Revert Pro app to async and fix ReScript build in precompile hook

- Revert Pro dummy app back to async: true (Pro supports Selective Hydration)
- Fix ReScript build to run from Rails root instead of current directory
- Use File.join for proper path resolution of config files
- Wrap build commands in Dir.chdir(rails_root) for correct execution
- Add early Rails root resolution with proper error handling
- Remove unnecessary defer strategy comment from initializer
- Add blank line before main execution section for style

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

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

Author: justin808

react_on_rails_pro/spec/dummy/app/views/layouts/application.html.erb

@@ -24,12 +24,13 @@
                           media: 'all',
                           'data-turbo-track': 'reload') %>
 
-  <%# Use defer: true to ensure proper script execution order.
-      When using generated component packs (auto_load_bundle), defer ensures
-      component registrations complete before React hydration begins.
+  <%# async: true is the recommended approach for Shakapacker >= 8.2.0 (currently using 9.3.0).
+      It enables React 18's Selective Hydration and provides optimal Time to Interactive (TTI).
+      Use immediate_hydration feature to control hydration timing for Selective/Immediate Hydration.
+      See docs/building-features/streaming-server-rendering.md
       skip_js_packs param is used for testing purposes to simulate hydration failure %>
   <% unless params[:skip_js_packs] == 'true' %>
-    <%= javascript_pack_tag('client-bundle', 'data-turbo-track': 'reload', defer: true) %>
+    <%= javascript_pack_tag('client-bundle', 'data-turbo-track': 'reload', async: true) %>
   <% end %>
   <%= csrf_meta_tags %>
 </head>

react_on_rails_pro/spec/dummy/bin/shakapacker-precompile-hook

@@ -22,23 +22,35 @@ end
 
 # Build ReScript if needed
 def build_rescript_if_needed
+  # Find Rails root directory
+  rails_root = find_rails_root
+  unless rails_root
+    warn "⚠️  Warning: Could not find Rails root. Skipping ReScript build."
+    return
+  end
+
   # Check for both old (bsconfig.json) and new (rescript.json) config files
-  return unless File.exist?("bsconfig.json") || File.exist?("rescript.json")
+  bsconfig_path = File.join(rails_root, "bsconfig.json")
+  rescript_config_path = File.join(rails_root, "rescript.json")
+  return unless File.exist?(bsconfig_path) || File.exist?(rescript_config_path)
 
   puts "🔧 Building ReScript..."
 
   # Cross-platform package manager detection
   yarn_available = system("yarn", "--version", out: File::NULL, err: File::NULL)
   npm_available = system("npm", "--version", out: File::NULL, err: File::NULL)
 
-  success = if yarn_available
-              system("yarn", "build:rescript")
-            elsif npm_available
-              system("npm", "run", "build:rescript")
-            else
-              warn "⚠️  Warning: Neither yarn nor npm found. Skipping ReScript build."
-              return
-            end
+  # Run build command from Rails root directory
+  success = Dir.chdir(rails_root) do
+    if yarn_available
+      system("yarn", "build:rescript")
+    elsif npm_available
+      system("npm", "run", "build:rescript")
+    else
+      warn "⚠️  Warning: Neither yarn nor npm found. Skipping ReScript build."
+      return false
+    end
+  end
 
   if success
     puts "✅ ReScript build completed successfully"
@@ -85,6 +97,7 @@ def generate_packs_if_needed
     exit 1
   end
 end
+
 # Main execution
 begin
   build_rescript_if_needed

react_on_rails_pro/spec/dummy/config/initializers/react_on_rails.rb

@@ -36,9 +36,6 @@ def self.adjust_props_for_client_side_hydration(_component_name, props)
   config.components_subdirectory = "ror-auto-load-components"
   config.auto_load_bundle = true
 
-  # Don't explicitly set generated_component_packs_loading_strategy - let it default to :defer
-  # which ensures generated component packs load and register components before main bundle executes
-
   ################################################################################
   # Pro Feature Testing: Server Bundle Security
   ################################################################################