"""Shared FastAPI dependencies — DB session per request."""
from __future__ import annotations

from collections.abc import AsyncIterator

from fastapi import Request
from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker


async def get_session(request: Request) -> AsyncIterator[AsyncSession]:
    """Yield an AsyncSession bound to the engine on app.state.

    The engine + session factory are wired up in `app.lifespan`. Tests
    swap them out via dependency_overrides.
    """
    factory: async_sessionmaker[AsyncSession] = request.app.state.session_factory
    async with factory() as session:
        yield session