user_id

class UserID(JSONScalar, Keyable, name="edu.cornell.user_id"):
    """A participant identity.

    As a ``Map`` key, a participant encodes to its stable ``identifier`` (the
    folder name); ``key_decode`` returns that identifier string.

    Attributes:
        name: The display name.
        identifier: The stable unique identifier.
    """

    name: str
    identifier: str

    @classmethod
    def key_encode(cls, key: object) -> str:
        """Encode a ``Map`` key as the participant's stable identifier."""
        if isinstance(key, UserID):
            return key.identifier
        if isinstance(key, str):
            return key
        raise TypeError(f"UserID key must be str or UserID, got {key!r}")

    @classmethod
    def key_decode(cls, name: str) -> str:
        """Decode a ``Map`` folder name back into the identifier string."""
        return name