What is the right way to recognize a bad executable when creating a Proc::Async?

And why, when I try to send the bad executable input does my CATCH not seem to catch the error?

try {
    my $proc = Proc::Async.new('bad-executable', :w);

    my $done = $proc.start;

    say "try sending to bad executable";

    await $proc.say("hi there");

    say "worked";

    $proc.close-stdin;

    await $done;

    CATCH {
        default {
            say "caught";
        }
    }
}

say "done";
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Running:

$ perl6 -v
This is Rakudo version 2017.01 built on MoarVM version 2017.01
implementing Perl 6.c.
$ perl6 testit.pl
try sending to bad executable
$
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