Thanks for the feedback.

As well as the solutions mentioned, I've just realized it's probably as easy as defining import in Foo::Bar::Error to be something like:

{
  my %SEEN;
  our @CARP_NOT;

  sub import
  {
    my $caller = caller;

    return if $SEEN{$caller};

    __PACKAGE__->export_to_level(1, @_);

    push @CARP_NOT, $caller;
  }
}
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That seems to work (passes all my tests anyway!) - if not, I've now got some useful alternatives.

Again, thanks for the advice.