the second method is called via the modifier "after" which guarantees do_n() already happened.

Where do you see do_n assigning anything to "n"? As I explained, "after do_n already happened" is too soon. The "trigger" is "as soon as it returns".

$self->{n} = sub {
   my ($self) = @_;
   my $rv = $self->do_n();
   $self->do_n2();            # Too soon
   return $rv;
}->($self);
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