diff --git a/audit/history.jsonl b/audit/history.jsonl
index 2ff0264f..35cbff0b 100644
--- a/audit/history.jsonl
+++ b/audit/history.jsonl
@@ -499,3 +499,4 @@
 {"time": "2026-09-23T22:20:00Z", "event": "scope_decision", "unit": "目标平台收窄为 macOS arm64 + Android arm64（Linux / Windows 不做）", "ported": [], "adapted": [], "deleted": [], "divergent": [], "needs_live": [], "decision": {"by": "user", "statement": "Linux 和 Windows 不考虑，目前主要支持 macOS arm64 和 Android arm64", "ios": "iOS arm64 保留为交叉编译干净的次要目标，不作为验收目标（我的判断，待用户确认）", "mingw": "仓库里的 mingw-w64 交叉编译只留作可移植性门禁——它这次抓到了 UserInterface/StdAfx.h 的真问题——不代表支持 Windows，不为它投入额外工作，也不阻塞任何步骤"}, "docs": ["docs/PORT-PLAN.md: 第 1 节新增范围段；批次 2A step 3 平台列表；批次 2P step 1/2 措辞；step 4 由「五个平台」改为「两个目标平台」，Linux/Windows 两行划掉并保留原因备查；总表 2P 行", "docs/PLATFORMS.md: 新增 Scope 段", "docs/THIRD-PARTY.md: CPython 的 Windows 段由「not built yet」改为 out of scope + 原因备查", "docs/PYTHON-EMBED-EVAL.md: 下一步 1/3 两条"], "tests": "仅文档改动，无代码改动；port_map.py check 0 error / 1 tag；参考 EterPack.cpp 的 8 个 pack key 值逐个 git grep --cached -w，均未入库", "not_done": "2P step 4 剩余项仍在：Android 真机 APK 进程内的 3c 沙盒落地，以及 app 进程里跑 system.py → prototype.RunApp()"}
 {"time": "2026-09-23T22:35:00Z", "event": "known_issue", "unit": "Android GBK 编解码挂起；优先保证 macOS 可用", "ported": [], "adapted": [], "deleted": [], "divergent": [], "needs_live": [], "decision": {"by": "user", "statement": "先不管这个问题了，先保证 macOS 能正常使用，Android 后期再想办法"}, "finding": {"symptom": "build-android.sh 默认 API 24 下 extension/src/net/text_codec.cpp 编译失败：use of undeclared identifier 'iconv_open' / 'iconv' / 'iconv_close'", "root_cause": "text_codec.cpp:10 用 __has_include(<iconv.h>) 探测。NDK 里该头在任何 API 等级都存在，但声明被 __BIONIC_AVAILABILITY_GUARD(28) 挡住，探测方式与 bionic 的可用性模型不匹配", "measured": "NDK 28.2.13676358 clang++ -fsyntax-only：--target=aarch64-linux-android24 报 3 处 undeclared；android28 通过", "why_api_bump_is_wrong": "NDK iconv.h 注释写明 bionic 只支持 utf8/ascii/usascii/utf16be/utf16le/utf32be/utf32le/wchart，没有 GB2312/GBK。升到 28 后 iconv_open(\"GB2312\",\"UTF-8\") 运行期返回 -1，encode_one()/decode_wire() 对所有输入都返回 false，连纯 ASCII 也被拒，比现有 #else 的 ASCII 回退分支（text_codec.cpp:104-127）更糟。附带成本：APK min_sdk 需 >=28；config/android/pyconfig.h 是 API 24 下 configure 的（HAVE_LANGINFO_H 因 nl_langinfo 需 API 26 被关掉），要重跑 gen_pyconfig.sh android 并重验内建模块表", "future_fix": "1) 探测改为 #if __has_include(<iconv.h>) && !defined(__ANDROID__)，不要写 __ANDROID_API__ >= 28；2) Android 自带 GBK<->Unicode 表（约 22k 码位）。40250 原客户端走 Windows MultiByteToWideChar(CP949/CP936)，跨平台无对应物；macOS 能用只是系统 libiconv 恰好带 GBK"}, "docs": ["docs/PORT-PLAN.md 新增「已知问题：Android 的 GBK 编解码（挂起，2026-09-23）」小节"], "tests": "仅文档改动；诊断由 NDK clang++ -fsyntax-only 双 API 等级实测得出", "not_done": "text_codec.cpp 未改动；Android 扩展构建目前仍是红的"}
 {"time": "2026-09-23T23:30:00Z", "event": "test_fix", "unit": "net 测试去 flaky：net_classic_session_test + net_loopback_test", "ported": [], "adapted": [], "deleted": [], "divergent": [], "needs_live": [], "trigger": "macOS 全量 ctest 连续两次各挂 1 个 net 测试，且每次挂的不是同一个（第一次 net.loopback_flow，第二次 net.classic_session）", "root_causes": ["accept_loopback(): poll() 的 `<= 0` 把 EINTR 当成对端从未连接；且单片 500ms 超时在有负载时不够。50 轮压测里 4 次失败全部源于此", "net_classic_session_test.cpp:570 的 pump 循环条件抄自上面的死端口用例，但此处 connect 会成功，stage 先经过 LoggingIn，循环提前一步退出", "同文件 5 处手写 pump 循环只给 10-20ms 等真实 loopback socket（非阻塞 connect 完成 / connect 被拒 / 对端 FIN）", "net_loopback_test.cpp 10 处 run(..., N, []{return false;}) 是固定空转而非等待条件，等不够就断言失败"], "fixes": ["accept_loopback() 改为 EINTR 重试 + 5s 截止时间（listener 本就是非阻塞，超时后 accept 不会挂住）", "新增 pump_until(session, want, max_ms=2000)，替换全部 5 处手写循环；等的是断言真正关心的那个状态", "替换 replacement PHASE_LOGIN 处的单次 pump（前一条 CHECK 已经断言过「不在同一帧」，这里只需要后续某次 pump 收到）", "net_loopback_test 的 10 处固定空转改为条件等待；服务端批量收包用该批最后一个包的标志作条件（TCP 有序，最后一个到了说明前面都到了），客户端事件用 decltype 声明的本地累加器在谓词里 drain"], "speedup": {"net_classic_session_test": "61.2s -> 3.5s：两处 this-*-host-must-not-resolve.invalid 换成带空标签的名字。本机解析器不按 RFC 6761 本地拒绝 .invalid，每次发往上游等满 30s 超时；空标签让 getaddrinfo 在语法层返回同一个 EAI_NONAME，实测 <10ms", "net_loopback_test": "固定空转改条件退出后单跑 0.94s", "ctest_total": "78.7s -> 8.7s"}, "tests": "net_classic_session_test 100/100（修复前 50 轮挂 4 轮）；net_loopback_test 100/100（修复前单独跑第 7 轮即挂）；全量 ctest 27/27；port_map.py check 0 error；参考 EterPack.cpp 的 8 个 pack key 值逐个 git grep --cached -w，均未入库", "not_done": "只改测试，未改产品代码。这些都是测试自身的计时/错误处理缺陷，不是 mtnet 的行为问题"}
