docs: Enhance error handling documentation and test coverage

Address code review suggestions:

- Expand module documentation to explain graceful degradation philosophy
  in detail, including specific failure scenarios (network, permissions,
  package_json gem states)
- Add comprehensive tests for graceful degradation:
  * Verify setup_js_dependencies completes without raising when all
    package operations fail
  * Verify completion when install fails but add succeeds
  * Ensure warnings are generated but no errors that crash generators
- Improve add_package method documentation to clarify that exact: true
  flag ensures version pinning aligns with gem version, preventing
  mismatches between Ruby gem and NPM package

These changes improve code documentation and test coverage without
changing functionality. All 38 tests pass.

🤖 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

@@ -29,14 +29,20 @@ module Generators
     # installs what's actually needed from package.json. This prevents edge cases
     # where package.json was modified but dependencies weren't installed.
     #
-    # == Error Handling
-    # All dependency addition methods use a tolerant error handling approach:
-    # - Return false on failure instead of raising exceptions
-    # - Catch StandardError and add warnings to GeneratorMessages
-    # - Provide clear manual installation instructions in warnings
-    # This provides better UX - the generator completes successfully even if
-    # dependency installation fails (e.g., network issues), and users can
-    # manually install dependencies afterward.
+    # == Error Handling Philosophy
+    # All dependency addition methods use a graceful degradation approach:
+    # - Methods return false on failure instead of raising exceptions
+    # - StandardError is caught at the lowest level (add_package) and higher levels (add_*_dependencies)
+    # - Failures trigger user-facing warnings via GeneratorMessages
+    # - Warnings provide clear manual installation instructions
+    #
+    # This ensures the generator ALWAYS completes successfully, even when:
+    # - Network connectivity issues prevent package downloads
+    # - Package manager (npm/yarn/pnpm) has permission errors
+    # - package_json gem encounters unexpected states
+    #
+    # Users can manually run package installation commands after generator completion.
+    # This is preferable to generator crashes that leave Rails apps in incomplete states.
     #
     # == Usage
     # Include this module in generator classes and call setup_js_dependencies
@@ -256,6 +262,9 @@ def add_dev_dependencies
       # with version-specific handling (react-on-rails@VERSION).
       # For batch operations, use add_packages instead.
       #
+      # The exact: true flag ensures version pinning aligns with the gem version,
+      # preventing version mismatches between the Ruby gem and NPM package.
+      #
       # @param package [String] Package specifier (e.g., "react-on-rails@16.0.0")
       # @param dev [Boolean] Whether to add as dev dependency
       # @return [Boolean] true if successful, false otherwise

spec/react_on_rails/generators/js_dependency_manager_spec.rb

@@ -357,4 +357,31 @@ def errors
       expect(warning.to_s).to include("manually")
     end
   end
+
+  describe "graceful degradation" do
+    it "setup_js_dependencies completes successfully even when all package operations fail" do
+      # Simulate complete package installation failure
+      instance.add_npm_dependencies_result = false
+      instance.package_json = nil
+
+      # This should not raise any exceptions
+      expect { instance.send(:setup_js_dependencies) }.not_to raise_error
+
+      # Should have generated warnings for failures
+      expect(warnings.size).to be > 0
+      # But no errors that would crash the generator
+      expect(errors.size).to eq(0)
+    end
+
+    it "setup_js_dependencies completes when install fails but add succeeds" do
+      instance.add_npm_dependencies_result = true
+      allow(mock_manager).to receive(:install).and_raise(StandardError, "Network timeout")
+
+      # Should not raise despite install failure
+      expect { instance.send(:setup_js_dependencies) }.not_to raise_error
+
+      # Should have warning about install failure
+      expect(warnings.any? { |w| w.to_s.include?("installation failed") }).to be(true)
+    end
+  end
 end