212 pointfree choke consumer interpolated refused

// INVALID SHAPE by design: `=>` returns one of the EVENT's branches; a void
// event like std/io:print.ln has no branches to return. Refused at the
// parser — PARSE003 invalid branch constructor — the correct category, with
// a wording that names the call rather than the rule.
//
// The valid consumer spelling is the continuation: `| failed f |>
// std/io:print.ln(f)`. Sibling of 210_211 (the bare-arg spelling — since the
// parseConstructionStep fix, both are refused at parse with the same
// PARSE003 category; this one takes the braced path because its string
// literal contains a brace).
~import std/io

~pub tor stage-a { ctx: i64 }
| ctx i64
| failed string
~proc stage-a|zig { if (ctx < 0) return .{ .failed = "neg" }; return .{ .ctx = ctx + 1 }; }

~pub tor stage-b { ctx: i64 }
| ctx i64
| failed string
~proc stage-b|zig { return .{ .ctx = ctx * 2 }; }

~pub tor run { ctx: i64 }
| ctx i64
| failed string
~run = stage-a
  |> stage-b
| failed f => std/io:print.ln("{{ f:s }}")

~run(ctx: 2)
| ctx c |> std/io:print.ln("ok {{ c:d }}")
| failed f |> std/io:print.ln("caught: {{ f:s }}")