211 event arm join discharges once

// PINS: the join after a non-keyword tor's arms discharges an obligation
// live across the call exactly once — 400_193 pins this for `if`, here the
// armed step is a plain proc tor `pick`. `r` is live-through both arms and
// drops once at the join; the arm-local `q` discharges at the hit arm's leaf.

~import std/io
const std = @import("std");

const Res = struct { v: i32 };

~tor grab { v: i64 } -> *Res<held!>
~proc grab|zig {
    const r = std.heap.page_allocator.create(Res) catch unreachable;
    r.* = .{ .v = @intCast(v) };
    return r;
}

~tor drop { r: *Res<!held> }
~proc drop|zig {
    std.debug.print("drop {d}\n", .{r.v});
    std.heap.page_allocator.destroy(r);
}

~tor readv { r: *Res<held> } -> i64
~proc readv|zig {
    return r.v;
}

~tor pick {}
| hit
| miss
~proc pick|zig {
    return .{ .hit = .{} };
}

~tor doit {}
| ok
| fail
~proc doit|zig {
    return .{ .ok = .{} };
}

~grab(v: 7): r |> doit()
| ok |> std/io:print.ln("mid")
    |> pick()
        | hit |> grab(v: 9): q
            |> readv(r: q): qv
            |> std/io:print.ln("q {{ qv:d }}")
        | miss |> std/io:print.ln("miss")
    |> readv(r): v
    |> std/io:print.ln("v {{ v:d }}")
    |> drop(r)
    |> std/io:print.ln("dropped")
| fail |> _