html-map.php

<?php

add_action( 'init', function() {
  $html_map = [
    'howdy/world' => 'howdy',
  ];
    
  $current_path = parse_url( $_SERVER['REQUEST_URI'], PHP_URL_PATH );
  if ( in_array( $current_path, array_keys( $html_map ), true ) ) {
    $filename = $html_map[ $current_path ];
    $contents = file_get_contents( __DIR__ . '/docs/' . $filename . '.html';
    echo $contents;
    exit;
  }
} );