Function assert_can_write 

pub async fn assert_can_write(
    db: &SqlitePool,
    current_user: Uuid,
    destination: Destination,
) -> Result<(), Error>

Verify that the calling user is allowed to write to the given destination. Personal scope is always allowed; group scope requires owner membership.

Errors

Returns Error::Forbidden if the user is not an owner of the target group, Error::NotFound if the group does not exist.