039 effect discard sibling illegal

// RULING 3: a no-op `_` body on an effect branch is ILLEGAL when the branch
// is already handled by a sibling — `! row _ |> _` discards nothing. Effects
// are per-fire filters: an unmatched fire is a no-op by nature, so the
// discard borrows `|`-branch exhaustiveness intuition where none applies —
// and reads like it catches "the other rows", which it does not.
//
// Stays legal: `|` outcome discards (a result must route somewhere — and
// KORU050 can require the unguarded arm), a LONE `! row _ |> _` on a
// REQUIRED effect (explicit handle-and-ignore — RULING 1's carve-out), and
// `! row _ |> <action>` (discards the payload but actually acts).

~import std/io

~pub tor poll { x: i64 }
! row i64
| done

~proc poll|zig { return .{ .done = .{} }; }

~poll(x: 1)
! row r when r > 10 |> std/io:print.ln("big")
! row _ |> _
| done |> _