Treat missing marshal files as empty record sets

MarshalLoader#read_raw raised Errno::ENOENT when the dump file did not
exist, which prevented bootstrapping a dataset before any dump was
produced. Align the behavior with QueryLoader's empty-table fallback so
loading a missing table yields an empty record set instead.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: AZQ1994

lib/simple_master/loader/marshal_loader.rb

@@ -4,10 +4,15 @@ module SimpleMaster
   class Loader
     class MarshalLoader < Loader
       def read_raw(table)
-        File.read("#{@options[:path]}/#{table.klass.table_name}.marshal")
+        path = "#{@options[:path]}/#{table.klass.table_name}.marshal"
+        return nil unless File.exist?(path)
+
+        File.read(path)
       end
 
       def build_records(_klass, raw)
+        return [] if raw.nil?
+
         Marshal.load(raw) # rubocop:disable Security/MarshalLoad
       end
     end

spec/simple_master/loader/marshal_loader_spec.rb

@@ -23,4 +23,19 @@
       end
     end
   end
+
+  it "treats missing marshal files as empty record sets instead of raising" do
+    Dir.mktmpdir do |dir|
+      loader = described_class.new(path: dir)
+      dataset = SimpleMaster::Storage::Dataset.new(loader: loader)
+
+      expect { dataset.load }.not_to raise_error
+
+      SimpleMaster.use_dataset(dataset) do
+        expect(Weapon.all).to eq([])
+        expect(Level.all).to eq([])
+        expect(Enemy.all).to eq([])
+      end
+    end
+  end
 end