[codex] Reduce packaged gem files

shakapacker.gemspec

@@ -28,10 +28,6 @@ Gem::Specification.new do |s|
   s.add_development_dependency "rubocop"
   s.add_development_dependency "rubocop-performance"
 
-  s.files = `git ls-files -z`.split("\x0").reject { |f|
-    f.match(%r{^(test|spec|features|tmp|node_modules|packages|coverage|Gemfile.lock|rakelib)($|/)}) ||
-      f.end_with?(".gem")
-  } + Dir.glob("sig/**/*.rbs")
-
-  s.test_files = `git ls-files -- test/*`.split("\n")
+  s.files = `git ls-files -z CHANGELOG.md MIT-LICENSE README.md shakapacker.gemspec lib sig`.split("\x0")
+  s.test_files = []
 end

spec/shakapacker/gemspec_spec.rb

@@ -22,14 +22,46 @@
       expect(node_modules_files).to be_empty
     end
 
+    it "excludes JavaScript package source" do
+      package_files = gemspec.files.select { |f| f.start_with?("package/") }
+      expect(package_files).to be_empty
+    end
+
+    it "excludes repository-only documentation and test files" do
+      excluded_files = gemspec.files.select { |f| f.start_with?("docs/", "test/") }
+      expect(excluded_files).to be_empty
+    end
+
     it "includes lib directory" do
       lib_files = gemspec.files.select { |f| f.start_with?("lib/") }
       expect(lib_files).not_to be_empty
     end
 
+    it "includes install assets needed by shakapacker:install" do
+      expect(gemspec.files).to include(
+        "lib/install/template.rb",
+        "lib/install/application.js",
+        "lib/install/package.json",
+        "lib/install/config/shakapacker.yml",
+        "lib/install/bin/shakapacker",
+        "lib/install/bin/shakapacker-dev-server"
+        "lib/install/bin/shakapacker",
+        "lib/install/bin/shakapacker-dev-server",
+        "lib/install/config/rspack/rspack.config.js",
+        "lib/install/config/rspack/rspack.config.ts",
+        "lib/install/config/webpack/webpack.config.js",
+        "lib/install/config/webpack/webpack.config.ts"
+    end
+
     it "includes RBS type signatures" do
       rbs_files = gemspec.files.select { |f| f.end_with?(".rbs") }
       expect(rbs_files).not_to be_empty
     end
   end
+
+  describe "s.test_files" do
+    it "is empty" do
+      expect(gemspec.test_files).to be_empty
+    end
+  end
 end