Koru Standard Library: the `fold` part of supervisor.kz — the elaboration itself: the `supervised` transform decl+proc and the generated-AST constructors it builds the step tor and `#`/`@` fold from. Joined via `~part fold` in supervisor.kz; merged into the supervisor module at load. `std`/`ast`/`H`/`functional` arrive at module scope from the other parts — local imports here would shadow them.

~[keyword|comptime|transform] pub tor supervised {
    source: Source,
    invocation: *const Invocation,
    item: std/compiler:*const Item,
    program: std/compiler:*const Program,
    reporter: std/compiler:*ErrorReporter,
    allocator: std.mem.Allocator
} -> SiteResult