Fix macOS native CEF bundle layout in PrepareJustCefNative

[jensrot]

Problem

On macOS, a completely clean checkout can never run: dotnet build/dotnet run on a consuming app (e.g. Grayjay.Desktop.CEF) fails at startup with:

Unhandled exception occurred: System.Exception: Failed to find justcefnative
   at JustCef.JustCefProcess.Start(String args)

The PrepareJustCefNative MSBuild target in JustCef.csproj downloads the platform-specific CEF archive and copies its contents into <output>/cef/..., preserving the archive's internal structure. That's correct for Linux/Windows, where the archive is a flat binary and cef/<binary> is exactly where JustCefProcess.GenerateSearchPaths() looks.

On macOS, though, the archive is a full .app bundle (Contents/MacOS/, Contents/Frameworks/, Contents/Resources/). Copying that into a folder named cef/ produces cef/Contents/MacOS/justcefnative — but GenerateSearchPaths() only ever checks for justcefnative.app/Contents/MacOS/... or JustCef.app/Contents/MacOS/.... It never checks cef/. So the binary is never found.

It's not just a search-path bug

I first tried the "obvious" fix — teaching GenerateSearchPaths() to also check cef/Contents/MacOS/{binary}. That does let JustCefProcess find and launch the binary, but CEF/Chromium then immediately fails on its own:

[ERROR:base/i18n/icu_util.cc:177] icudtl.dat not found in bundle
[ERROR:base/i18n/icu_util.cc:232] Invalid file descriptor to ICU data received.

...and the child process silently exits. CEF resolves bundle-relative resources (icudtl.dat under Contents/Frameworks/*.framework/Resources, and presumably others) against the real containing directory, which has to actually be named *.app for its own internal bundle-resolution logic to work — a plain cef/ directory with the identical internal layout isn't enough, even once the executable itself is locatable.

Fix

Change PrepareJustCefNative's output folder name based on RID: justcefnative.app/ on macOS (osx-*), unchanged cef/ everywhere else. This means the bundle root is named correctly for both problems at once — GenerateSearchPaths()'s existing (unmodified) justcefnative.app/Contents/MacOS/... check now matches, and CEF's own resource resolution works because the directory really is *.app. No C# changes needed at all.

+    <JustCefOutputSubdir Condition="$(JustCefRid.StartsWith('osx-'))">justcefnative.app</JustCefOutputSubdir>
+    <JustCefOutputSubdir Condition="'$(JustCefOutputSubdir)' == ''">cef</JustCefOutputSubdir>
...
-        <TargetPath>cef/%(_JustCefFiles.RecursiveDir)%(_JustCefFiles.Filename)%(_JustCefFiles.Extension)</TargetPath>
+        <TargetPath>$(JustCefOutputSubdir)/%(_JustCefFiles.RecursiveDir)%(_JustCefFiles.Filename)%(_JustCefFiles.Extension)</TargetPath>

How to reproduce (before this fix)

On a clean macOS checkout of Grayjay.Desktop (which consumes this repo as a submodule):

git clone <Grayjay.Desktop repo>
cd Grayjay.Desktop
git submodule update --init --recursive
cd Grayjay.Desktop.CEF
dotnet run

Result: System.Exception: Failed to find justcefnative, every time, on a first build. Inspecting the output directory shows the bundle sitting at bin/Debug/net8.0/osx-arm64/cef/Contents/MacOS/justcefnative — never a path GenerateSearchPaths() actually checks.

How I verified the fix

1. Applied this same change directly against the exact JustCef commit pinned by Grayjay.Desktop's submodule.
2. Removed all bin/obj output for a fully clean rebuild — no manual workarounds, no pre-existing justcefnative.app folder.
3. dotnet build + dotnet run in Grayjay.Desktop.CEF: output now correctly lands at bin/Debug/net8.0/osx-arm64/justcefnative.app/Contents/MacOS/justcefnative.
4. App launches cleanly end-to-end: native window opens and gets focus, backend initializes (database, plugins), no icudtl.dat error, no missing-binary error.
5. Confirmed Linux/Windows behavior is untouched — JustCefRid.StartsWith('osx-') is false for every other RID, so JustCefOutputSubdir still resolves to cef exactly as before.

Scope

Single file, JustCef.csproj, +13/-1 lines. No C# changes. No behavior change for non-macOS RIDs.