2V0-f: run the real system.py app loop in Godot

- system.py runs app.Loop() on the script fiber; each UIUpdate is one
  CPythonApplication::Process(). Logo -> Login, popup ESC/click and
  app.Exit teardown (launcher cleared first, as in 40250 Main) work.
- Image commands are base-texture quads with UVs (a .sub shares its parent
  texture); ImageInstance/ExpandedImageInstance OnRender and SetRenderingRect
  ported verbatim, so scale/rotation/rendering rect are drawn.
- CGraphicBase::GetColor / grp.GenerateColor ported (ThinBoard background).
- port.app_loop test, python_host_test app-loop checks, MT_TEST_MODE=python_ui.
- TODO: .fnt/CGraphicText font pipeline, ExpandedImage blend modes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

extension/src/platform/ScriptLib/PythonBoot.cpp

@@ -5,12 +5,16 @@
 #include "ScriptLib/Resource.h"
 #include "UserInterface/StdAfx.h" // initpack and the rest of the module initializer list
 #include "EterPythonLib/StdAfx.h"
+#include "EterBase/Timer.h"
 #include "PythonBoot.h"
 #include "PythonHost.h"
 #include "../EterLib/UIRenderCommands.h"
 #include "../EterBase/LogBox.h"
 
+#include <condition_variable>
 #include <memory>
+#include <mutex>
+#include <pthread.h>
 
 namespace
 {
@@ -18,6 +22,8 @@ namespace
 std::unique_ptr<CPythonLauncher> g_launcher;
 std::unique_ptr<UI::CWindowManager> g_window_manager;
 std::unique_ptr<CPythonResource> g_resource;
+// 40250 CPythonApplication::m_timer; CSlotWindow's cool time and Process() read it via Instance().
+std::unique_ptr<CTimer> g_timer;
 
 bool fail(std::string* error, const std::string& text)
 {
@@ -25,6 +31,78 @@ bool fail(std::string* error, const std::string& text)
 		*error = text;
 	return false;
 }
+
+// PORT: 40250 RunApp() blocks inside app.Loop() (CPythonApplication::Loop, PythonApplication.cpp:980)
+// and only returns to run mainStream.Destroy() when the window closes. Godot owns the frame loop here,
+// so system.py runs on its own thread and the two threads pass a baton: exactly one of them runs at
+// any time. Loop() hands the baton back after every Process(), and the host hands it over once per
+// Godot frame (AppFrame). The script keeps its original control flow — including the code after
+// app.Loop() — without ever blocking the Godot main thread for more than one Process().
+struct ScriptFiber
+{
+	enum Turn { Host, Script };
+
+	std::mutex mutex;
+	std::condition_variable cv;
+	Turn turn = Host;
+	pthread_t thread{};
+	bool alive = false;       // the thread exists and has not been joined
+	bool finished = false;    // RunMainScript's body returned
+	bool looping = false;     // parked inside CPythonApplication::Loop
+	bool quit = false;        // app.Exit / app.Abort / Stop
+	bool ok = false;
+	std::string error;
+	std::string command_line;
+};
+ScriptFiber g_fiber;
+thread_local bool t_on_fiber = false;
+
+// Caller holds the GIL. Returns with the GIL held again after the script has given the baton back.
+void hand_to_script()
+{
+	PyThreadState* state = PyEval_SaveThread();
+	{
+		std::unique_lock<std::mutex> lock(g_fiber.mutex);
+		g_fiber.turn = ScriptFiber::Script;
+		g_fiber.cv.notify_all();
+		g_fiber.cv.wait(lock, [] { return g_fiber.turn == ScriptFiber::Host; });
+	}
+	PyEval_RestoreThread(state);
+}
+
+void join_fiber()
+{
+	if (!g_fiber.alive)
+		return;
+	PyThreadState* state = PyEval_SaveThread();
+	pthread_join(g_fiber.thread, nullptr);
+	PyEval_RestoreThread(state);
+	g_fiber.alive = false;
+}
+
+bool run_main_script_body(const char* lpCmdLine, std::string* error);
+
+void* fiber_main(void*)
+{
+	{
+		std::unique_lock<std::mutex> lock(g_fiber.mutex);
+		g_fiber.cv.wait(lock, [] { return g_fiber.turn == ScriptFiber::Script; });
+	}
+	t_on_fiber = true;
+	PyGILState_STATE gil = PyGILState_Ensure();
+	std::string error;
+	const bool ok = run_main_script_body(g_fiber.command_line.c_str(), &error);
+	PyGILState_Release(gil);
+
+	std::lock_guard<std::mutex> lock(g_fiber.mutex);
+	g_fiber.ok = ok;
+	g_fiber.error = error;
+	g_fiber.finished = true;
+	g_fiber.looping = false;
+	g_fiber.turn = ScriptFiber::Host;
+	g_fiber.cv.notify_all();
+	return nullptr;
+}
 }
 
 void init_2v0_gameplay_stubs();
@@ -63,20 +141,32 @@ void UIMouseButton(int button, bool pressed, int x, int y)
 	}
 }
 
