168 effect inliner guarded branch drops prelude

// 400_168: a GUARDED-ONLY effect branch (`! beep n when n > 3`, no catch-all
// `! beep _`) composes with sibling YIELDING optional arms through the inline
// cut-1 splice — because a yielding arm is invoked by DIRECT CALL.
//
// HISTORY: this pinned the guarded-branch-drops-prelude bug. A guarded-only
// consumer made the event inline-eligible, and the inline splice bound no
// callable for the body's `if (tick) |f| f()` (the nullable-fn-ptr form) —
// leaking a raw Zig `undeclared identifier 'tick'`.
//
// RESOLUTION (ruled 2026-07-19, Option B): a YIELDING optional arm is a
// callable, invoked directly (`tick()`, `beep(7)`); an omitted handler is a
// producer-side no-op that optimizes away. One contract across both lowerings —
// the body's spelling no longer depends on which path the consumer's branch
// shape picks. (Only a RESUMING arm `-> T` stays nullable: 400_148.) So this
// body inlines cleanly, and the guarded-only consumer arm splices as-is.
~import std/io

~pub tor run {}
! ?tick
! ?beep i64
| done i64

~proc run|zig {
    tick();
    beep(7);
    return .{ .done = 99 };
}

~run()
! tick |> std/io:print.ln("tick")
! beep n when n > 3 |> std/io:print.ln("beep {{ n:d }}")
| done r |> std/io:print.ln("done {{ r:d }}")