Address code review feedback for DatabaseChecker

- Refactor instance variables to result object pattern for thread safety
  - database_ready? now returns a Hash with :ready, :error_type, :error_message
  - print_database_failed now takes error_type and error_message as parameters
  - This makes the code thread-safe and improves maintainability

- Add RBS type signatures (required by project standards)
  - Created sig/react_on_rails/dev/database_checker.rbs
  - Added to Steepfile (alphabetically ordered)
  - Validated with bundle exec rake rbs:validate

- Add test case for DEBUG=false scenario
  - Verifies no warning is output when DEBUG is not enabled

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

Co-Authored-By: Claude <[email protected]>

Author: justin808

react_on_rails/Steepfile

@@ -28,6 +28,7 @@ target :lib do
   check "lib/react_on_rails.rb"
   check "lib/react_on_rails/configuration.rb"
   check "lib/react_on_rails/controller.rb"
+  check "lib/react_on_rails/dev/database_checker.rb"
   check "lib/react_on_rails/dev/file_manager.rb"
   check "lib/react_on_rails/dev/pack_generator.rb"
   check "lib/react_on_rails/dev/process_manager.rb"

react_on_rails/lib/react_on_rails/dev/database_checker.rb

@@ -30,38 +30,35 @@ def rails_available?
         def check_and_report_database
           print_check_header
 
-          if database_ready?
+          result = database_ready?
+          if result[:ready]
             print_database_ok
             true
           else
-            print_database_failed
+            print_database_failed(result[:error_type], result[:error_message])
             false
           end
         end
 
         def database_ready?
           # Try to establish connection and run a simple query
           ActiveRecord::Base.connection.execute("SELECT 1")
-          true
+          { ready: true }
         rescue ActiveRecord::NoDatabaseError
           # Database doesn't exist
-          @error_type = :no_database
-          false
+          { ready: false, error_type: :no_database }
         rescue ActiveRecord::PendingMigrationError
           # Database exists but migrations are pending
-          @error_type = :pending_migrations
-          false
+          { ready: false, error_type: :pending_migrations }
         rescue ActiveRecord::ConnectionNotEstablished,
                ActiveRecord::StatementInvalid => e
           # Connection failed or other database error
-          @error_type = :connection_error
-          @error_message = e.message
-          false
+          { ready: false, error_type: :connection_error, error_message: e.message }
         rescue StandardError => e
           # Unexpected error - log but don't block startup
           # This allows apps without databases to still use bin/dev
           warn "Database check warning: #{e.message}" if ENV["DEBUG"]
-          true
+          { ready: true }
         end
 
         def print_check_header
@@ -76,13 +73,13 @@ def print_database_ok
         end
 
         # rubocop:disable Metrics/AbcSize
-        def print_database_failed
+        def print_database_failed(error_type, error_message)
           puts "   #{Rainbow('✗').red} Database is not ready"
           puts ""
           puts Rainbow("❌ Database not set up!").red.bold
           puts ""
 
-          case @error_type
+          case error_type
           when :no_database
             puts Rainbow("The database does not exist.").yellow
             puts ""
@@ -96,9 +93,9 @@ def print_database_failed
             puts "   #{Rainbow('bin/rails db:migrate').green}   # Run pending migrations"
           when :connection_error
             puts Rainbow("Could not connect to the database.").yellow
-            if @error_message
+            if error_message
               puts ""
-              puts Rainbow("Error: #{@error_message}").red
+              puts Rainbow("Error: #{error_message}").red
             end
             puts ""
             puts Rainbow("Possible solutions:").cyan.bold

react_on_rails/sig/react_on_rails/dev/database_checker.rbs

@@ -0,0 +1,16 @@
+module ReactOnRails
+  module Dev
+    class DatabaseChecker
+      def self.check_database: () -> bool
+
+      private
+
+      def self.rails_available?: () -> bool
+      def self.check_and_report_database: () -> bool
+      def self.database_ready?: () -> Hash[Symbol, untyped]
+      def self.print_check_header: () -> void
+      def self.print_database_ok: () -> void
+      def self.print_database_failed: (Symbol?, String?) -> void
+    end
+  end
+end

react_on_rails/spec/react_on_rails/dev/database_checker_spec.rb

@@ -140,6 +140,11 @@ def self.connection; end
           allow(ENV).to receive(:[]).with("DEBUG").and_return("true")
           expect { described_class.check_database }.to output(/Database check warning/).to_stderr
         end
+
+        it "does not output a warning when DEBUG is not enabled" do
+          allow(ENV).to receive(:[]).with("DEBUG").and_return(nil)
+          expect { described_class.check_database }.not_to output(/Database check warning/).to_stderr
+        end
       end
     end
   end