diff --git a/Steepfile b/Steepfile
index bc0d583f43..0689f7f82d 100644
--- a/Steepfile
+++ b/Steepfile
@@ -28,6 +28,10 @@ target :lib do
   check "lib/react_on_rails.rb"
   check "lib/react_on_rails/configuration.rb"
   check "lib/react_on_rails/controller.rb"
+  check "lib/react_on_rails/dev/file_manager.rb"
+  check "lib/react_on_rails/dev/pack_generator.rb"
+  check "lib/react_on_rails/dev/process_manager.rb"
+  check "lib/react_on_rails/dev/server_manager.rb"
   check "lib/react_on_rails/git_utils.rb"
   check "lib/react_on_rails/helper.rb"
   check "lib/react_on_rails/packer_utils.rb"
diff --git a/lib/react_on_rails/dev/pack_generator.rb b/lib/react_on_rails/dev/pack_generator.rb
index a339d5860f..48e1f4eb4a 100644
--- a/lib/react_on_rails/dev/pack_generator.rb
+++ b/lib/react_on_rails/dev/pack_generator.rb
@@ -2,6 +2,7 @@
 
 require "English"
 require "stringio"
+require_relative "../packer_utils"
 
 module ReactOnRails
   module Dev
diff --git a/lib/react_on_rails/dev/server_manager.rb b/lib/react_on_rails/dev/server_manager.rb
index e1ff3e0825..63e8962634 100644
--- a/lib/react_on_rails/dev/server_manager.rb
+++ b/lib/react_on_rails/dev/server_manager.rb
@@ -3,6 +3,7 @@
 require "English"
 require "open3"
 require "rainbow"
+require_relative "../packer_utils"
 
 module ReactOnRails
   module Dev
diff --git a/sig/react_on_rails/dev/file_manager.rbs b/sig/react_on_rails/dev/file_manager.rbs
new file mode 100644
index 0000000000..88d3b4f93f
--- /dev/null
+++ b/sig/react_on_rails/dev/file_manager.rbs
@@ -0,0 +1,15 @@
+module ReactOnRails
+  module Dev
+    class FileManager
+      def self.cleanup_stale_files: () -> bool
+
+      private
+
+      def self.cleanup_overmind_sockets: () -> bool
+      def self.cleanup_rails_pid_file: () -> bool
+      def self.overmind_running?: () -> bool
+      def self.process_running?: (Integer) -> bool
+      def self.remove_file_if_exists: (String, String) -> bool
+    end
+  end
+end
diff --git a/sig/react_on_rails/dev/pack_generator.rbs b/sig/react_on_rails/dev/pack_generator.rbs
new file mode 100644
index 0000000000..76669b35e2
--- /dev/null
+++ b/sig/react_on_rails/dev/pack_generator.rbs
@@ -0,0 +1,19 @@
+module ReactOnRails
+  module Dev
+    class PackGenerator
+      def self.generate: (?verbose: bool) -> void
+
+      private
+
+      def self.run_pack_generation: (?silent: bool) -> bool
+      def self.should_run_directly?: () -> bool
+      def self.rails_available?: () -> bool
+      def self.run_rake_task_directly: (?silent: bool) -> bool
+      def self.load_rake_tasks: () -> void
+      def self.prepare_rake_task: () -> untyped
+      def self.capture_output: (bool) { () -> bool } -> bool
+      def self.handle_rake_error: (Exception, bool) -> void
+      def self.run_via_bundle_exec: (?silent: bool) -> (bool | nil)
+    end
+  end
+end
diff --git a/sig/react_on_rails/dev/process_manager.rbs b/sig/react_on_rails/dev/process_manager.rbs
new file mode 100644
index 0000000000..bdcd6dc464
--- /dev/null
+++ b/sig/react_on_rails/dev/process_manager.rbs
@@ -0,0 +1,22 @@
+module ReactOnRails
+  module Dev
+    class ProcessManager
+      VERSION_CHECK_TIMEOUT: Integer
+
+      def self.installed?: (String) -> bool
+      def self.ensure_procfile: (String) -> void
+      def self.run_with_process_manager: (String) -> void
+
+      private
+
+      def self.installed_in_current_context?: (String) -> bool
+      def self.version_flags_for: (String) -> Array[String]
+      def self.run_process_if_available: (String, Array[String]) -> bool
+      def self.run_process_outside_bundle: (String, Array[String]) -> bool
+      def self.process_available_in_system?: (String) -> bool
+      def self.with_unbundled_context: () { () -> untyped } -> untyped
+      def self.show_process_manager_installation_help: () -> void
+      def self.valid_procfile_path?: (String) -> bool
+    end
+  end
+end
diff --git a/sig/react_on_rails/dev/server_manager.rbs b/sig/react_on_rails/dev/server_manager.rbs
new file mode 100644
index 0000000000..a890627deb
--- /dev/null
+++ b/sig/react_on_rails/dev/server_manager.rbs
@@ -0,0 +1,39 @@
+module ReactOnRails
+  module Dev
+    class ServerManager
+      type mode = :development | :production_like | :static | :hmr
+
+      def self.start: (mode, String?, ?verbose: bool, ?route: String?, ?rails_env: String?) -> void
+      def self.kill_processes: () -> void
+      def self.development_processes: () -> Hash[String, String]
+      def self.kill_running_processes: () -> bool
+      def self.find_process_pids: (String) -> Array[Integer]
+      def self.terminate_processes: (Array[Integer]) -> void
+      def self.kill_port_processes: (Array[Integer]) -> bool
+      def self.find_port_pids: (Integer) -> Array[Integer]
+      def self.cleanup_socket_files: () -> bool
+      def self.print_kill_summary: (bool) -> void
+      def self.show_help: () -> void
+      def self.run_from_command_line: (?Array[String]) -> void
+
+      private
+
+      def self.help_usage: () -> String
+      def self.help_commands: () -> String
+      def self.help_options: () -> String
+      def self.help_customization: () -> String
+      def self.help_mode_details: () -> String
+      def self.help_troubleshooting: () -> String
+      def self.run_production_like: (?_verbose: bool, ?route: String?, ?rails_env: String?) -> void
+      def self.run_static_development: (String, ?verbose: bool, ?route: String?) -> void
+      def self.run_development: (String, ?verbose: bool, ?route: String?) -> void
+      def self.print_server_info: (String, Array[String], ?Integer, ?route: String?) -> void
+      def self.print_procfile_info: (String, ?route: String?) -> void
+      def self.procfile_port: (String) -> Integer
+      def self.box_border: (Integer) -> String
+      def self.box_bottom: (Integer) -> String
+      def self.box_empty_line: (Integer) -> String
+      def self.format_box_line: (String, Integer) -> String
+    end
+  end
+end
diff --git a/spec/react_on_rails/binstubs/dev_spec.rb b/spec/react_on_rails/binstubs/dev_spec.rb
index 0f699af27d..c2ff504a2e 100644
--- a/spec/react_on_rails/binstubs/dev_spec.rb
+++ b/spec/react_on_rails/binstubs/dev_spec.rb
@@ -4,6 +4,7 @@
 
