Improve server process cleanup and readiness checks

- Add process group management for better child process cleanup
- Add warning logging when process group kill fails with EPERM
- Improve server readiness check to accept only 200-399 HTTP status codes
- Reject 404 and 5xx responses as "not ready" for more reliable health checks

These improvements provide better debugging visibility and reduce flaky tests
by ensuring the server is truly ready before running tests.

Fixes #198

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

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

Author: justin808

lib/cypress_on_rails/server.rb

@@ -1,6 +1,7 @@
 require 'socket'
 require 'timeout'
 require 'fileutils'
+require 'net/http'
 require 'cypress_on_rails/configuration'
 
 module CypressOnRails
@@ -105,30 +106,54 @@ def spawn_server
 
       puts "Starting Rails server: #{server_args.join(' ')}"
 
-      spawn(*server_args, out: $stdout, err: $stderr)
+      @server_pid = spawn(*server_args, out: $stdout, err: $stderr, pgroup: true)
+      @server_pgid = Process.getpgid(@server_pid)
+      @server_pid
     end
 
     def wait_for_server(timeout = 30)
       Timeout.timeout(timeout) do
         loop do
-          begin
-            TCPSocket.new(host, port).close
-            break
-          rescue Errno::ECONNREFUSED, Errno::EHOSTUNREACH
-            sleep 0.1
-          end
+          break if server_responding?
+          sleep 0.1
         end
       end
     rescue Timeout::Error
       raise "Rails server failed to start on #{host}:#{port} after #{timeout} seconds"
     end
 
+    def server_responding?
+      url = "http://#{host}:#{port}"
+      response = Net::HTTP.get_response(URI(url))
+      # Accept 200-399 (success and redirects), reject 404 and 5xx
+      (200..399).cover?(response.code.to_i)
+    rescue Errno::ECONNREFUSED, Errno::EADDRNOTAVAIL, SocketError
+      false
+    end
+
     def stop_server(pid)
-      if pid
-        puts "Stopping Rails server (PID: #{pid})"
-        Process.kill('TERM', pid)
-        Process.wait(pid)
+      return unless pid
+
+      puts "Stopping Rails server (PID: #{pid})"
+      send_term_signal
+      Process.wait(pid)
+    rescue Errno::ESRCH
+      # Process already terminated
+    end
+
+    def send_term_signal
+      if @server_pgid
+        Process.kill('TERM', -@server_pgid)
+      else
+        safe_kill_process('TERM', @server_pid)
       end
+    rescue Errno::ESRCH, Errno::EPERM => e
+      puts "Warning: Failed to kill process group #{@server_pgid}: #{e.message}, trying single process"
+      safe_kill_process('TERM', @server_pid)
+    end
+
+    def safe_kill_process(signal, pid)
+      Process.kill(signal, pid) if pid
     rescue Errno::ESRCH
       # Process already terminated
     end