Metin2 game client (P0–P11) + mobile asset pipeline

Networked client on the existing Godot 4.7 + libgr2 renderer:
- net: m2dev wire protocol (libsodium KX + XChaCha20), auth/select/game
  phases, EntityStore world model, ~all GC/CG headers. char create/delete,
  private shop / mall / cube, SHOP_GC_START_EX, guild, party (+ CG_PARTY_SET_STATE),
  quests, dragon soul, refine, safebox, exchange.
- UI: in-game windows migrated 1:1 from the reference uiscript/root .py —
  char status (/stat), inventory+equipment, select-item ([SELECT_ITEM] quest
  token), system-option + game-option + ESC system menu, private-shop 39-grid,
  party info board, shop tabs, atlas, minimap, quickbar, chat, …
- EterGrnLib polish: GR2 material blend/two-sided, LOD crossfade, motion-event
  dispatch, contact shadow, ray-AABB picking, weapon grip pre-transform.

Portable asset IO (A1) — all extension/libgr2/formats/mtproto reads routed
through godot::FileAccess (res:// PCK works on iOS/Android); standalone-lib
*_path() kept for the non-Godot CTests. AssetResolver + PropertyRegistry
switched to a baked index (bake_asset_index.gd) instead of std::filesystem.

Mobile builds: build-{android,ios}.sh, export-android.sh, pack-assets.sh,
gen-debug-keystore.sh. Assets ship as a zip mounted at runtime by
project/asset_pack.gd (adb push now; HTTP download is a drop-in later).

ctest 10/10, 34 GDScript suites, macOS/iOS/Android all build.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013EJxkHiNKS4kybHS3XKyAJ

extension/src/pack/asset_source.cpp

@@ -0,0 +1,83 @@
+#include "asset_source.h"
+
+#include <cstdio>
+#include <filesystem>
+#include <fstream>
+
+namespace fs = std::filesystem;
+
+namespace mtpack {
+
+bool AssetSource::build(const std::string &assets_root, const std::string &pack_dir,
+		const std::string &cache_dir, std::string *err) {
+	if (!m_loose.build(assets_root, fmt::AssetResolver::default_priority(), err)) {
+		return false;
+	}
+	if (!pack_dir.empty()) {
+		int n = m_packs.scan_dir(pack_dir);
+		m_have_packs = n > 0;
+		m_cache = !cache_dir.empty()
+				? cache_dir
+				: (fs::path(pack_dir) / ".mtcache").string();
+	}
+	return true;
+}
+
+bool AssetSource::exists(const std::string &vpath) const {
+	if (!m_loose.resolve(vpath).empty()) {
+		return true;
+	}
+	return m_have_packs && m_packs.has(vpath);
+}
+
+bool AssetSource::read(const std::string &vpath, std::vector<uint8_t> &out, std::string *err) const {
+	std::string lp = m_loose.resolve(vpath);
+	if (!lp.empty()) {
+		std::ifstream f(lp, std::ios::binary);
+		if (f) {
+			out.assign((std::istreambuf_iterator<char>(f)), std::istreambuf_iterator<char>());
+			return true;
+		}
+	}
+	if (m_have_packs && m_packs.read(vpath, out, err)) {
+		return true;
+	}
+	if (err && err->empty()) {
+		*err = "not found: " + vpath;
+	}
+	return false;
+}
+
+std::string AssetSource::to_path(const std::string &vpath, std::string *err) const {
+	std::string lp = m_loose.resolve(vpath);
+	if (!lp.empty()) {
+		return lp;
+	}
+	if (!m_have_packs || !m_packs.has(vpath)) {
+		if (err) *err = "not found: " + vpath;
+		return "";
+	}
+	// extract to cache/<normalized vpath>, once
+	std::string rel = PackMount::norm(vpath);
+	fs::path dst = fs::path(m_cache) / rel;
+	std::error_code ec;
+	if (fs::exists(dst, ec) && fs::file_size(dst, ec) > 0) {
+		return dst.string();
+	}
+	std::vector<uint8_t> bytes;
+	if (!m_packs.read(vpath, bytes, err)) {
+		return "";
+	}
+	fs::create_directories(dst.parent_path(), ec);
+	std::ofstream o(dst, std::ios::binary | std::ios::trunc);
+	if (!o) {
+		if (err) *err = "cannot write cache file " + dst.string();
+		return "";
+	}
+	o.write(reinterpret_cast<const char *>(bytes.data()),
+			static_cast<std::streamsize>(bytes.size()));
+	o.close();
+	return dst.string();
+}
+
+} // namespace mtpack