Lazy load error_highlight, did_you_mean, and syntax_suggest

Defer requiring these gems from boot time to first
Exception#detailed_message call. They only enhance error display,
so loading them eagerly is unnecessary overhead.

On Apple M1 Pro, ruby -e1 boot time drops from 114ms to 30ms
(with user-installed gems), matching --disable-* flag performance.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: hsbt

gem_prelude.rb

@@ -8,20 +8,42 @@
   require 'bundled_gems'
 end if defined?(Gem)
 
-begin
-  require 'error_highlight'
-rescue LoadError
-  warn "`error_highlight' was not loaded."
-end if defined?(ErrorHighlight)
+if defined?(ErrorHighlight) || defined?(DidYouMean) || defined?(SyntaxSuggest)
+  module Ruby::DetailedError # :nodoc:
+    @loaded = false
 
-begin
-  require 'did_you_mean'
-rescue LoadError
-  warn "`did_you_mean' was not loaded."
-end if defined?(DidYouMean)
+    def self.loaded? = @loaded
 
-begin
-  require 'syntax_suggest/core_ext'
-rescue LoadError
-  warn "`syntax_suggest' was not loaded."
-end if defined?(SyntaxSuggest)
+    def self.load
+      return if @loaded
+      @loaded = true
+
+      begin
+        require 'error_highlight'
+      rescue LoadError
+        warn "`error_highlight' was not loaded."
+      end if defined?(ErrorHighlight)
+
+      begin
+        require 'did_you_mean'
+      rescue LoadError
+        warn "`did_you_mean' was not loaded."
+      end if defined?(DidYouMean)
+
+      begin
+        require 'syntax_suggest/core_ext'
+      rescue LoadError
+        warn "`syntax_suggest' was not loaded."
+      end if defined?(SyntaxSuggest)
+    end
+
+    def detailed_message(...)
+      return super if Ruby::DetailedError.loaded?
+      Ruby::DetailedError.load
+      # Re-dispatch to pick up the newly prepended methods from the gems
+      detailed_message(...)
+    end
+  end
+
+  Exception.prepend(Ruby::DetailedError)
+end