port(2P step 3c): stage python27.zip into the mobile sandbox

CPython opens the stdlib zip with its own stdio, so it needs a real path.
On the desktop res:// is a directory and globalize_path() is enough; in an
exported build res:// is inside the PCK, which nothing outside Godot reads.

  make_stdlib_zip.py now also writes <out>.sha256
  mtpython_stdlib_project copies python27.zip + .sha256 into project/
    (gitignored), and both export presets' include_filter lists them, so
    they enter the PCK — checked with --export-pack
  extension/src/python_stdlib.{h,cpp} (Metin2Python.stdlib_path in
    GDScript): reads the bytes out of the PCK, writes
    user://python27.zip.part, hashes the file as written against the
    shipped digest, then renames. A sandbox copy is reused only when it
    matches, so a first start killed mid-copy and a zip replaced by a new
    build both re-stage instead of feeding zipimport a torn file.
  PythonHost::SetDefaultStdLibPath / DefaultStdLibPath() answer with that
    path ($MT_PYTHON_STDLIB still wins). python_stdlib.cpp is the only unit
    that knows res:// / user://; port_platform stays godot-free.

Also fixes the Windows gate, which step 3b broke: without mtpython the
MinGW build compiled UserInterface/StdAfx.h (it includes ScriptLib/StdAfx.h,
as the original PCH does). port/CMakeLists.txt excludes that header and
PythonPackModule.cpp with ScriptLib, and platform/CMakeLists.txt excludes
platform/ScriptLib/ the same way.

Not done: on-device staging. The macOS test drives the mobile path with
force_stage=true, and nothing in the app boot calls it yet — the
interpreter only starts in the process with 2V0.

gates: python_stdlib_test.gd PASS (in-place path, staging, sha256, bytes
equal res://, no .part, ZIPReader finds encodings/__init__.py, no re-copy
on a second call, corrupted copy re-staged) · macOS ctest 27/27 ·
mingw + android + ios port_platform compile clean · port_map.py check 0
errors · key leak check 8/8 none.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

extension/src/python_stdlib.cpp

@@ -0,0 +1,127 @@
+#include "python_stdlib.h"
+
+#include <godot_cpp/classes/dir_access.hpp>
+#include <godot_cpp/classes/file_access.hpp>
+#include <godot_cpp/classes/project_settings.hpp>
+#include <godot_cpp/core/class_db.hpp>
+#include <godot_cpp/variant/utility_functions.hpp>
+
+#include <string>
+
+#ifdef MTGODOT_HAVE_PYTHON
+#include "platform/ScriptLib/PythonHost.h"
+#endif
+
+using namespace godot;
+
+namespace mtgodot {
+
+namespace {
+
+// Both ship in the PCK; the build copies them next to project.godot (extension/CMakeLists.txt).
+constexpr const char *ZIP_RES = "res://python27.zip";
+constexpr const char *SHA_RES = "res://python27.zip.sha256";
+constexpr const char *ZIP_USER = "user://python27.zip";
+constexpr const char *ZIP_USER_TMP = "user://python27.zip.part";
+
+// std::string, not String: this lives at file scope and a godot::String's constructor would run at
+// dlopen time, before the extension's bindings exist.
+std::string g_last_error;
+
+String fail(String *error, const String &text) {
+	g_last_error = text.utf8().get_data();
+	if (error) {
+		*error = text;
+	}
+	return String();
+}
+
+String expected_sha() {
+	if (!FileAccess::file_exists(SHA_RES)) {
+		return String();
+	}
+	return FileAccess::get_file_as_string(SHA_RES).strip_edges();
+}
+
+} // namespace
+
+String stage_python_stdlib(String *error, bool force_stage) {
+	g_last_error.clear();
+	if (error) {
+		*error = String();
+	}
+	if (!FileAccess::file_exists(ZIP_RES)) {
+		return fail(error, String("no ") + ZIP_RES +
+								   " (build with -DMTGODOT_EMBED_PYTHON=ON, which copies it into project/)");
+	}
+
+	ProjectSettings *settings = ProjectSettings::get_singleton();
+	// Desktop and the editor: res:// is a directory on disk, so CPython can open the file in place and
+	// nothing is copied. In an exported game globalize_path() returns a path next to the executable
+	// that does not exist, which is exactly the case the staging below is for.
+	const String in_place = settings->globalize_path(ZIP_RES);
+	if (!force_stage && !in_place.begins_with("res://") && FileAccess::file_exists(in_place)) {
+		return in_place;
+	}
+
+	const String want = expected_sha();
+	if (want.is_empty()) {
+		return fail(error, String("no ") + SHA_RES + " beside the stdlib zip");
+	}
+
+	// An already-staged copy is reused only when it is the zip this build ships: a new version of the
+	// app brings a new digest, and a first start that was killed mid-copy leaves a short file.
+	if (FileAccess::file_exists(ZIP_USER) && FileAccess::get_sha256(ZIP_USER) == want) {
+		return settings->globalize_path(ZIP_USER);
+	}
+
+	const PackedByteArray data = FileAccess::get_file_as_bytes(ZIP_RES);
+	if (data.is_empty()) {
+		return fail(error, String("cannot read ") + ZIP_RES);
+	}
+	{
+		Ref<FileAccess> out = FileAccess::open(ZIP_USER_TMP, FileAccess::WRITE);
+		if (out.is_null()) {
+			return fail(error, String("cannot write ") + ZIP_USER_TMP + ": " +
+									   itos((int) FileAccess::get_open_error()));
+		}
+		out->store_buffer(data);
+		out->close();
+	}
+	// Hash the file as written, not the buffer: a full disk reports itself here and not later as a
+	// zipimport failure three imports into system.py.
+	if (FileAccess::get_sha256(ZIP_USER_TMP) != want) {
+		DirAccess::remove_absolute(ZIP_USER_TMP);
+		return fail(error, String("staged ") + ZIP_USER + " does not match " + want);
+	}
+	if (FileAccess::file_exists(ZIP_USER)) {
+		DirAccess::remove_absolute(ZIP_USER);
+	}
+	if (DirAccess::rename_absolute(ZIP_USER_TMP, ZIP_USER) != OK) {
+		return fail(error, String("cannot rename ") + ZIP_USER_TMP + " to " + ZIP_USER);
+	}
+	UtilityFunctions::print("[python27] staged ", ZIP_USER, " (", data.size(), " bytes, sha256 ", want, ")");
+	return settings->globalize_path(ZIP_USER);
+}
+
+String Metin2Python::stdlib_path(bool force_stage) {
+	const String path = stage_python_stdlib(nullptr, force_stage);
+#ifdef MTGODOT_HAVE_PYTHON
+	if (!path.is_empty()) {
+		PythonHost::SetDefaultStdLibPath(path.utf8().get_data());
+	}
+#endif
+	return path;
+}
+
+String Metin2Python::last_error() {
+	return String::utf8(g_last_error.c_str());
+}
+
+void Metin2Python::_bind_methods() {
+	ClassDB::bind_static_method("Metin2Python", D_METHOD("stdlib_path", "force_stage"),
+							   &Metin2Python::stdlib_path, DEFVAL(false));
+	ClassDB::bind_static_method("Metin2Python", D_METHOD("last_error"), &Metin2Python::last_error);
+}
+
+} // namespace mtgodot