023 pipeline chain depth

// TEST: Parser bug — three-level |> chain with Source body fails
//
// Pattern (kernel-style but simplified):
//   | branch |>
//       event_a(0..N)
//       |> event_b { multi-line source }
//       |> event_c { source }
//   | other_branch |>
//       ...
//
// Parser error: branch '' has 2 continuations without 'when'
// This blocks: step(N) |> pairwise { } |> self { }

~import std/kernel
~import std/io

~std/kernel:shape(Body) {
    mass: f64,
}

~std/kernel:init(Body) {
    { mass: 1.0 },
    { mass: 2.0 },
}
| kernel k |> std/kernel:step(0..3)
    | step |> std/kernel:pairwise { k.mass += k.other.mass * 0.0 } |> std/kernel:self { k.mass += 0.1 }
| computed c |> std/io:print.blk {
        mass[0]={{ c[0].mass:f }}
    }