Fix gem install: serial mruby build and post-install message

Force -j1 on mruby build to avoid race condition where presym
generation recreates directories during parallel CC compilation.
Add post-install message.

Author: bradgessler

enclave.gemspec

@@ -25,6 +25,8 @@ Gem::Specification.new do |spec|
   spec.require_paths = ["lib"]
   spec.extensions = ["ext/enclave/extconf.rb"]
 
+  spec.post_install_message = "Enclave installed! Sandboxed Ruby for AI agents is ready to go."
+
   spec.add_dependency "rake-compiler", "~> 1.2"
 
   spec.add_development_dependency "rspec", "~> 3.0"

ext/enclave/extconf.rb

@@ -9,7 +9,7 @@
 # Build mruby from source
 unless File.exist?(File.join(mruby_build_dir, "lib", "libmruby.a"))
   puts "Building mruby..."
-  system("cd #{mruby_dir} && MRUBY_CONFIG=#{build_config} rake -f #{mruby_dir}/Rakefile") || abort("mruby build failed")
+  system("cd #{mruby_dir} && MRUBY_CONFIG=#{build_config} rake -f #{mruby_dir}/Rakefile -j1") || abort("mruby build failed")
 end
 
 # mruby headers (only used by sandbox_core.c, not enclave.c)