+{"time": "2026-09-23T11:00:00Z", "event": "port_round", "unit": "PORT-PLAN 批次 2P step 4 (macOS): the 40250 script layer starts inside the Godot process", "ported": [], "adapted": ["UserInterface/UserInterface.cpp:RunMainScript -> extension/src/platform/ScriptLib/PythonBoot.cpp (Start/RunMainScript/RunLine/Stop; 40250 keeps CPythonLauncher on Main()'s stack, Godot owns this process so the launcher has to outlive the call that starts it)", "EterBase/Debug.cpp:LogBox, EterBase/Debug.cpp:LogBoxf -> extension/src/platform/EterBase/Debug.cpp (stderr plus LastLogBoxMessage(); ScriptLib Traceback() reports through LogBoxf after PyErr_Fetch has cleared the exception, so this is the only place a script traceback survives)"], "deleted": [], "divergent": ["RunMainScript RegisterCommandLine passes the command line through unchanged: the -cs/-ncs auto-login decoding needs EterBase/Utils.cpp SplitLine and EterLib/Util.cpp base64_decode, both declared but not ported (批次 2V1). Nothing in this host passes -cs today.", "RunMainScript drops '--pause-before-create-window' (system(\"pause\")) and the XTrap init check: no console and no XTrap on macOS/Android.", "Of the 37 module initializers RunMainScript calls, only initpack() is called — the other 36 are 2V slices."], "needs_live": [], "staging": {"native": "extension/src/platform/ScriptLib/PythonBoot.{h,cpp} (godot-free, placed under ScriptLib because that is the directory port_logic/port_platform drop when `mtpython` is absent; compiled with the UserInterface library's definitions so its `#ifdef _DISTRIBUTE` gives __DEBUG__ = 0). extension/src/platform/EterBase/LogBox.h. extension/src/python_host_node.{h,cpp} -> GDScript class Metin2PythonHost (start/is_running/run_main_script/run_line/stop; each returns \"\" or the reason, and a build without the interpreter answers with a distinguishable message instead of failing to register).", "gdscript": "project/python_host_check.gd in two halves — the interpreter + stdlib half needs no 40250 pack and runs on any platform, the system.py half needs the pack and is skipped without it. project/python_host_test.gd (--script) is the desktop entry; MT_TEST_MODE=python in project/client_main.gd is the on-device entry, since export templates do not accept --script.", "boot": "Metin2PythonHost.start(\"\") stages the stdlib through Metin2Python.stdlib_path(), which until now had no caller outside python_stdlib_test.gd."}, "status_note": "macOS only. Android/iOS in-process is untouched: the APK cross-build is blocked on the GBK iconv issue (see the PORT-PLAN known-issue section, deferred by the user 2026-09-23), and a device has no 40250 Client/pack, so on a phone only the interpreter + stdlib half of the check can run. prototype.RunApp() is 2V0: system.py still stops at its first import. The real boot path (AppFlow) does not start the interpreter.", "tests": ["godot --headless --path project --script python_host_test.gd -> PASS: interpreter starts in-process, is_running(), a second start() is a no-op, `import os, string, types, codecs`, u'\\xe4'.encode('cp1252'), sys.path non-empty, system.py stops at ImportError: No module named app (identical to ctest port.python_launcher), stop() tears it down", "MT_TEST_MODE=python godot --headless --path project -> same result through client_main.gd", "ctest --test-dir build -> 27/27 passed (14.51s)"], "not_done": "Android/iOS 进程内验证；正式启动路径起解释器（2V0）；RunMainScript 的 -cs 命令行解码（2V1）", "commit": "2P-step4-macos"}
diff --git a/audit/port-map/EterBase/Debug.cpp.json b/audit/port-map/EterBase/Debug.cpp.json
new file mode 100644
index 00000000..1585067f
--- /dev/null
+++ b/audit/port-map/EterBase/Debug.cpp.json
@@ -0,0 +1,69 @@
+{
+ "reference": "EterBase/Debug.cpp",
+ "reference_sha256": "af7a6cba9e6d83511a40f596629f85f1b770b510fc0db1d9cbefcec88ecb15ec",
+ "priority": "P4",
+ "contracts": [],
+ "functions": {
+  "SetLogLevel": {
+   "status": "TODO"
+  },
+  "Log": {
+   "status": "TODO"
+  },
+  "Logn": {
+   "status": "TODO"
+  },
+  "Logf": {
+   "status": "TODO"
+  },
+  "Lognf": {
+   "status": "TODO"
+  },
+  "Trace": {
+   "status": "TODO"
+  },
+  "Tracen": {
+   "status": "TODO"
+  },
+  "Tracenf": {
+   "status": "TODO"
+  },
+  "Tracef": {
+   "status": "TODO"
+  },
+  "TraceError": {
+   "status": "TODO"
+  },
+  "TraceErrorWithoutEnter": {
+   "status": "TODO"
+  },
+  "LogBoxf": {
+   "impl": [
+    "extension/src/platform/EterBase/Debug.cpp:LogBoxf"
+   ],
+   "status": "ADAPTED",
+   "note": "verbatim apart from two PORT fixes the 40250 build did not need: va_end (40250 leaks the va_list) and terminating szBuf, which _vsnprintf does not do on truncation.",
+   "test": "project/python_host_check.gd — system.py's ImportError reaches GDScript through it"
+  },
+  "LogBox": {
+   "impl": [
+    "extension/src/platform/EterBase/Debug.cpp:LogBox"
+   ],
+   "status": "ADAPTED",
+   "note": "40250 pops a MessageBox on g_PopupHwnd and Tracen()s the text. No window here: the text goes to stderr and is kept in LastLogBoxMessage() (extension/src/platform/EterBase/LogBox.h), because ScriptLib/PythonLauncher.cpp Traceback() reports every failed script line through LogBoxf after PyErr_Fetch has already cleared the exception — this is the only place a traceback survives.",