+// 40250 CPythonApplication::OnKeyDown/OnKeyUp (PythonApplicationEvent.cpp:130-146): ESC first goes
+// to RunPressEscapeKey (the OnPressEscapeKey chain every dialog closes on), then to RunKeyDown.
 void UIKey(int key, bool pressed)
 {
 	if (!g_window_manager) return;
-	if (pressed) g_window_manager->RunKeyDown(key);
-	else g_window_manager->RunKeyUp(key);
+	if (pressed)
+	{
+		if (DIK_ESCAPE == key)
+			g_window_manager->RunPressEscapeKey();
+		g_window_manager->RunKeyDown(key);
+	}
+	else
+		g_window_manager->RunKeyUp(key);
 }
 
 void UIUpdate()
 {
+	// While system.py is inside app.Loop(), one host frame is one CPythonApplication::Process(),
+	// which updates and renders the window tree itself.
+	if (IsAppLooping()) { AppFrame(); return; }
 	if (g_window_manager) g_window_manager->Update();
 }
 
 void UIRender()
 {
+	if (IsAppLooping()) return;
 	UIRenderBeginFrame();
 	if (g_window_manager) g_window_manager->Render();
 }
@@ -94,6 +184,8 @@ bool Start(const char* stdlib_path, std::string* error)
 	PythonHost::Configure();
 
 	g_launcher = std::make_unique<CPythonLauncher>(); // Py_Initialize
+	// The script fiber (RunMainScript) is a second OS thread; 2.7 creates the GIL lazily.
+	PyEval_InitThreads();
 	if (!g_launcher->Create())
 	{
 		Stop();
@@ -106,17 +198,19 @@ bool Start(const char* stdlib_path, std::string* error)
 		Stop();
 		return fail(error, "InstallStdLib(" + stdlib + "): " + stdlib_error);
 	}
+	g_timer = std::make_unique<CTimer>();
 	g_resource = std::make_unique<CPythonResource>();
 	g_window_manager = std::make_unique<UI::CWindowManager>();
 	return true;
 }
 
-// 40250: RunMainScript
-bool RunMainScript(const char* lpCmdLine, std::string* error)
-{
-	if (!g_launcher)
-		return fail(error, "PythonBoot::Start has not run");
+}
 
+namespace
+{
+// Mirrors 40250 RunMainScript. Runs on the script fiber.
+bool run_main_script_body(const char* lpCmdLine, std::string* error)
+{
 	CPythonLauncher& pyLauncher = *g_launcher;
 
 	// The module initializers follow 40250's order; missing modules arrive in later 2V steps.
@@ -189,6 +283,81 @@ bool RunMainScript(const char* lpCmdLine, std::string* error)
 	NANOEND
 	return true;
 }
+}
+
+namespace PythonBoot
+{
+
+bool RunMainScript(const char* lpCmdLine, std::string* error)
+{
+	if (!g_launcher)
+		return fail(error, "PythonBoot::Start has not run");
+	if (g_fiber.alive)
+		return fail(error, "RunMainScript is already running");
+
+	g_fiber.turn = ScriptFiber::Host;
+	g_fiber.finished = g_fiber.looping = g_fiber.quit = g_fiber.ok = false;
+	g_fiber.error.clear();
+	g_fiber.command_line = lpCmdLine ? lpCmdLine : "";
+
+	// 40250's main thread has the default 1 MB Windows stack; Python frames are deep during
+	// uiScriptLocale/ui imports, so give the script thread more than a secondary thread's default.
+	pthread_attr_t attr;
+	pthread_attr_init(&attr);
+	pthread_attr_setstacksize(&attr, 16u * 1024u * 1024u);
+	const int rc = pthread_create(&g_fiber.thread, &attr, fiber_main, nullptr);
+	pthread_attr_destroy(&attr);
+	if (rc != 0)
+		return fail(error, "cannot start the script thread");
+	g_fiber.alive = true;
+
+	hand_to_script(); // until system.py parks in app.Loop() or returns
+	if (g_fiber.finished)
+	{
+		join_fiber();
+		if (!g_fiber.ok)
+			return fail(error, g_fiber.error);
+	}
+	return true;
+}
+
+bool IsAppLooping()
+{
+	return g_fiber.alive && g_fiber.looping && !g_fiber.finished;
+}
+
+bool AppFrame()
+{
+	if (!IsAppLooping())
+		return false;
+	hand_to_script();
+	if (g_fiber.finished)
+		join_fiber();
+	return IsAppLooping();
+}
+
+bool AppLoopWait()
+{
+	if (!t_on_fiber)
+		return false;
+	g_fiber.looping = true;
+	if (g_fiber.quit)
+		return false;
+	PyThreadState* state = PyEval_SaveThread();
+	{
+		std::unique_lock<std::mutex> lock(g_fiber.mutex);
+		g_fiber.turn = ScriptFiber::Host;
+		g_fiber.cv.notify_all();
+		g_fiber.cv.wait(lock, [] { return g_fiber.turn == ScriptFiber::Script; });
+	}
+	PyEval_RestoreThread(state);
+	return !g_fiber.quit;
+}
+
+void AppRequestQuit()
+{
+	g_fiber.quit = true;
+}
 
 bool RunLine(const char* source, std::string* error)
 {
@@ -205,9 +374,21 @@ void Stop()
 {
 	if (!g_launcher)
 		return;
+	// In 40250, closing the window ends Loop(); RunApp() then runs mainStream.Destroy() and returns.
+	if (g_fiber.alive)
+	{
+		AppRequestQuit();
+		while (g_fiber.alive && !g_fiber.finished)
+			hand_to_script();
+		join_fiber();
+	}
+	g_fiber.finished = false;
+	// 40250 Main(): pyLauncher.Clear() runs before app->Destroy()/delete app, so the window manager
+	// (a CPythonApplication member) is still alive while Py_Finalize runs the windows' __del__.
+	g_launcher->Clear();
 	g_window_manager.reset();
 	g_resource.reset();
-	g_launcher->Clear(); // Main() calls Clear() explicitly before the launcher leaves scope
+	g_timer.reset();
 	g_launcher.reset();
 }