docs: 文档审计——修正失效链接与过期结论

按 docs/ 目录逐篇核对，只改与事实/路径不符的部分，不动尚未验证的计划条目：

- `docs/steps/**` 在早前整理时已迁到 `docs/reference/steps/**`，全仓的旧路径
  引用（PLAN.md / README.md / M0-gr2-reader.md 及 libgr2 的头注释）一并改正。
- CLIENT-GAP.md / CLIENT-GAP-FIX.md / BACKLOG.md / MIDREVIEW.md：把已经落地的
  条目从「待办」改为已完成，删掉与代码现状矛盾的描述。
- ANDROID-TESTING.md / CLIENT-PORT.md / CLIENT-ROADMAP.md / GODOT-POC-PLAN.md /
  SHINSOO-WORLD-RENDERING.md / PARITY-GAP.md：同上，另补当前实际的构建/测试入口。
- THIRD-PARTY.md：补齐实际在用的第三方来源与许可说明。

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SJugvEJwz3FK4hw9ti3SRb

docs/THIRD-PARTY.md

@@ -1,22 +1,25 @@
 # Third-party native dependencies
 
-The GDExtension links three native libraries that are **not** part of Godot or
-godot-cpp. Phase 1 (macOS) pulled them from Homebrew; that stops working the
-moment we cross-compile for the Android NDK or the iOS SDK (BACKLOG F1/F2), so as
-of 2026-08-30 all three are built from source as part of our own CMake build.
+The GDExtension links four native libraries that are **not** part of Godot or
+godot-cpp. Phase 1 (macOS) pulled the first three from Homebrew; that stops
+working the moment we cross-compile for the Android NDK or the iOS SDK (BACKLOG
+F1/F2), so as of 2026-08-30 they are built from source as part of our own CMake
+build. Crypto++ joined later (2026-09-02) with the `MT_PROTOCOL=classic` 40250
+backend and was vendored the same way from the start.
 
 Everything lives under `extension/third_party/` and is wired by
-`extension/third_party/CMakeLists.txt`, which exposes three aliases:
+`extension/third_party/CMakeLists.txt`, which exposes four aliases:
 
-| Alias           | Backing target   | Consumed by            |
-|-----------------|------------------|------------------------|
-| `mt3p::sodium`  | `sodium`         | `mtnet`, `mtpack`, `mtproto` |
-| `mt3p::zstd`    | `libzstd_static` | `mtpack`               |
-| `mt3p::minilzo` | `minilzo`        | `mtproto`              |
+| Alias             | Backing target   | Consumed by                  |
+|-------------------|------------------|------------------------------|
+| `mt3p::sodium`    | `sodium`         | `mtnet`, `mtpack`, `mtproto` |
+| `mt3p::zstd`      | `libzstd_static` | `mtpack`                     |
+| `mt3p::minilzo`   | `minilzo`        | `mtproto`                    |
+| `mt3p::cryptopp`  | `cryptopp`       | `mtnet` (classic backend)    |
 
-No source file changed: `#include <sodium.h>`, `#include <zstd.h>` and
-`#include <lzo/lzo1x.h>` all still resolve (the last via a 1-line shim header,
-see below).
+No source file changed: `#include <sodium.h>`, `#include <zstd.h>`,
+`#include <lzo/lzo1x.h>` and `#include <cryptopp/…>` all still resolve (the LZO
+one via a 1-line shim header, see below).
 
 ## libsodium — via `robinlinden/libsodium-cmake`
 
@@ -60,11 +63,38 @@ see below).
   or commercial use. (item_proto/mob_proto are the only LZO consumers; a
   clean-room LZO1X decompressor is the eventual fix.)
 
+## Crypto++ — vendored source (not a submodule)
+
+* **Files:** `extension/third_party/cryptopp/` (~6.6 MB), copied from the 40250
+  client tree (`ClientVS22/extern/include/cryptopp`), `CRYPTOPP_VERSION 840` =
+  **8.4.0**. The 40250 server links this exact version
+  (`Server/.../extern/cryptopp_8_4_0.tar.gz`), so the version is pinned by
+  wire compatibility, not preference.
+* **Why:** the `MT_PROTOCOL=classic` backend's `_IMPROVED_PACKET_ENCRYPTION_`
+  cipher — DH2 key agreement + hint-selected block ciphers (Twofish default) in
+  CTR mode. Only consumer is `extension/src/net/classic/classic_cipher.{h,cpp}`.
+  The m2dev backend does not use it (that one is libsodium/XChaCha20).
+* **No upstream CMakeLists**, so `cryptopp/CMakeLists.txt` is ours: it globs the
+  library TUs and drops the cryptest / benchmark / adhoc / FIPS-selftest ones
+  (`adhoc`, `bench1..3`, `datatest`, `dlltest`, `fipsalgt`, `fipstest`, `pch`,
+  `regtest1..4`, `test`, `validat0..10`).
+* **ASM disabled everywhere** (`CRYPTOPP_DISABLE_ASM` / `_SSSE3` / `_AESNI`) so
+  one pure-C++ build works on macOS, the Android NDK and the iOS SDK; the classic
+  cipher needs no AES-NI / SHA-ext. Android additionally compiles the NDK's
+  `sources/android/cpufeatures/cpu-features.c` in, because upstream `cpu.cpp`
+  includes `cpu-features.h` unconditionally under `__ANDROID__`.
+* Built with `-w` (upstream is not warning-clean under `-Wall`) and
+  `-fno-strict-aliasing`.
+* **License:** **public domain** — the compilation carries Wei Dai's copyright,
+  but every individual file is placed in the public domain by its authors
+  (`extension/third_party/cryptopp/License.txt`). Ship-safe; unlike miniLZO it
+  imposes no obligation before a public or commercial release.
+
 ## Rebuilding / fetching
 
 `./build.sh` auto-runs `git submodule update --init --recursive` if any of the
-three (godot-cpp, zstd, libsodium-cmake+libsodium) is missing. miniLZO needs no
-fetch.
+three submodules (godot-cpp, zstd, libsodium-cmake+libsodium) is missing.
+miniLZO and Crypto++ are vendored source and need no fetch.
 
 Homebrew `libsodium` / `zstd` / `lzo` are no longer referenced by the build and
 can be uninstalled.