148 effect proc optional resume nullable alias

// OPTIONAL RESUME ARMS, proc side — designed 2026-07-03. A `proc |zig` impl
// gets the presence truth as a NULLABLE FUNCTION POINTER alias: for an
// optional arm the emitter binds
//     const ask: ?*const fn (...) T = if (@hasDecl(__H, "ask")) &__H.ask else null;
// instead of today's synthesized no-op (which is invalid Zig for any
// value-resuming arm, and poisons @hasDecl for all of them). The proc then
// writes idiomatic Zig: `if (ask) |f| ...` — comptime-known null, folds away.
//
// This consumer OMITS the handler, so the unwrap fails and the proc's own
// explicit fallback wins: prints 0.
~import std/io

~pub tor query { q: i64 }
! ?ask i64 -> i64
| done i64

~proc query|zig {
    if (ask) |f| {
        return .{ .done = f(q) };
    }
    return .{ .done = 0 };
}

~query(q: 41)
| done r |> std/io:print.ln("{{ r:d }}")