feat(linux/portal): improve XDG portal capture for KDE and dual GPU systems

[Traine9]

Summary

• Add KDE popup screen capture support with ScreenCast-only fallback
• Add restore_token support for session persistence
• Handle dual GPU (Intel + NVIDIA) systems: use memory buffers for CUDA when display is on Intel, enable DMA-BUF when display is on NVIDIA
• Add "XDG Portal" option to web UI capture dropdown
• Add build instructions for XDG Portal support in README

Test plan

• Test on KDE Plasma 6 Wayland
• Test on hybrid GPU system (Intel + NVIDIA)
• Test on pure NVIDIA system
• Verify web UI shows portal capture option

[parkerlreed]

GCC 15.2.1 has some warnings around the portal grab

[ 96%] Building CXX object CMakeFiles/sunshine.dir/src/platform/linux/input/inputtino_pen.cpp.o
[ 96%] Building CXX object CMakeFiles/sunshine.dir/src/platform/linux/input/inputtino_touch.cpp.o
[ 96%] Building CXX object CMakeFiles/sunshine.dir/src/platform/linux/publish.cpp.o
/home/parker/build/Sunshine/src/platform/linux/portalgrab.cpp:638:123: error: invalid use of incomplete type ‘class portal::session_cache_t’
  638 |     inline static const std::unique_ptr<session_cache_t> instance_ = std::unique_ptr<session_cache_t>(new session_cache_t());
      |                                                                                                                           ^
/home/parker/build/Sunshine/src/platform/linux/portalgrab.cpp:554:9: note: definition of ‘class portal::session_cache_t’ is not complete until the closing brace
  554 |   class session_cache_t {
      |         ^~~~~~~~~~~~~~~
[ 97%] Building CXX object CMakeFiles/sunshine.dir/src/platform/linux/graphics.cpp.o
In file included from /usr/include/c++/15/memory:80,
                 from /home/parker/build/Sunshine/src/platform/linux/portalgrab.cpp:9:
/usr/include/c++/15/bits/unique_ptr.h: In instantiation of ‘constexpr void std::default_delete<_Tp>::operator()(_Tp*) const [with _Tp = portal::session_cache_t]’:
/usr/include/c++/15/bits/unique_ptr.h:398:17:   required from ‘constexpr std::unique_ptr<_Tp, _Dp>::~unique_ptr() [with _Tp = portal::session_cache_t; _Dp = std::default_delete<portal::session_cache_t>]’
  398 |           get_deleter()(std::move(__ptr));
      |           ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~
/home/parker/build/Sunshine/src/platform/linux/portalgrab.cpp:638:58:   required from here
  638 |     inline static const std::unique_ptr<session_cache_t> instance_ = std::unique_ptr<session_cache_t>(new session_cache_t());
      |                                                          ^~~~~~~~~
/usr/include/c++/15/bits/unique_ptr.h:92:9: error: ‘portal::session_cache_t::~session_cache_t()’ is private within this context
   92 |         delete __ptr;
      |         ^~~~~~~~~~~~
/home/parker/build/Sunshine/src/platform/linux/portalgrab.cpp:628:5: note: declared private here
  628 |     ~session_cache_t() {
      |     ^
make[2]: *** [CMakeFiles/sunshine.dir/build.make:541: CMakeFiles/sunshine.dir/src/platform/linux/portalgrab.cpp.o] Error 1
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [CMakeFiles/Makefile2:2043: CMakeFiles/sunshine.dir/all] Error 2
make: *** [Makefile:156: all] Error 2

[Traine9]

fixed all things from @ReenigneArcher , gcc 15 warning should be gone too @parkerlreed

[ReenigneArcher]

@Traine9 appologies, but when I rebase the PR branch, it looks like it always causes conflicts in the portalgrab.cpp. Any chance you can resolve the conflicts again. I think you should just be able to ignore the differences and use the code as is in your branch for portalgrab.cpp.

[Traine9]

@ReenigneArcher merged without force push now you should able to merge it

[sonarqubecloud]

Quality Gate failed

Failed conditions
4 New issues
1 Security Hotspot
4 New Code Smells (required ≤ 0)

See analysis details on SonarQube Cloud

Catch issues before they fail your Quality Gate with our IDE extension SonarQube for IDE

[codecov]

Bundle Report

Changes will increase total bundle size by 90 bytes (0.0%) ⬆️. This is within the configured threshold ✅

Detailed changes

Bundle name	Size	Change
sunshine-esm	968.68kB	90 bytes (0.01%) ⬆️

Affected Assets, Files, and Routes:

view changes for bundle: sunshine-esm

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
assets/config-*.js	90 bytes	60.92kB	0.15%

Files in assets/config-*.js:

• ./src_assets/common/assets/web/configs/tabs/Advanced.vue → Total Size: 9.24kB

[parkerlreed]

Multi touch/pen/stylus seems to be completely non functional with this enabled. Trackpad works as expected.