PC3: checkpoint runner starts a dedicated server for the network-client smoke

smoke_test_network_client.gd needs a separate `godot scenes/server.tscn`
process on ENet 7777; the runner never started one, so that test has been
failing in every checkpoint run (the only failure in an otherwise-green
suite). Start it just for that test, tear it down after.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015jtxAiu5dAW4WxCNdGkrkJ

scripts/run_checkpoint_tests.py

@@ -133,9 +133,28 @@ def main():
                 for test in smoke_tests:
                     rel = os.path.relpath(test, ROOT)
                     print(f"\n--- {rel} ---")
+                    # smoke_test_network_client.gd needs a separate dedicated
+                    # server process listening on ENet 7777 -- stand one up
+                    # just for that test and tear it down after.
+                    game_server = None
+                    if os.path.basename(rel) == "smoke_test_network_client.gd":
+                        print("(starting scenes/server.tscn for the network client test)")
+                        game_server = subprocess.Popen(
+                            [godot_bin, "--headless", "--path", str(ROOT), "res://scenes/server.tscn"],
+                            env=godot_env,
+                        )
+                        time.sleep(3)
+                    try:
                         r = run([godot_bin, "--headless", "--path", str(ROOT), "--script", f"res://{rel}"], env=godot_env)
                         if r.returncode != 0:
                             godot_ok = False
+                    finally:
+                        if game_server is not None:
+                            game_server.terminate()
+                            try:
+                                game_server.wait(timeout=10)
+                            except subprocess.TimeoutExpired:
+                                game_server.kill()
                 results["godot smoke tests"] = godot_ok
         finally:
             server_proc.terminate()