 RSpec.describe "bin/dev script" do
   let(:script_path) { "lib/generators/react_on_rails/templates/base/base/bin/dev" }
+  let(:dummy_dev_path) { "spec/dummy/bin/dev" }
 
   # To suppress stdout during tests
   original_stderr = $stderr
@@ -58,4 +59,28 @@ def setup_script_execution_for_tool_tests
 
     load script_path
   end
+
+  # Integration test: verify bin/dev can load without NameError
+  describe "integration test" do
+    it "spec/dummy/bin/dev can load the template script without errors" do
+      # This test verifies that all required dependencies are properly loaded
+      # when bin/dev is executed, catching issues like missing require statements
+      expect(File.exist?(dummy_dev_path)).to be true
+      expect(File.exist?(script_path)).to be true
+
+      # Verify the dummy script references the template
+      dummy_content = File.read(dummy_dev_path)
+      expect(dummy_content).to include(script_path)
+    end
+
+    it "can require react_on_rails/dev and access all necessary modules" do
+      # This catches missing require statements in pack_generator.rb and other files
+      # If PackerUtils isn't required, this would fail with NameError
+      require "react_on_rails/dev"
+
+      expect { ReactOnRails::Dev::ServerManager }.not_to raise_error
+      expect { ReactOnRails::Dev::PackGenerator }.not_to raise_error
+      expect { ReactOnRails::PackerUtils }.not_to raise_error
+    end
+  end
 end
diff --git a/spec/react_on_rails/dev/pack_generator_spec.rb b/spec/react_on_rails/dev/pack_generator_spec.rb
index 19afb35df7..751725eccb 100644
--- a/spec/react_on_rails/dev/pack_generator_spec.rb
+++ b/spec/react_on_rails/dev/pack_generator_spec.rb
@@ -4,6 +4,15 @@
 require "react_on_rails/dev/pack_generator"
 
 RSpec.describe ReactOnRails::Dev::PackGenerator do
+  # Integration test: verify PackerUtils is properly required
+  describe "module dependencies" do
+    it "can access ReactOnRails::PackerUtils without errors" do
+      # This test ensures the require statement is present in pack_generator.rb
+      # If the require is missing, this will raise NameError: uninitialized constant
+      expect { ReactOnRails::PackerUtils }.not_to raise_error
+    end
+  end
+
   describe ".generate" do
     context "when shakapacker precompile hook is configured" do
       before do
diff --git a/spec/react_on_rails/generators/generator_helper_spec.rb b/spec/react_on_rails/generators/generator_helper_spec.rb
index f00c9e4a24..eb8b447549 100644
--- a/spec/react_on_rails/generators/generator_helper_spec.rb
+++ b/spec/react_on_rails/generators/generator_helper_spec.rb
@@ -13,6 +13,9 @@
       let(:mock_manager) { instance_double("PackageJson::Manager") } # rubocop:disable RSpec/VerifiedDoubleReference
 
       before do
+        # Stub PackageJson constant so instance_double can reference it
+        stub_const("PackageJson", Class.new) unless defined?(PackageJson)
+
         allow(self).to receive(:package_json).and_return(mock_package_json)
         allow(mock_package_json).to receive(:manager).and_return(mock_manager)
       end