Fix RSpec helper optimization gap with private SSR directories (#1838)

## Summary

Fixes an optimization gap in the RSpec helper where server bundle
staleness was not detected when using private SSR directories
(introduced in PR #1798).

- **Issue**: Default `webpack_generated_files: ['manifest.json']`
configuration only monitored client assets, missing server bundle
changes in private `ssr-generated/` directory
- **Impact**: Tests could run with stale server-side code, leading to
incorrect test results
- **Solution**: Enhanced `ensure_webpack_generated_files_exists` to
automatically include server bundles and other critical files in
monitoring list

## Root Cause

PR #1798 moved server bundles to private directories for security, but
the RSpec helper optimization continued monitoring only `manifest.json`
by default. This created a gap where:

1. Server bundle changes in `ssr-generated/server-bundle.js` 
2. Client assets remain fresh in `public/packs-test/manifest.json`
3. RSpec helper reports "no rebuild needed" ❌
4. Tests run with stale server-side code

**Why this worked before:** Prior to PR #1798, both client and server
bundles were co-located in the same `public/packs/` directory, so the
RSpec helper's fallback logic would detect server bundle staleness even
when only monitoring `manifest.json`.

## Fix Details

**Before:**
```ruby
def ensure_webpack_generated_files_exists
  return unless webpack_generated_files.empty?  # ❌ Never runs with default config
  # ...
end
```

**After:**
```ruby
def ensure_webpack_generated_files_exists
  all_required_files = [
    "manifest.json",
    server_bundle_js_file,
    rsc_bundle_js_file,
    react_client_manifest_file,
    react_server_client_manifest_file
  ].compact_blank

  if webpack_generated_files.empty?
    self.webpack_generated_files = all_required_files
  else
    missing_files = all_required_files.reject { |file| webpack_generated_files.include?(file) }
    self.webpack_generated_files += missing_files if missing_files.any?
  end
end
```

## Testing

- ✅ Comprehensive test coverage added for all scenarios
- ✅ Verified fix resolves gap with test apps
- ✅ Backward compatibility maintained
- ✅ Works across different directory configurations

## Test plan

- [x] RSpec helper correctly detects server bundle staleness with
default config
- [x] Cross-directory monitoring works (client in `public/`, server in
`ssr-generated/`)
- [x] Existing configurations continue working unchanged
- [x] Edge cases handled (nil values, custom configurations)

Fixes #1822

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

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<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- Bug Fixes
- More reliable two-phase population of required Webpack assets,
avoiding duplicates.
- Preserves pre-existing custom files while adding only missing
essentials.
- Avoids adding nil/empty entries when server bundle or manifests are
absent.
  - Includes RSC and additional Pro manifests when configured.
  - Improves server-bundle monitoring behavior for faster test runs.

- Tests
- Added comprehensive tests covering asset inclusion, duplication
prevention, custom configs, RSC support, and multi-directory monitoring.

<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Co-authored-by: Justin Gordon <[email protected]>
Co-authored-by: Claude <[email protected]>

Author: 3 people

lib/react_on_rails/configuration.rb

@@ -429,18 +429,23 @@ def configure_generated_assets_dirs_deprecation
     end
 
     def ensure_webpack_generated_files_exists
-      return unless webpack_generated_files.empty?
-
-      files = ["manifest.json", server_bundle_js_file]
+      all_required_files = ["manifest.json", server_bundle_js_file]
 
       if ReactOnRails::Utils.react_on_rails_pro?
         pro_config = ReactOnRailsPro.configuration
-        files << pro_config.rsc_bundle_js_file
-        files << pro_config.react_client_manifest_file
-        files << pro_config.react_server_client_manifest_file
+        all_required_files << pro_config.rsc_bundle_js_file
+        all_required_files << pro_config.react_client_manifest_file
+        all_required_files << pro_config.react_server_client_manifest_file
       end
 
-      self.webpack_generated_files = files.compact_blank
+      all_required_files = all_required_files.compact_blank
+
+      if webpack_generated_files.empty?
+        self.webpack_generated_files = all_required_files
+      else
+        missing_files = all_required_files.reject { |file| webpack_generated_files.include?(file) }
+        self.webpack_generated_files += missing_files if missing_files.any?
+      end
     end
 
