Instead, we can create an "empty" subtype for the coercion:
- subtype 'My.HTTP.Headers' => as class_type('HTTP::Headers');
+ subtype 'My.HTTP::Headers' => as class_type('HTTP::Headers');
- coerce 'My.HTTP.Headers'
+ coerce 'My.HTTP::Headers'
=> from 'HashRef'
=> via { HTTP::Headers->new( %{$_} ) };