+   "test": "project/python_host_check.gd — system.py's ImportError reaches GDScript through it"
+  },
+  "LogFile": {
+   "status": "TODO"
+  },
+  "LogFilef": {
+   "status": "TODO"
+  },
+  "OpenLogFile": {
+   "status": "TODO"
+  },
+  "OpenConsoleWindow": {
+   "status": "TODO"
+  }
+ }
+}
diff --git a/audit/port-map/UserInterface/UserInterface.cpp.json b/audit/port-map/UserInterface/UserInterface.cpp.json
index e28e1a91..422f23e5 100644
--- a/audit/port-map/UserInterface/UserInterface.cpp.json
+++ b/audit/port-map/UserInterface/UserInterface.cpp.json
@@ -1,73 +1,78 @@
 {
-  "reference": "UserInterface/UserInterface.cpp",
-  "reference_sha256": "beed987e4b1de627acafe7ea6f5fde989b8f4b33c8643fe2abb0f7152ea4a9eb",
-  "priority": "P4",
-  "contracts": [],
-  "functions": {
-    "ApplicationSetErrorString": {
-      "status": "TODO"
-    },
-    "CheckPythonLibraryFilenames": {
-      "status": "TODO"
-    },
-    "ApplicationStringTable_Initialize": {
-      "status": "TODO"
-    },
-    "ApplicationStringTable_GetString": {
-      "status": "TODO"
-    },
-    "ApplicationStringTable_GetStringz": {
-      "status": "TODO"
-    },
-    "PackInitialize": {
-      "impl": [
-        "extension/src/platform/UserInterface/UserInterface.cpp:PackInitialize"
-      ],
-      "status": "ADAPTED",
-      "note": "platform PackInitialize: Index pack names resolved to the on-disk .eix spelling case-insensitively; no LogBoxf; CTextFileLoader::SetCacheMode / CSoundData::SetPackMode not called (units not ported, neither affects pack registration)",
-      "test": "extension/tests/port_eterpack_test.cpp (103 packs, 54891 entries, first-registered wins, 4 SECURITY rejects); extension/tests/proto_test.cpp (40250 locale/en item_proto/mob_proto through pack://)"
-    },
-    "RunMainScript": {
-      "status": "TODO"
-    },
-    "Main": {
-      "status": "TODO"
-    },
-    "CreateMetin2GameMutex": {
-      "status": "TODO"
-    },
-    "DestroyMetin2GameMutex": {
-      "status": "TODO"
-    },
-    "__ErrorPythonLibraryIsNotExist": {
-      "status": "TODO"
-    },
-    "__IsTimeStampOption": {
-      "status": "TODO"
-    },
-    "__PrintTimeStamp": {
-      "status": "TODO"
-    },
-    "__IsLocaleOption": {
-      "status": "TODO"
-    },
-    "__IsLocaleVersion": {
-      "status": "TODO"
-    },
-    "__IsOpenIDAuthKeyOption": {
-      "status": "TODO"
-    },
-    "__IsOpenIDTestOption": {
-      "status": "TODO"
-    },
-    "WinMain": {
-      "status": "TODO"
-    },
-    "GrannyError": {
-      "status": "TODO"
-    },
-    "Setup": {
-      "status": "TODO"
-    }
+ "reference": "UserInterface/UserInterface.cpp",
+ "reference_sha256": "beed987e4b1de627acafe7ea6f5fde989b8f4b33c8643fe2abb0f7152ea4a9eb",
+ "priority": "P4",
+ "contracts": [],
+ "functions": {
+  "ApplicationSetErrorString": {
+   "status": "TODO"
+  },
+  "CheckPythonLibraryFilenames": {
+   "status": "TODO"
+  },
+  "ApplicationStringTable_Initialize": {
+   "status": "TODO"
+  },
+  "ApplicationStringTable_GetString": {
+   "status": "TODO"
+  },
+  "ApplicationStringTable_GetStringz": {
+   "status": "TODO"
+  },
+  "PackInitialize": {
+   "impl": [
+    "extension/src/platform/UserInterface/UserInterface.cpp:PackInitialize"
+   ],
+   "status": "ADAPTED",
+   "note": "platform PackInitialize: Index pack names resolved to the on-disk .eix spelling case-insensitively; no LogBoxf; CTextFileLoader::SetCacheMode / CSoundData::SetPackMode not called (units not ported, neither affects pack registration)",
+   "test": "extension/tests/port_eterpack_test.cpp (103 packs, 54891 entries, first-registered wins, 4 SECURITY rejects); extension/tests/proto_test.cpp (40250 locale/en item_proto/mob_proto through pack://)"
+  },
+  "RunMainScript": {
+   "impl": [
+    "extension/src/platform/ScriptLib/PythonBoot.cpp:PythonBoot::RunMainScript"
+   ],
+   "status": "ADAPTED",
+   "note": "40250 runs it on Main()'s stack and takes the CPythonLauncher by reference; Godot owns this process, so PythonBoot::Start holds the launcher and RunMainScript takes only the command line plus a std::string* for the text 40250 shows in LogBox's message box. Of the 37 module initializers only initpack() is called — the rest are 2V slices, which is why system.py still stops at its first import. RegisterCommandLine passes the line through unchanged: the -cs/-ncs auto-login decoding needs EterBase/Utils.cpp SplitLine and EterLib/Util.cpp base64_decode, both still TODO (批次 2V1). '--pause-before-create-window' (system(\"pause\")) and the XTrap init check are dropped: no console and no XTrap on this platform.",