     def configure_skip_display_none_deprecation

spec/react_on_rails/configuration_spec.rb

@@ -287,6 +287,17 @@ module ReactOnRails
         context "with Pro license" do
           before do
             allow(ReactOnRails::Utils).to receive(:react_on_rails_pro?).and_return(true)
+
+            # Mock Pro configuration to avoid dependency on Pro being installed
+            pro_module = Module.new
+            pro_config = double("ProConfiguration") # rubocop:disable RSpec/VerifiedDoubles
+            allow(pro_config).to receive_messages(
+              rsc_bundle_js_file: "",
+              react_client_manifest_file: "react-client-manifest.json",
+              react_server_client_manifest_file: "react-server-client-manifest.json"
+            )
+            pro_module.define_singleton_method(:configuration) { pro_config }
+            stub_const("ReactOnRailsPro", pro_module)
           end
 
           it "defaults to :async" do
@@ -626,6 +637,117 @@ module ReactOnRails
         end
       end
     end
+
+    describe "#ensure_webpack_generated_files_exists" do
+      let(:config) { described_class.new }
+
+      before do
+        # Reset to test defaults
+        config.server_bundle_js_file = "server-bundle.js"
+        allow(ReactOnRails::Utils).to receive(:react_on_rails_pro?).and_return(false)
+      end
+
+      context "when webpack_generated_files has default manifest.json only" do
+        it "automatically includes server bundle when configured" do
+          config.webpack_generated_files = %w[manifest.json]
+
+          config.send(:ensure_webpack_generated_files_exists)
+
+          expect(config.webpack_generated_files).to eq(%w[manifest.json server-bundle.js])
+        end
+
+        it "does not duplicate manifest.json" do
+          config.webpack_generated_files = %w[manifest.json]
+
+          config.send(:ensure_webpack_generated_files_exists)
+
+          expect(config.webpack_generated_files.count("manifest.json")).to eq(1)
+        end
+      end
+
+      context "when webpack_generated_files is empty" do
+        it "populates with all required files" do
+          config.webpack_generated_files = []
+
+          config.send(:ensure_webpack_generated_files_exists)
+
+          expect(config.webpack_generated_files).to eq(%w[manifest.json server-bundle.js])
+        end
+      end
+
+      context "when server bundle already included" do
+        it "does not duplicate entries" do
+          config.webpack_generated_files = %w[manifest.json server-bundle.js]
+
+          config.send(:ensure_webpack_generated_files_exists)
+
+          expect(config.webpack_generated_files).to eq(%w[manifest.json server-bundle.js])
+          expect(config.webpack_generated_files.count("server-bundle.js")).to eq(1)
+        end
+      end
+
+      context "when custom files are configured" do
+        it "preserves custom files and adds missing critical files" do
+          config.webpack_generated_files = %w[manifest.json custom-bundle.js]
+
+          config.send(:ensure_webpack_generated_files_exists)
+
+          expect(config.webpack_generated_files).to include("manifest.json")
+          expect(config.webpack_generated_files).to include("custom-bundle.js")
+          expect(config.webpack_generated_files).to include("server-bundle.js")
+        end
+      end
+
+      context "when server bundle is not configured" do
+        it "does not add empty server bundle" do
+          config.server_bundle_js_file = ""
+          config.webpack_generated_files = %w[manifest.json]
+
+          config.send(:ensure_webpack_generated_files_exists)
+
+          expect(config.webpack_generated_files).not_to include("")
+          expect(config.webpack_generated_files).to eq(%w[manifest.json])
+        end
+
+        it "does not add nil server bundle" do
+          config.server_bundle_js_file = nil
+          config.webpack_generated_files = %w[manifest.json]
+
+          config.send(:ensure_webpack_generated_files_exists)
+
+          expect(config.webpack_generated_files).not_to include(nil)
+          expect(config.webpack_generated_files).to eq(%w[manifest.json])
+        end
+      end
+
+      context "when ensuring server bundle monitoring for RSpec optimization" do
+        it "ensures server bundle in private directory is monitored with default config" do
+          # Simulate default generator configuration
+          config.webpack_generated_files = %w[manifest.json]
+          config.server_bundle_js_file = "server-bundle.js"
+          config.server_bundle_output_path = "ssr-generated"
+
+          config.send(:ensure_webpack_generated_files_exists)
+
+          # Critical: server bundle must be included for RSpec helper optimization to work
+          expect(config.webpack_generated_files).to include("server-bundle.js")
+        end
+
+        it "handles all files being in different directories" do
+          # Simulate cross-directory scenario
+          config.webpack_generated_files = %w[manifest.json]
+          config.server_bundle_js_file = "server-bundle.js"
+          config.server_bundle_output_path = "ssr-generated"
+          config.generated_assets_dir = "public/packs"
+
+          config.send(:ensure_webpack_generated_files_exists)
+
+          # All critical files should be monitored regardless of directory
+          expect(config.webpack_generated_files).to include("manifest.json")
+          expect(config.webpack_generated_files).to include("server-bundle.js")
+        end
+      end
+    end
   end
 end