foo.pl

package Parent;

use Moo;

has 'parent' => ( 'is' => 'ro' );

sub core_attrs {
    my ($self) = @_;

    my $specs = 'Moo'->_constructor_maker_for('Parent')->all_attribute_specs;

    my @attr_names = keys %{$specs};

    return ( map { $_ => $self->$_ } @attr_names );
}

##############################################################################

package Foo;

use Moo;
extends 'Parent';

has 'foo' => ( 'is' => 'ro' );

##############################################################################

package Bar;

use Moo;
extends 'Parent';

has 'bar' => ( 'is' => 'ro' );

##############################################################################

package main;
use v5.32;

my $f = Foo->new( parent => 42, foo => 123 );
my $b = Bar->new( $f->core_attrs, bar => '456' );

use Data::Dumper;
say Dumper( $f, $b, { $f->core_attrs } );