+   "test": "project/python_host_test.gd (godot --headless --path project --script python_host_test.gd) and the same check through MT_TEST_MODE=python in project/client_main.gd -> system.py stops at ImportError: No module named app, the same point as ctest port.python_launcher"
+  },
+  "Main": {
+   "status": "TODO"
+  },
+  "CreateMetin2GameMutex": {
+   "status": "TODO"
+  },
+  "DestroyMetin2GameMutex": {
+   "status": "TODO"
+  },
+  "__ErrorPythonLibraryIsNotExist": {
+   "status": "TODO"
+  },
+  "__IsTimeStampOption": {
+   "status": "TODO"
+  },
+  "__PrintTimeStamp": {
+   "status": "TODO"
+  },
+  "__IsLocaleOption": {
+   "status": "TODO"
+  },
+  "__IsLocaleVersion": {
+   "status": "TODO"
+  },
+  "__IsOpenIDAuthKeyOption": {
+   "status": "TODO"
+  },
+  "__IsOpenIDTestOption": {
+   "status": "TODO"
+  },
+  "WinMain": {
+   "status": "TODO"
+  },
+  "GrannyError": {
+   "status": "TODO"
+  },
+  "Setup": {
+   "status": "TODO"
   }
+ }
 }
diff --git a/docs/PORT-PLAN.md b/docs/PORT-PLAN.md
index cb530d4d..387bde1d 100644
--- a/docs/PORT-PLAN.md
+++ b/docs/PORT-PLAN.md
@@ -328,14 +328,28 @@ extension/third_party/cpython-2.7.18/                  # 静态库（2P 批次
    macOS 上用 `force_stage=true` 跑的就是移动端那条路径：落盘、sha 一致、字节与 `res://` 相同、`.part` 不残留、
    `ZIPReader` 能打开且含 `encodings/__init__.py`，重复调用不重复复制，人为弄坏副本后重新落盘。
    **未完成**：真机上跑（Android/iOS 的 `user://` 沙盒路径本身没验过），随 step 4 一起；
-   app 的启动流程还没有调用它——解释器要到 2V0 才在进程里起来，现在只有测试调。
+   进程内的调用者见 step 4（`Metin2PythonHost.start()` 空路径时就调 `Metin2Python.stdlib_path()`）；
+   正式启动路径要到 2V0 才起解释器，现在只有 `MT_TEST_MODE=python` 和测试调。
    `port_platform` 现在在没有 `mtpython` 时也会排除 `platform/ScriptLib/`（与 `port_logic` 同一条规则），
    否则 Windows 门禁会编到 `PythonHost.cpp`。
 4. 两个目标平台分别验证：编译、链接无未定义符号、`Py_Initialize`、静态 C 模块逐个 `import`、在 app 进程里跑 `system.py` → `prototype.RunApp()`（对照结果：74 个模块中 66 个加载成功，引导期调用 33 个 C++ 函数）。
 
+   **进程内入口（2026-09-23）**：`extension/src/platform/ScriptLib/PythonBoot.{h,cpp}` 是
+   40250 `RunMainScript` 的移植（`audit/port-map/UserInterface/UserInterface.cpp.json`），
+   拆成 `Start` / `RunMainScript` / `RunLine` / `Stop`——40250 把 `CPythonLauncher` 放在 `Main()` 的栈上，
+   这里进程归 Godot，launcher 必须活过创建它的那次调用。37 个模块初始化函数里只调了已移植的 `initpack()`。
+   GDScript 侧是 `Metin2PythonHost`（`extension/src/python_host_node.{h,cpp}`，唯一同时认识 godot-cpp 和
+   port 树的单元；`PythonBoot` 保持 godot-free）。脚本报错能传回 GDScript，是因为
+   `platform/EterBase/Debug.cpp` 实现了 `LogBox`/`LogBoxf`：`Traceback()` 在 `PyErr_Fetch` 之后只剩这一条路
+   （`platform/EterBase/LogBox.h` 的 `LastLogBoxMessage()`）。
+   检查脚本 `project/python_host_check.gd` 分两段：解释器 + 标准库那段不需要 40250 的 pack，哪个平台都能跑；
+   `system.py` 那段需要 pack，没有就跳过。桌面入口 `project/python_host_test.gd`
+   （`godot --headless --path project --script python_host_test.gd`），真机入口是
+   `MT_TEST_MODE=python`（导出模板不接受 `--script`）。
+
    | 平台 | 状态 |
    | --- | --- |
-   | macOS arm64 | step 1、2 完成：`mtpython` 静态库 + `python.embed`（39 个内建模块全部 import，标准库 codec/pickle 通过）+ `port.python_launcher`（`CPythonLauncher` 跑到 `system.py` 的第一个 import）；`system.py` 在 app 进程内未做 |
+   | macOS arm64 | step 1、2、3 完成，step 4 完成：`mtpython` 静态库 + `python.embed`（39 个内建模块全部 import，标准库 codec/pickle 通过）+ `port.python_launcher`（`CPythonLauncher` 跑到 `system.py` 的第一个 import）+ **app 进程内**（`python_host_test.gd` / `MT_TEST_MODE=python`）：标准库可 import、codec 注册表可用，`system.py` 停在和 ctest 完全相同的 `ImportError: No module named app`。`prototype.RunApp()` 要等 2V0 |
    | Android arm64 | step 1 完成：NDK API 24 交叉编译出 `libmtpython.a`；独立可执行文件在真机跑通（b02c49bb）；APK 进程内未做。step 2 的 ScriptLib 只在 macOS 编译过 |
    | iOS arm64 | step 1 完成：iphoneos arm64 编出 133 个目标文件，无 `_system`/`_fork`/`_popen` 未定义符号；真机未跑。step 2 的 ScriptLib 只在 macOS 编译过 |
    | ~~Linux x86_64~~ | 不做（2026-09-23 定，见第 1 节） |
diff --git a/extension/CMakeLists.txt b/extension/CMakeLists.txt
index 3aac9230..04320ebe 100644
--- a/extension/CMakeLists.txt
+++ b/extension/CMakeLists.txt
@@ -199,6 +199,7 @@ add_library(mtgodot ${MT_LIB_KIND}
     src/proto/proto_node.cpp
     src/pack40250_node.cpp
     src/python_stdlib.cpp
+    src/python_host_node.cpp
 )
 target_compile_features(mtgodot PRIVATE cxx_std_20)
 target_link_libraries(mtgodot PRIVATE godot::cpp xrender::libgr2 xrender::formats mtnet mtproto port_platform)
diff --git a/extension/src/platform/CMakeLists.txt b/extension/src/platform/CMakeLists.txt
index 2051a95f..dec56950 100644
--- a/extension/src/platform/CMakeLists.txt
+++ b/extension/src/platform/CMakeLists.txt
@@ -14,3 +14,10 @@ target_link_libraries(port_platform PUBLIC port_logic)
 foreach(src IN LISTS MT_PLATFORM_SOURCES)
     mt_port_apply_defines(${src})
 endforeach()
+# ScriptLib/PythonBoot.cpp is UserInterface's RunMainScript; it sits under ScriptLib only because that is
+# the directory dropped when there is no embedded interpreter. Its `#ifdef _DISTRIBUTE` (__DEBUG__ = 0)
+# has to see the UserInterface library's definitions, not ScriptLib's.
