Function prelude 

pub fn prelude(
    schema: &str,
    role: Option<&str>,
    scope: Scope,
    statement_timeout: Duration,
) -> String

What a guest’s statements run under: the schema is written as every statement writes it (folded_ident), so the path a guest’s SQL resolves in, the schema a deploy created and the one a migration ran in are the same schema. role is the one a session imposes on its connection, where it does.