039 transition metatype

// PIN: a Transition-metatype tap handler that stringifies its fields.
// taps.eventToString/branchToString ARE emitted into the output's taps
// namespace (src/emitter_helpers.zig), but flow syntax cannot reach them:
// call-in-argument is KORU104-refused, and passing the enum fields bare
// (`t.source`) emits zig that does not compile (EventEnum into []const u8).
const std = @import("std");
~import std/taps
~tor hello {}
~tor goodbye {}
~[comptime|runtime] tor logger { source: string, branch: string, destination: ?string }
~proc hello|zig {
    std.debug.print("Hello executed\n", .{});
}
~proc goodbye|zig {
    std.debug.print("Goodbye executed\n", .{});
}
~[comptime|runtime] proc logger|zig {
    if (destination) |dest| {
        std.debug.print("Transition: {s}.{s} -> {s}\n", .{source, branch, dest});
    } else {
        std.debug.print("Transition: {s}.{s} -> terminal\n", .{source, branch});
    }
}
~tap(* -> *)
| Transition t |> logger(source: taps.eventToString(t.source), branch: taps.branchToString(t.branch), destination: if (t.destination) |d| taps.eventToString(d) else null)

~hello() |> goodbye()