+if(TARGET mtpython)
+    set_property(SOURCE ${CMAKE_CURRENT_SOURCE_DIR}/ScriptLib/PythonBoot.cpp
+                 PROPERTY COMPILE_DEFINITIONS ${MT_PORT_DEFINES_UserInterface})
+endif()
diff --git a/extension/src/platform/EterBase/Debug.cpp b/extension/src/platform/EterBase/Debug.cpp
index 802514ae..6e666225 100644
--- a/extension/src/platform/EterBase/Debug.cpp
+++ b/extension/src/platform/EterBase/Debug.cpp
@@ -6,10 +6,12 @@
 
 #include "../PlatformStub.h"
 #include "EterBase/Timer.h"
+#include "LogBox.h"
 
 #include <cstdarg>
 #include <cstdio>
 #include <ctime>
+#include <string>
 
 const DWORD DEBUG_STRING_MAX_LEN = 1024;
 
@@ -97,14 +99,52 @@ auto TraceErrorWithoutEnter(const char *, ...) -> void
 	MT_PLATFORM_STUB();
 }
 
-auto LogBox(const char *, const char *, HWND) -> void
+namespace
 {
-	MT_PLATFORM_STUB();
+std::string& log_box_message()
+{
+	static std::string message;
+	return message;
+}
 }
 
-auto LogBoxf(const char *, ...) -> void
+const std::string& LastLogBoxMessage()
 {
-	MT_PLATFORM_STUB();
+	return log_box_message();
+}
+
+void ClearLogBoxMessage()
+{
+	log_box_message().clear();
+}
+
+void LogBox(const char * c_szMsg, const char * c_szCaption, HWND)
+{
+	// 40250 pops a MessageBox on g_PopupHwnd and Tracen()s the text. There is no window here and no
+	// log file yet, so stderr is the whole of it; the text is also kept for the caller (LogBox.h),
+	// because it is the only place a script traceback survives.
+	std::string& message = log_box_message();
+	message = c_szCaption ? c_szCaption : "LOG";
+	message += ": ";
+	message += c_szMsg ? c_szMsg : "";
+
+	fprintf(stderr, "%s\n", message.c_str());
+	fflush(stderr);
+	Tracen(c_szMsg);
+}
+
+void LogBoxf(const char * c_szFormat, ...)
+{
+	va_list args;
+	va_start(args, c_szFormat);
+
+	char szBuf[2048];
+	_vsnprintf(szBuf, sizeof(szBuf), c_szFormat, args);
+	va_end(args); // PORT: 40250 leaks the va_list; on this ABI va_end is not optional
+
+	// PORT: _vsnprintf does not terminate on truncation.
+	szBuf[sizeof(szBuf) - 1] = '\0';
+	LogBox(szBuf);
 }
 
 auto LogFile(const char *) -> void
diff --git a/extension/src/platform/EterBase/LogBox.h b/extension/src/platform/EterBase/LogBox.h
new file mode 100644
index 00000000..d94591ec
--- /dev/null
+++ b/extension/src/platform/EterBase/LogBox.h
@@ -0,0 +1,14 @@
+#pragma once
+// The text 40250 would have put in a message box (EterBase/Debug.cpp LogBox/LogBoxf).
+//
+// LogBox is the client's fatal-error channel: Traceback() in ScriptLib/PythonLauncher.cpp reports every
+// failed script line through it, and RunMainScript's callers show it and quit. There is no message box
+// on this platform, so the implementation writes the text to stderr and keeps it here for whoever asked
+// for the work — that is how a caller learns *why* a script failed, since Traceback() fetches the
+// exception (and so clears it) before returning.
+
+#include <string>
+
+// The last LogBox/LogBoxf text, "" when none since the last ClearLogBoxMessage().
+const std::string& LastLogBoxMessage();
+void ClearLogBoxMessage();
diff --git a/extension/src/platform/ScriptLib/PythonBoot.cpp b/extension/src/platform/ScriptLib/PythonBoot.cpp
new file mode 100644
index 00000000..7e4962a0
--- /dev/null
+++ b/extension/src/platform/ScriptLib/PythonBoot.cpp
@@ -0,0 +1,150 @@
+// See PythonBoot.h. The sequence is 40250 UserInterface.cpp:241-352 (RunMainScript) and 419-434 (Main),
+// split so the launcher can outlive the call that creates it.
+#include "ScriptLib/StdAfx.h"
+#include "ScriptLib/PythonLauncher.h"
+#include "UserInterface/StdAfx.h" // initpack and the rest of the module initializer list
+#include "PythonBoot.h"
+#include "PythonHost.h"
+#include "../EterBase/LogBox.h"
+
+#include <memory>
+
+namespace
+{
+// 40250 has this on Main()'s stack. CPythonLauncher is a CSingleton, so there is still only ever one.
+std::unique_ptr<CPythonLauncher> g_launcher;
+
+bool fail(std::string* error, const std::string& text)
+{
+	if (error)
+		*error = text;
+	return false;
+}
+}
+
+namespace PythonBoot
+{
+
+bool IsRunning()
+{
+	return g_launcher != nullptr;
+}
+
+bool Start(const char* stdlib_path, std::string* error)
+{
+	if (g_launcher)
+		return true;
+
+	const std::string stdlib = (stdlib_path && *stdlib_path) ? stdlib_path : PythonHost::DefaultStdLibPath();
+	if (stdlib.empty())
+		return fail(error, "no Python standard library path (Metin2Python.stdlib_path / $MT_PYTHON_STDLIB)");
+
+	// The flags have to be set before the interpreter starts, i.e. before the constructor below.
