import uuid
from typing import Annotated

from fastapi import Header


async def get_session_id(x_session_id: Annotated[str | None, Header()] = None) -> str:
    """
    Return the session ID from the X-Session-Id header.
    If the header is absent, generate a fresh UUID so every resource
    is still scoped to *some* session.
    """
    return x_session_id or str(uuid.uuid4())