Fix component registration race condition by using defer for all scripts

Changes the default loading strategy from :async to :defer to prevent
race conditions where React hydration starts before component registrations
complete.

Root cause: With async script loading, both client-bundle and generated
component packs can execute in any order. When client-bundle executes first,
React attempts to hydrate components that haven't been registered yet,
causing "Could not find component registered with name X" errors.

Solution:
- Default generated_component_packs_loading_strategy to :defer (was :async)
- Use defer: true for client-bundle in dummy app layout
- Update comments to reflect new strategy

With defer, scripts execute in DOM order after parsing, ensuring:
1. Generated component packs load first
2. Components register before main bundle executes
3. React hydration finds all registered components

Fixes CI failures in:
- spec/system/integration_spec.rb[1:1:6:1:2]
- spec/system/integration_spec.rb[1:1:6:2:2]

Author: justin808

lib/react_on_rails/configuration.rb

@@ -154,9 +154,9 @@ def check_component_registry_timeout
       raise ReactOnRails::Error, "component_registry_timeout must be a positive integer"
     end
 
-    # rubocop:disable Metrics/CyclomaticComplexity, Metrics/PerceivedComplexity
+    # rubocop:disable Metrics/CyclomaticComplexity
     def validate_generated_component_packs_loading_strategy
-      # rubocop:enable Metrics/CyclomaticComplexity, Metrics/PerceivedComplexity
+      # rubocop:enable Metrics/CyclomaticComplexity
 
       if defer_generated_component_packs
         if %i[async sync].include?(generated_component_packs_loading_strategy)
@@ -176,12 +176,11 @@ def validate_generated_component_packs_loading_strategy
         1. Use :sync or :defer loading strategy instead of :async
         2. Upgrade to Shakapacker v8.2.0 or above to enable async script loading
       MSG
-      if PackerUtils.supports_async_loading?
-        self.generated_component_packs_loading_strategy ||= :async
-      elsif generated_component_packs_loading_strategy.nil?
-        Rails.logger.warn("**WARNING** #{msg}")
-        self.generated_component_packs_loading_strategy = :sync
-      elsif generated_component_packs_loading_strategy == :async
+      if generated_component_packs_loading_strategy.nil?
+        # Use defer as the default to ensure generated component packs load and register
+        # components before main bundle executes, avoiding race conditions with async loading
+        self.generated_component_packs_loading_strategy = :defer
+      elsif generated_component_packs_loading_strategy == :async && !PackerUtils.supports_async_loading?
         raise ReactOnRails::Error, "**ERROR** #{msg}"
       end
 

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

@@ -9,16 +9,10 @@
 
   <%= yield :head %>
 
-  <%# Conditionally use defer: true for pages with Redux shared stores (inline registration).
-      Modern apps should use async: true for optimal performance. See docs for details:
-      docs/building-features/streaming-server-rendering.md %>
-  <% if uses_redux_shared_store? %>
-    <%# defer: true required for Redux shared stores with inline component registration %>
-    <%= javascript_pack_tag('client-bundle', 'data-turbo-track': 'reload', defer: true) %>
-  <% else %>
-    <%# async: true is the recommended approach for modern apps (Shakapacker >= 8.2.0) %>
-    <%= javascript_pack_tag('client-bundle', 'data-turbo-track': 'reload', async: true) %>
-  <% end %>
+  <%# 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. %>
+  <%= javascript_pack_tag('client-bundle', 'data-turbo-track': 'reload', defer: true) %>
 
   <%= csrf_meta_tags %>
 </head>

spec/dummy/config/initializers/react_on_rails.rb

@@ -42,5 +42,6 @@ def self.adjust_props_for_client_side_hydration(component_name, props)
   config.components_subdirectory = "startup"
   config.auto_load_bundle = true
   config.immediate_hydration = false
-  config.generated_component_packs_loading_strategy = :defer
+  # 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
 end