Thank you for your answers.
Goal and idea of the project is to have byte-to-byte replay and simulation parity, including visuals - which is fully achieved today for whatever I did tested myself.
I did see several mentions of MSVC in the repository readme, so I was a bit worried there, but it is good that the project can already be compiled with clang.
Everything is kept to original, nothing changed for sim or rendering that changes visual look from the original.
Gotcha. It should be possible to put test assets in the original, take a screen capture, and replay with the test assets in the CI to catch visual bugs, like what emulators do, if you really want to ensure 1:1 fidelity.
If you mean to the repo - I will accept changes that fixes bugs that doesn't affect simulation or any other PRs that fixes things I did missed to repeat original game behavior.
I really meant your repository. There are so many improvements I could think of, more or less user-visible. I listed some, but less-visible improvements could include multi-monitor improvements, steam input integration to make it easier to play on Steam Deck, Discord/Steam rich presence integration, better integration with FAF (integrated lobby, control it via IPC to avoid restarting the game, etc).
Testing Linux build also one of the TODOs, since compiler are clang it's possible but will require x87 math adjustments for the platform.
Yeaaah... I imagine that the game relies on system libraries? Probably not on the windows ucrt "universal c runtime" otherwise we would have seen desyncs on wine, but x87 definitely need some focus. It should be possible to load windows libraries (extracted from MSVC redist) with a small shim (or compiler options) to adjust the calling convention. That would not be my prefered approach though, as it makes it more complicated to support non-x86 platforms (arm) with native code. The other option is to link another controlled FP library, which behaves the same across platforms. This would break replays (the old library can still be embedded to read them on Windows, but new replays would be generated with the new one, unless additional trickery is performed). But you probably thought about all this already.
Something else came to my mind: It should even be possible to compile this to webassembly, and, with a few changes, have a replay player in the browser. The hard part is that assets are copyrighted and distributed with the game, but at least event (commander destruction, experimental unit built, game stats) can be extracted, and maybe a strategic view/minimap provided with custom assets? I am fairly new to FAF (not to supcom, but these decomp projects attracted me to FAF), but I imagine that the community would value that?
