hex
    )

class TimestampMixin:
    """Provides standard created_at and updated_at timestamps[cite: 1, 211]."""
    created_at: Mapped[datetime] = mapped_column(
        DateTime(timezone=True), 
        default=lambda: datetime.now(timezone.utc)
    )
    updated_at: Mapped[datetime] = mapped_column(
        DateTime(timezone=True), 
        default=lambda: datetime.now(timezone.utc), 
        onupdate=lambda: datetime.now(timezone.utc)
    )