fix(detection): handle partially-loaded Bundler in BundlerDefaults

RubyGems 4.0 defines the Bundler module without loading Bundler.settings,
causing NoMethodError when running as an installed gem. Explicitly require
bundler before accessing settings, with fallback to defaults on failure.

Author: svyatov

CHANGELOG.md

@@ -8,6 +8,10 @@ and [Conventional Commits](https://www.conventionalcommits.org/en/v1.0.0/).
 
 ## [Unreleased]
 
+### Fixed
+
+- Crash on Ruby 4.0 / RubyGems 4.0 where `Bundler.settings` was unavailable because Bundler was only partially loaded.
+
 ## [0.1.0] - 2026-02-10
 
 ### Added

lib/create_ruby_gem/detection/bundler_defaults.rb

@@ -66,9 +66,10 @@ def detect
 
       # @return [Bundler::Settings, nil]
       def default_settings
-        return nil unless defined?(::Bundler)
-
+        require 'bundler'
         ::Bundler.settings
+      rescue LoadError, StandardError
+        nil
       end
 
       # @param value [String, Object, nil]

spec/create_ruby_gem/detection/bundler_defaults_spec.rb

@@ -47,6 +47,13 @@ def settings.[](_key) = raise(StandardError, 'boom')
     expect(defaults).to eq(described_class::FALLBACKS)
   end
 
+  it 'returns fallbacks when Bundler.settings raises NoMethodError' do
+    stub_const('Bundler', Module.new)
+    defaults = described_class.new.detect
+
+    expect(defaults).to eq(described_class::FALLBACKS)
+  end
+
   it 'normalizes string booleans to actual booleans' do
     settings = { 'gem.coc' => 'true', 'gem.mit' => 'false' }
     defaults = described_class.new(settings: settings).detect