+	PythonHost::Configure();
+
+	g_launcher = std::make_unique<CPythonLauncher>(); // Py_Initialize
+	if (!g_launcher->Create())
+	{
+		Stop();
+		return fail(error, "CPythonLauncher::Create failed");
+	}
+
+	std::string stdlib_error;
+	if (!PythonHost::InstallStdLib(stdlib.c_str(), &stdlib_error))
+	{
+		Stop();
+		return fail(error, "InstallStdLib(" + stdlib + "): " + stdlib_error);
+	}
+	return true;
+}
+
+// 40250: RunMainScript
+bool RunMainScript(const char* lpCmdLine, std::string* error)
+{
+	if (!g_launcher)
+		return fail(error, "PythonBoot::Start has not run");
+
+	CPythonLauncher& pyLauncher = *g_launcher;
+
+	// The module initializers, in 40250's order. Everything after initpack (initdbg, initime, initgrp,
+	// initgrpImage, initgrpText, initwndMgr, initudp, initapp, ... initServerStateChecker) is a 2V slice:
+	// system.py stops at the first import of one of them, today `app`.
+	initpack();
+
+	ClearLogBoxMessage();
+
+	NANOBEGIN
+
+	// RegisterDebugFlag
+	{
+		std::string stRegisterDebugFlag;
+
+#ifdef _DISTRIBUTE
+		stRegisterDebugFlag ="__DEBUG__ = 0";
+#else
+		stRegisterDebugFlag ="__DEBUG__ = 1";
+#endif
+
+		if (!pyLauncher.RunLine(stRegisterDebugFlag.c_str()))
+		{
+			TraceError("RegisterDebugFlag Error");
+			return fail(error, "RegisterDebugFlag Error: " + LastLogBoxMessage());
+		}
+	}
+
+	// RegisterCommandLine.
+	// PORT: the "-cs"/"-ncs" auto-login argument is passed through unchanged. Decoding it needs
+	// EterBase/Utils.cpp SplitLine and EterLib/Util.cpp base64_decode, which are declared but not ported
+	// yet; they belong to the login track (批次 2V1) and nothing in this host passes -cs today.
+	{
+		std::string stRegisterCmdLine;
+
+		std::string stCmdLine = lpCmdLine ? lpCmdLine : "";
+
+		stRegisterCmdLine ="__COMMAND_LINE__ = ";
+		stRegisterCmdLine+='"';
+		stRegisterCmdLine+=stCmdLine;
+		stRegisterCmdLine+='"';
+
+		const CHAR* c_szRegisterCmdLine=stRegisterCmdLine.c_str();
+		if (!pyLauncher.RunLine(c_szRegisterCmdLine))
+		{
+			TraceError("RegisterCommandLine Error");
+			return fail(error, "RegisterCommandLine Error: " + LastLogBoxMessage());
+		}
+	}
+	// PORT: 40250 also honours "--pause-before-create-window" here with system("pause") and the XTrap
+	// init check. Neither exists on this platform (no console to pause, no XTrap), so only the RunFile
+	// is kept.
+	{
+		if (!pyLauncher.RunFile("system.py"))
+		{
+			TraceError("RunMain Error");
+			return fail(error, "RunMain Error: " + LastLogBoxMessage());
+		}
+	}
+
+	NANOEND
+	return true;
+}
+
+bool RunLine(const char* source, std::string* error)
+{
+	if (!g_launcher)
+		return fail(error, "PythonBoot::Start has not run");
+
+	ClearLogBoxMessage();
+	if (!g_launcher->RunLine(source ? source : ""))
+		return fail(error, LastLogBoxMessage());
+	return true;
+}
+
+void Stop()
+{
+	if (!g_launcher)
+		return;
+	g_launcher->Clear(); // Main() calls Clear() explicitly before the launcher leaves scope
+	g_launcher.reset();
+}
+
+}
diff --git a/extension/src/platform/ScriptLib/PythonBoot.h b/extension/src/platform/ScriptLib/PythonBoot.h
new file mode 100644
index 00000000..9e8405ab
--- /dev/null
+++ b/extension/src/platform/ScriptLib/PythonBoot.h
@@ -0,0 +1,41 @@
+#pragma once
+// Starting the script layer inside a host process (docs/PORT-PLAN.md 批次 2P step 4).
+//
+// 40250 runs the interpreter on Main()'s stack (UserInterface/UserInterface.cpp:419-434): construct
+// CPythonLauncher, Create(), RunMainScript(), Clear(), all inside one WinMain. Godot owns the process
+// here and calls in from GDScript, so the launcher has to outlive the call that starts it — that split
+// (Start / RunMainScript / Stop) is the only difference from the original control flow.
+//
+// It lives under platform/ScriptLib rather than platform/UserInterface because it is only buildable
+// with the embedded interpreter, and that is the directory both port_logic and port_platform drop when
+// `mtpython` is absent (extension/src/port/CMakeLists.txt).
+//
+// godot-free, like everything else under platform/: extension/src/python_host_node.cpp is what GDScript
+// talks to.
+
+#include <string>
+
+namespace PythonBoot
+{
+// PythonHost::Configure() -> CPythonLauncher -> Create() -> PythonHost::InstallStdLib(stdlib_path).
+// An empty stdlib_path means PythonHost::DefaultStdLibPath(). Starting twice is a no-op that succeeds.
+// On failure *error is set and the interpreter is shut down again, so the next attempt starts clean.
+// The packs must already be registered (platform/PackBackend.h), as 40250 registers them in Main()
+// before the launcher exists.
+bool Start(const char* stdlib_path, std::string* error);
+bool IsRunning();
+
+// 40250: RunMainScript(CPythonLauncher&, const char*) — the module initializers, __DEBUG__,
+// __COMMAND_LINE__ and RunFile("system.py"). Only the initializers that are ported are called; the rest
+// arrive with the 2V slices, which is why system.py still stops at its first import.
+// False leaves *error set to what the launcher reported through LogBox (platform/EterBase/LogBox.h).
+bool RunMainScript(const char* lpCmdLine, std::string* error);
+
+// CPythonLauncher::RunLine, with the reported text handed back rather than only shown. The host's own
+// check uses it to prove the interpreter and the standard library work in-process on a device that has
+// no 40250 packs, which is where RunMainScript cannot run at all.
