Ah, unfortunately what I forgot to put in the original post is what rethrow_exception does...

sub rethrow_exception
{
    my $exception = shift;

    # debug that the exception is being rethrow, so we can trace it in
+ debugs
    debug( 'Exception ' . ( ref($exception) || 'GENERIC Perl Died: ' .
+ $exception ) . ' being rethrown', 'true' );

    my @trace = caller_string();

    # Check if its a string...
    if ( !ref $exception )
    {
        Zymonic::Exception::from_die->throw(
            error       => 'GENERIC Perl Died: ' . $exception,
            email       => 'sysadmin',
            zymocallers => \@trace
        );
    }
    elsif ( ref($exception) !~ /Zymonic::Exception/ )
    {
        Zymonic::Exception::from_die->throw(
            error       => Dumper($exception),
            email       => 'sysadmin',
            zymocallers => \@trace
        );
    }
    else
    {

        # We have an exception - just rethrow it, adding additional tr
+ace to it
        $exception->{zymocallers} =
          [ ( ref( $exception->{zymocallers} ) ? @{ $exception->{zymoc
+allers} } : () ), @trace ];
        $exception->rethrow();
    }
}
[download]

So effectively we're already doing what Carp can do in terms of stack tracing on the error.

The other issue with even trying to use Carp is that as far as I can tell Perl doesn't seem to have thrown an error before the attempt to reload fails - and yet the documentation suggests that there should have been an error previously. Since I don't have any evidence of that previous error I'm at a loss to know how to trap it and make Carp (or our own exception handling) give us more information about it...

But thank you - reading the Carp documentation has given me some other internal perl vars to check.