feat(platform): verify and document Steam Runtime / Steam Deck compatibility for Linux + Windows

[e-gleba]

Summary

Add verified CMake presets and CI jobs that target the Steam Runtime (Linux) and produce Windows binaries compatible with Steam distribution requirements. Goal: a game or tool built from this template drops into Steam without runtime library conflicts on Steam Deck, Ubuntu 20.04+ baseline, or Windows 10+.

Motivation

Indie gamedev is the largest segment of solo/small-team C++ developers on Steam. Most CMake templates ignore Steam entirely; developers discover ABI incompatibilities (glibc too new, C++ stdlib mismatch, missing steam-runtime symbols) only after their first upload. A template that pre-verifies Steam Runtime compatibility is a direct differentiator against cpp-best-practices, kigster, and generic starters.

Acceptance Criteria

• Add linux-steam-sniper configure preset that targets Steam Runtime Sniper (Ubuntu 22.04-based scout successor); build inside registry.gitlab.steamos.cloud/steamrt/sniper/sdk container or equivalent
• Verify libc.so.6, libstdc++.so.6, and libgcc_s.so.1 ABI compatibility against Steam Runtime manifest
• Add CI job that runs steam-runtime-check or steamrt/tasks/check-abi on produced binary
• Document Windows preset msvc-steam / llvm-mingw-steam-x86_64 with static CRT linkage (/MT or -static-libgcc -static-libstdc++) to avoid VC++ redist dependency for Steam
• Verify produced .exe has no external dependency on vcruntime140.dll / msvcp140.dll (use dumpbin /dependents or ldd equivalent on Wine)
• Provide steam_appid.txt template, deploy/ directory structure, and CPack generator for .zip ready for SteamPipe
• Test binary execution on Steam Deck (Arch-based SteamOS) via GitHub Actions self-hosted runner or community validation

Research & References

• Steam Runtime on GitHub — ValveSoftware/steam-runtime — official SDK containers, ABI checker, and setup.sh scripts ValveSoftware/steam-runtime
• Steam Runtime Sniper SDK container — GitLab registry with Docker images for CI registry.gitlab.steamos.cloud
• Steamworks SDK Build Instructions — SteamPipe .zip layout, steam_appid.txt, and depot build requirements Steamworks
• Steam Deck Verified Guidelines — fullscreen support, controller glyphs, proton compatibility for non-native binaries Steamworks
• Godot Engine Steam export preset — prior art on containerized Linux builds targeting server/Steam runtime baseline Godot Docs
• itch.io Butler + CMake cross-compilation — indie distribution parallel to Steam; similar static-linking requirements itch.io
• CMake CMAKE_INTERPROCEDURAL_OPTIMIZATION — LTO for smaller Steam binaries cmake.org
• MinGW static linking -static-libgcc -static-libstdc++ — GCC option reference for self-contained Windows executables gcc.gnu.org
• Microsoft VC++ redistributable static linking — /MT vs /MD semantics for Steam-no-redist builds Microsoft Docs