+bool RunLine(const char* source, std::string* error);
+
+// 40250 Main() calls Clear() and lets the launcher leave scope.
+void Stop();
+}
diff --git a/extension/src/python_host_node.cpp b/extension/src/python_host_node.cpp
new file mode 100644
index 00000000..e03b2025
--- /dev/null
+++ b/extension/src/python_host_node.cpp
@@ -0,0 +1,94 @@
+#include "python_host_node.h"
+
+#include <godot_cpp/core/class_db.hpp>
+
+#include "python_stdlib.h"
+
+#ifdef MTGODOT_HAVE_PYTHON
+// Standard types only — PythonBoot.h keeps <Python-2.7/*> and the Win32 shims out of this translation
+// unit, which has to stay compilable next to godot-cpp.
+#include "platform/ScriptLib/PythonBoot.h"
+#include <string>
+#endif
+
+using namespace godot;
+
+namespace mtgodot {
+
+#ifdef MTGODOT_HAVE_PYTHON
+
+String Metin2PythonHost::start(const String &stdlib_path) {
+	String path = stdlib_path;
+	if (path.is_empty()) {
+		path = Metin2Python::stdlib_path(false);
+		if (path.is_empty()) {
+			return String("python27.zip unavailable: ") + Metin2Python::last_error();
+		}
+	}
+	std::string error;
+	if (!PythonBoot::Start(path.utf8().get_data(), &error)) {
+		return String::utf8(error.c_str());
+	}
+	return String();
+}
+
+bool Metin2PythonHost::is_running() {
+	return PythonBoot::IsRunning();
+}
+
+String Metin2PythonHost::run_main_script(const String &command_line) {
+	std::string error;
+	if (!PythonBoot::RunMainScript(command_line.utf8().get_data(), &error)) {
+		return String::utf8(error.c_str());
+	}
+	return String();
+}
+
+String Metin2PythonHost::run_line(const String &source) {
+	std::string error;
+	if (!PythonBoot::RunLine(source.utf8().get_data(), &error)) {
+		return String::utf8(error.c_str());
+	}
+	return String();
+}
+
+void Metin2PythonHost::stop() {
+	PythonBoot::Stop();
+}
+
+#else
+
+// Built without -DMTGODOT_EMBED_PYTHON=ON: the class is still registered so GDScript can tell "no
+// interpreter in this build" apart from "the interpreter failed to start".
+String Metin2PythonHost::start(const String &) {
+	return String("this build has no embedded Python (-DMTGODOT_EMBED_PYTHON=ON)");
+}
+
+bool Metin2PythonHost::is_running() {
+	return false;
+}
+
+String Metin2PythonHost::run_main_script(const String &) {
+	return String("this build has no embedded Python (-DMTGODOT_EMBED_PYTHON=ON)");
+}
+
+String Metin2PythonHost::run_line(const String &) {
+	return String("this build has no embedded Python (-DMTGODOT_EMBED_PYTHON=ON)");
+}
+
+void Metin2PythonHost::stop() {
+}
+
+#endif
+
+void Metin2PythonHost::_bind_methods() {
+	ClassDB::bind_static_method("Metin2PythonHost", D_METHOD("start", "stdlib_path"),
+							   &Metin2PythonHost::start, DEFVAL(String()));
+	ClassDB::bind_static_method("Metin2PythonHost", D_METHOD("is_running"), &Metin2PythonHost::is_running);
+	ClassDB::bind_static_method("Metin2PythonHost", D_METHOD("run_main_script", "command_line"),
+							   &Metin2PythonHost::run_main_script, DEFVAL(String()));
+	ClassDB::bind_static_method("Metin2PythonHost", D_METHOD("run_line", "source"), &Metin2PythonHost::run_line);
+	ClassDB::bind_static_method("Metin2PythonHost", D_METHOD("stop"), &Metin2PythonHost::stop);
+}
+
+} // namespace mtgodot
diff --git a/extension/src/python_host_node.h b/extension/src/python_host_node.h
new file mode 100644
index 00000000..4b5f9f79
--- /dev/null
+++ b/extension/src/python_host_node.h
@@ -0,0 +1,38 @@
+#pragma once
+// Metin2PythonHost — the 40250 script layer inside the Godot process (docs/PORT-PLAN.md 批次 2P step 4).
+//
+//   Metin2Pack.initialize(AssetRoot.client_path())   # the packs system.py is read from
+//   if Metin2PythonHost.start() == "":
+//       var err := Metin2PythonHost.run_main_script("")
+//
+// Both calls answer with "" on success and with the reason otherwise, so GDScript never has to guess
+// from a bool. Until 批次 2V0 registers the C++ modules, run_main_script() is expected to come back with
+// system.py's first import error; that is what step 4 verifies on each target platform.
+//
+// This is the only unit that knows both godot-cpp and the port tree: the sequence itself lives in
+// platform/ScriptLib/PythonBoot.h, which stays godot-free.
+
+#include <godot_cpp/classes/object.hpp>
+#include <godot_cpp/variant/string.hpp>
+
+namespace mtgodot {
+
+class Metin2PythonHost : public godot::Object {
+	GDCLASS(Metin2PythonHost, godot::Object)
+
+public:
+	// Stages the standard library (Metin2Python::stdlib_path) when `stdlib_path` is empty, then starts
+	// the interpreter. "" on success, including when it was already running.
+	static godot::String start(const godot::String &stdlib_path);
+	static bool is_running();
+	// __DEBUG__, __COMMAND_LINE__ and system.py out of the packs. "" when system.py ran to the end.
+	static godot::String run_main_script(const godot::String &command_line);
+	// One line of Python in the same __main__ dictionary. "" when it ran.
