fix: Improve JsDependencyManager robustness and consistency

Address code review feedback to enhance error handling and consistency:

- Add exact: true flag to add_package method for consistency with add_npm_dependencies
- Add nil check for package_json in install_js_dependencies to prevent nil pointer errors
- Remove orphaned comment at end of module
- Update tests to verify exact: true flag is passed correctly
- Add test coverage for nil package_json scenario in install_js_dependencies

These changes improve code robustness while maintaining backward compatibility.

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

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

Author: justin808

lib/generators/react_on_rails/js_dependency_manager.rb

@@ -279,9 +279,9 @@ def add_package(package, dev: false)
           # Ensure package is in array format for package_json gem
           packages_array = [package]
           if dev
-            pj.manager.add(packages_array, type: :dev)
+            pj.manager.add(packages_array, type: :dev, exact: true)
           else
-            pj.manager.add(packages_array)
+            pj.manager.add(packages_array, exact: true)
           end
           true
         rescue StandardError => e
@@ -309,7 +309,13 @@ def install_js_dependencies
         # 1. react_on_rails gemspec requires shakapacker
         # 2. shakapacker gemspec requires package_json
         # 3. GeneratorHelper provides package_json method
-        package_json.manager.install
+        pj = package_json
+        unless pj
+          GeneratorMessages.add_warning("package_json not available, skipping dependency installation")
+          return false
+        end
+
+        pj.manager.install
         true
       rescue StandardError => e
         GeneratorMessages.add_warning(<<~MSG.strip)
@@ -323,8 +329,6 @@ def install_js_dependencies
         MSG
         false
       end
-
-      # No longer needed since package_json gem handles package manager detection
     end
   end
 end

spec/react_on_rails/generators/js_dependency_manager_spec.rb

@@ -142,13 +142,18 @@ def errors
     it "adds a single package successfully" do
       result = instance.send(:add_package, "react-on-rails@16.0.0")
       expect(result).to be(true)
-      expect(mock_manager).to have_received(:add).with(["react-on-rails@16.0.0"])
+      expect(mock_manager).to have_received(:add).with(["react-on-rails@16.0.0"], exact: true)
     end
 
     it "adds a dev dependency when dev: true" do
       result = instance.send(:add_package, "typescript", dev: true)
       expect(result).to be(true)
-      expect(mock_manager).to have_received(:add).with(["typescript"], type: :dev)
+      expect(mock_manager).to have_received(:add).with(["typescript"], type: :dev, exact: true)
+    end
+
+    it "uses exact: true flag for consistency with add_npm_dependencies" do
+      instance.send(:add_package, "some-package")
+      expect(mock_manager).to have_received(:add).with(["some-package"], exact: true)
     end
 
     it "returns false when package_json is nil" do
@@ -171,6 +176,16 @@ def errors
       expect(mock_manager).to have_received(:install)
     end
 
+    it "returns false and adds warning when package_json is nil" do
+      instance.package_json = nil
+
+      result = instance.send(:install_js_dependencies)
+
+      expect(result).to be(false)
+      expect(warnings.size).to be > 0
+      expect(warnings.first.to_s).to include("package_json not available")
+    end
+
     it "returns false and adds warning when install fails" do
       allow(mock_manager).to receive(:install).and_raise(StandardError, "Network timeout")
 
@@ -190,13 +205,13 @@ def errors
 
     it "adds react-on-rails with version for stable releases" do
       instance.send(:add_react_on_rails_package)
-      expect(mock_manager).to have_received(:add).with(["react-on-rails@16.0.0"])
+      expect(mock_manager).to have_received(:add).with(["react-on-rails@16.0.0"], exact: true)
     end
 
     it "adds react-on-rails without version for pre-releases" do
       stub_const("ReactOnRails::VERSION", "16.0.0-rc.1")
       instance.send(:add_react_on_rails_package)
-      expect(mock_manager).to have_received(:add).with(["react-on-rails"])
+      expect(mock_manager).to have_received(:add).with(["react-on-rails"], exact: true)
     end
 
     it "adds warning when add_package fails" do