Address PR #1907 code review feedback

Fix two critical issues identified in code review:

1. Add missing StringIO require to prevent runtime errors in Ruby 3.0+
   - StringIO is not auto-loaded in Ruby 3.0+ and was being used in
     capture_output method without being explicitly required
   - This could cause NameError when running in silent mode

2. Update test suite to handle both execution paths
   - Previous tests only stubbed system calls but didn't account for
     the new Bundler context detection logic
   - Split tests into two contexts: Bundler context (direct Rake) and
     non-Bundler context (bundle exec)
   - Each context now properly stubs the appropriate execution method

All tests pass and RuboCop shows no violations.

Related to: #1907

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

Author: justin808

lib/react_on_rails/dev/pack_generator.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 
 require "English"
+require "stringio"
 
 module ReactOnRails
   module Dev

spec/react_on_rails/dev/pack_generator_spec.rb

@@ -5,27 +5,65 @@
 
 RSpec.describe ReactOnRails::Dev::PackGenerator do
   describe ".generate" do
-    it "runs pack generation successfully in verbose mode" do
-      command = "bundle exec rake react_on_rails:generate_packs"
-      allow(described_class).to receive(:system).with(command).and_return(true)
+    context "when in Bundler context with Rails available" do
+      before do
+        stub_const("Bundler", Module.new)
+        allow(ENV).to receive(:[]).and_call_original
+        allow(ENV).to receive(:[]).with("BUNDLE_GEMFILE").and_return("/path/to/Gemfile")
+        allow(described_class).to receive(:rails_available?).and_return(true)
+      end
 
-      expect { described_class.generate(verbose: true) }
-        .to output(/📦 Generating React on Rails packs.../).to_stdout_from_any_process
-    end
+      it "runs pack generation successfully in verbose mode using direct rake execution" do
+        allow(described_class).to receive(:run_rake_task_directly).and_return(true)
+
+        expect { described_class.generate(verbose: true) }
+          .to output(/📦 Generating React on Rails packs.../).to_stdout_from_any_process
+        expect(described_class).to have_received(:run_rake_task_directly)
+      end
+
+      it "runs pack generation successfully in quiet mode using direct rake execution" do
+        allow(described_class).to receive(:run_rake_task_directly).and_return(true)
 
-    it "runs pack generation successfully in quiet mode" do
-      command = "bundle exec rake react_on_rails:generate_packs > /dev/null 2>&1"
-      allow(described_class).to receive(:system).with(command).and_return(true)
+        expect { described_class.generate(verbose: false) }
+          .to output(/📦 Generating packs\.\.\. ✅/).to_stdout_from_any_process
+        expect(described_class).to have_received(:run_rake_task_directly)
+      end
 
-      expect { described_class.generate(verbose: false) }
-        .to output(/📦 Generating packs\.\.\. ✅/).to_stdout_from_any_process
+      it "exits with error when pack generation fails" do
+        allow(described_class).to receive(:run_rake_task_directly).and_return(false)
+
+        expect { described_class.generate(verbose: false) }.to raise_error(SystemExit)
+      end
     end
 
-    it "exits with error when pack generation fails" do
-      command = "bundle exec rake react_on_rails:generate_packs > /dev/null 2>&1"
-      allow(described_class).to receive(:system).with(command).and_return(false)
+    context "when not in Bundler context" do
+      before do
+        stub_const("Bundler", nil) unless defined?(Bundler)
+        allow(described_class).to receive(:should_run_directly?).and_return(false)
+      end
+
+      it "runs pack generation successfully in verbose mode using bundle exec" do
+        command = "bundle exec rake react_on_rails:generate_packs"
+        allow(described_class).to receive(:system).with(command).and_return(true)
+
+        expect { described_class.generate(verbose: true) }
+          .to output(/📦 Generating React on Rails packs.../).to_stdout_from_any_process
+      end
+
+      it "runs pack generation successfully in quiet mode using bundle exec" do
+        command = "bundle exec rake react_on_rails:generate_packs > /dev/null 2>&1"
+        allow(described_class).to receive(:system).with(command).and_return(true)
+
+        expect { described_class.generate(verbose: false) }
+          .to output(/📦 Generating packs\.\.\. ✅/).to_stdout_from_any_process
+      end
+
+      it "exits with error when pack generation fails" do
+        command = "bundle exec rake react_on_rails:generate_packs > /dev/null 2>&1"
+        allow(described_class).to receive(:system).with(command).and_return(false)
 
-      expect { described_class.generate(verbose: false) }.to raise_error(SystemExit)
+        expect { described_class.generate(verbose: false) }.to raise_error(SystemExit)
+      end
     end
   end
 end