080 effect branch phantom payload

// Test: effect branch with phantom-stated payload (smoke test).
//
// Producer yields `frame(f)` where `f: *Frame[ready]` — a pointer carrying
// a phantom state annotation. Consumer handles each frame and reads its
// id. The phantom state `[ready]` is currently decorative at the Koru
// level (Phase 4 hasn't extended the phantom checker to track obligations
// through effect branches). This test verifies the SURFACE works — that
// `!` payloads can carry phantom annotations and the lowering preserves
// the pointer type cleanly.

~import "$std/io"

const std = @import("std");

const Frame = struct { id: i32 };

~pub event frames { n: usize }
! frame *Frame[ready]

~proc frames|zig {
    var i: usize = 0;
    while (i < n) : (i += 1) {
        const f = std.heap.page_allocator.create(Frame) catch unreachable;
        f.* = Frame{ .id = @intCast(i) };
        frame(f);
        std.heap.page_allocator.destroy(f);
    }
}

~frames(n: 3)
! frame f |> std.io:print.blk {
    frame id={{ f.id:d }}
}