detach.pl

use Mojolicious::Lite;

# Catch magical detach exception and rethrow everything else
hook around_dispatch => sub {
  my ($next, $c) = @_;
  return if eval { $next->(); 1 };
  die $@ unless $@ eq "MOJO_DETACH\n";
};

# Throw magical detach exception
helper detach => sub { die "MOJO_DETACH\n" };

helper some_helper => sub {
  my $self = shift;
  $self->render(text => 'I take over!');
  $self->detach;
};

get '/' => sub {
  my $self = shift;
  $self->some_helper;
  $self->render(text => 'I will never be reached!');
};

app->start;

This does not work for non-blocking operations and there is no solution for that.