+	static godot::String run_line(const godot::String &source);
+	static void stop();
+
+protected:
+	static void _bind_methods();
+};
+
+} // namespace mtgodot
diff --git a/extension/src/register_types.cpp b/extension/src/register_types.cpp
index 67264410..4d87e96b 100644
--- a/extension/src/register_types.cpp
+++ b/extension/src/register_types.cpp
@@ -12,6 +12,7 @@
 #include "net/m2_client.h"
 #include "pack40250_node.h"
 #include "proto/proto_node.h"
+#include "python_host_node.h"
 #include "python_stdlib.h"
 #include "static_object.h"
 #include "terrain_splat.h"
@@ -47,6 +48,7 @@ void initialize_mtgodot_module(ModuleInitializationLevel p_level) {
 	GDREGISTER_CLASS(mtgodot::Metin2Proto);
 	GDREGISTER_CLASS(mtgodot::Metin2Pack);
 	GDREGISTER_CLASS(mtgodot::Metin2Python);
+	GDREGISTER_CLASS(mtgodot::Metin2PythonHost);
 }
 
 void uninitialize_mtgodot_module(ModuleInitializationLevel p_level) {
diff --git a/project/client_main.gd b/project/client_main.gd
index 0f649937..6dac593f 100644
--- a/project/client_main.gd
+++ b/project/client_main.gd
@@ -24,6 +24,17 @@ func _ready() -> void:
 		t.name = "PackageRenderTest"
 		add_child(t)
 		return
+	# MT_TEST_MODE=python：在 app 进程里起内嵌解释器跑 system.py（PORT-PLAN 批次 2P step 4）。
+	# 导出模板不接受 --script，这是在真机 APK/IPA 里跑这条检查的唯一入口。
+	if OS.get_environment("MT_TEST_MODE") == "python":
+		AssetPack.ensure()
+		var fail: int = preload("res://python_host_check.gd").new().run()
+		if fail == 0:
+			print("PASS: python_host_check (app 进程内 system.py)")
+		else:
+			printerr("%d check(s) failed" % fail)
+		get_tree().quit(1 if fail else 0)
+		return
 	if OS.get_environment("MT_TEST_MODE") == "forest_render":
 		var forest := ForestMapRenderTest.new()
 		forest.name = "ForestMapRenderTest"
diff --git a/project/python_host_check.gd b/project/python_host_check.gd
new file mode 100644
index 00000000..86791a32
--- /dev/null
+++ b/project/python_host_check.gd
@@ -0,0 +1,60 @@
+# python_host_check —— 在 app 进程里把内嵌解释器起来并跑 system.py（docs/PORT-PLAN.md 批次 2P step 4）。
+#
+# 和 ctest 的 `port.python_launcher` 跑的是同一条序列，区别只有一个：那边是独立可执行文件，这边在
+# Godot 进程里，由 GDScript 发起 —— step 4 要验的就是这个差别。2V0 把 C++ 模块注册上之前，
+# system.py 停在第一个 import（`No module named app`），这就是当前的验收结果。
+#
+# 真机上通常没有 40250 的 Client/pack（APK 里只有 python27.zip），所以分两段：解释器 + 标准库这一段
+# 不需要 pack，任何平台都跑；system.py 这一段需要 pack，没有就跳过并说清楚。
+#
+# 桌面：python_host_test.gd（--script）；真机：MT_TEST_MODE=python 从 client_main.gd 进来。
+extends RefCounted
+
+# 2V0 之前 system.py 必然停在这里；2V0 之后这一行要跟着改。
+const EXPECTED_STOP := "No module named app"
+
+var fail := 0
+
+func _ck(ok: bool, message: String) -> void:
+	if not ok:
+		fail += 1
+		printerr("FAIL: " + message)
+	else:
+		print("ok: " + message)
+
+# 返回失败数；0 表示落在预期的停止点上（或按上面的规则跳过）。
+func run() -> int:
+	if not ClassDB.class_exists("Metin2PythonHost"):
+		printerr("FAIL: Metin2PythonHost extension is not registered")
+		return 1
+	if not FileAccess.file_exists("res://python27.zip"):
+		print("SKIP: python_host_check（没有 res://python27.zip，需要 -DMTGODOT_EMBED_PYTHON=ON 的构建）")
+		return 0
+
+	# 40250 Main() 先注册 pack，再造 CPythonLauncher —— system.py 是从 pack 里读出来的。
+	var has_pack := AssetRoot.pack_ready()
+
+	var start_error: String = Metin2PythonHost.start("")
+	_ck(start_error == "", "解释器在 app 进程里起来了：" + start_error)
+	if start_error != "":
+		return fail
+	_ck(Metin2PythonHost.is_running(), "is_running() 为真")
+	_ck(Metin2PythonHost.start("") == "", "重复 start() 是空操作")
+
+	# 标准库真的在 sys.path 上（真机是沙盒里那份 python27.zip），codec 注册表也重建过。
+	_ck(Metin2PythonHost.run_line("import os, string, types, codecs") == "", "标准库可 import")
+	_ck(Metin2PythonHost.run_line("assert u'\\xe4'.encode('cp1252') == '\\xe4'") == "", "codec 注册表可用")
+	_ck(Metin2PythonHost.run_line("import sys; assert sys.path") == "", "sys.path 非空")
+
+	if has_pack:
+		# RunMainScript：initpack() + __DEBUG__ + __COMMAND_LINE__ + RunFile("system.py")。
+		var err: String = Metin2PythonHost.run_main_script("")
+		print("system.py -> %s" % err)
+		_ck(err.contains(EXPECTED_STOP),
+				"system.py 停在预期的 '%s'（2V0 之后这里会往前走）" % EXPECTED_STOP)
+	else:
+		print("SKIP: system.py 这一段（没有 40250 Client/pack：%s）" % AssetRoot.client_path())
+
+	Metin2PythonHost.stop()
+	_ck(not Metin2PythonHost.is_running(), "stop() 之后 is_running() 为假")
+	return fail
diff --git a/project/python_host_test.gd b/project/python_host_test.gd
new file mode 100644
index 00000000..4ac78222
--- /dev/null
+++ b/project/python_host_test.gd
@@ -0,0 +1,15 @@
+# python_host_test —— 桌面上跑 python_host_check（docs/PORT-PLAN.md 批次 2P step 4）。
+#   godot --headless --path project --script python_host_test.gd
+# 真机上同一份检查从 client_main.gd 的 MT_TEST_MODE=python 进来。
+extends SceneTree
+
+const PythonHostCheck = preload("res://python_host_check.gd")
+
+func _init() -> void:
+	var fail: int = PythonHostCheck.new().run()
+	if fail == 0:
+		print("PASS: python_host_test (app 进程内 system.py)")
+		quit(0)
+	else:
+		printerr("%d check(s) failed" % fail)
+		quit(1)