launcher: native DLL bootstrap for single-file under Wine

.NET 8 publish --self-contained -p:PublishSingleFile=true with
-p:IncludeNativeLibrariesForSelfExtract=true bundles the Avalonia /
SkiaSharp native libs inside the bundle and extracts them at startup
to $DOTNET_BUNDLE_EXTRACT_BASE_DIR/<app>/<hash>/ (default
%TEMP%/.net/<app>/<hash>/). On native Windows the CLR adds that path
to the DLL search list automatically, so Avalonia can P/Invoke into
libSkiaSharp.dll without any help.

Under Wine the search path is never updated and P/Invokes from
Avalonia.Skia hit DllNotFoundException for sk_colortype_get_default_8888
before the first frame renders. The launcher crashes in
Avalonia.AppBuilder.SetupUnsafe before any GUI comes up, so the user
just sees "failed to open" style errors with no actionable context.

Fix: the first line of Program.Main locates the extract dir via
DOTNET_BUNDLE_EXTRACT_BASE_DIR env var + app name + a sentinel
(libSkiaSharp.dll) and calls SetDllDirectoryW on it. That puts the
extract dir on the DLL search path for any subsequent LoadLibrary,
which is what Avalonia's P/Invokes end up doing.

Verified under wine-staging 10.15 on Fedora:
- pure single-file .exe in an otherwise empty directory
- no accompanying loose DLLs
- no env var overrides at all
- launcher boots, Avalonia window renders, orchestrator verifies
  manifest 2026.04.15-m2pack-v7 signature, download begins

No-op on native Windows (SetDllDirectoryW is a supported API and the
extract dir is already in the search path, so re-adding it is
harmless). No-op in dev builds where DOTNET_BUNDLE_EXTRACT_BASE_DIR
is unset and the extract dir probe returns null.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

README.md

@@ -34,6 +34,38 @@ dotnet publish src/Metin2Launcher/Metin2Launcher.csproj \
 
 The CI hasn't been wired yet; the MVP only requires the build to succeed.
 
+## Build (Wine bundle)
+
+For Linux users who run the Windows launcher through Wine, the safe layout is
+not a single `Metin2Launcher.exe`. The Wine-compatible launcher currently needs
+the non-single-file `win-x64` publish output, and it must live separately from
+the mutable client install dir so the updater does not patch over its own
+runtime files.
+
+Use:
+
+```
+scripts/build-wine-bundle.sh
+```
+
+This produces:
+
+```
+release-wine/
+  Metin2Launcher-wine/
+    start-launcher.sh
+    README.txt
+    launcher/
+      Metin2Launcher.exe
+      *.dll
+    client/
+  Metin2Launcher-wine.tar.gz
+```
+
+`start-launcher.sh` exports `METIN2_INSTALL_DIR=./client` and then runs
+`wine ./launcher/Metin2Launcher.exe`, so the launcher runtime stays isolated
+from the actual game files.
+
 ## Publishing a release
 
 `scripts/publish-launcher.sh` is the single entry point for cutting a Velopack
@@ -92,6 +124,9 @@ and run it. On first launch it will:
    dev builds)
 5. start `Metin2.exe`
 
+For the Wine bundle layout, do not run the launcher from the mutable client
+directory. Run `./start-launcher.sh` from the bundle root instead.
+
 A log is written to both stdout and `<client>/.updates/launcher.log`. On a plain
 `dotnet run` (no client root yet), the log falls back to
 `%LOCALAPPDATA%/Metin2Launcher/launcher.log` on Windows or

release-wine/Metin2Launcher-wine/README.txt

@@ -0,0 +1,10 @@
+Metin2Launcher Wine bundle
+
+Layout:
+- launcher/  launcher runtime (.exe + DLLs)
+- client/    final game install dir and .updates/ state
+
+Run:
+  ./start-launcher.sh
+
+The launcher installs into client/, not into launcher/.

release-wine/Metin2Launcher-wine/launcher/Metin2Launcher.runtimeconfig.json

@@ -0,0 +1,17 @@
+{
+  "runtimeOptions": {
+    "tfm": "net8.0",
+    "includedFrameworks": [
+      {
+        "name": "Microsoft.NETCore.App",
+        "version": "8.0.22"
+      }
+    ],
+    "configProperties": {
+      "MVVMTOOLKIT_ENABLE_INOTIFYPROPERTYCHANGING_SUPPORT": true,
+      "System.Reflection.Metadata.MetadataUpdater.IsSupported": false,
+      "System.Runtime.InteropServices.BuiltInComInterop.IsSupported": true,
+      "System.Runtime.Serialization.EnableUnsafeBinaryFormatterSerialization": false
+    }
+  }
+}