SteamOS NVIDIA Installer 0.2.0

This release delivers the Gamescope build that fixes corrupted Game Mode menus on
NVIDIA. Nothing else changes: every other file in it is byte identical to 0.1.9.

Install 0.1.9 first if you are still on 0.1.8 or older. An installed version writes
only the files it was built knowing about, and Gamescope was added to that list in
0.1.9. Going straight from 0.1.8 to this release would install the tools and skip the
Gamescope binary, and the machine would then report itself up to date without the fix.
0.1.9 says plainly which files it is leaving for a later release, so it is easy to
tell. A system installed from a 0.1.9 image or newer is unaffected.

What the fix does

With a menu open over a game, Gamescope could hand the game and Steam's interface
straight to two hardware planes and let the display engine blend them. On NVIDIA that
blend draws displaced and repeated fragments of the interface, black rectangles,
coloured bands and speckle over much of the screen, while the upper part of the menu
stays readable.

This build refuses that route when a layer that needs alpha blending would be placed on
a plane, on a display device the kernel reports as nvidia-drm. The frame is composited
instead, which is what already happens whenever the overlay is on, HDR is on, or the
image scale is not one to one. Those three settings were the only known workarounds and
they are no longer needed.

GAMESCOPE_NVIDIA_COMPOSITE_ALPHA=0 in the Gamescope session opts out of this one
reason. Every other reason to composite still applies, so opting out does not mean
direct presentation is guaranteed.

What was measured

On one PC with an RTX 5060, over DisplayPort and HDMI, at 2560x1440 in 165, 144, 120 and
60 Hz and at 1920x1080 in 120 and 60 Hz, with HDR off and on, with VRR off and on where
the connection offered it, and with the performance overlay off and on. The menus were
checked in the main Steam interface, over a running game, during a controller
notification and through repeated rapid opening and closing.

Every result was attributed from Gamescope's own record of which route it chose, not
from appearance alone, and the corruption was deliberately reproduced with the change
disabled on both connections, so a clean picture is not simply a machine that stopped
failing on its own.

Two things that were expected and turned out false, recorded because they were in this
project's own documentation: a lower output resolution is not a workaround and was worse
here, and HDMI is not a separate fault but the same one reached more often, because that
display offers more small modes over HDMI.

What is not established

The precise defect inside the closed driver is not identified. This avoids a
presentation route rather than repairing it, and it does not separate the blend itself
from plane programming, buffer layout or synchronisation. It is not evidence that every
similar report elsewhere has the same cause.

No performance claim is made. Power was sampled with the presentation route changed, but
the scene was a game with moving opponents rather than a repeatable benchmark, so the
difference cannot be attributed to the route.

Validation: the source tree passed its test suite, 272 tests. The bundle is byte
identical to the one published as 0.1.9, so the only thing that changed is which version
the manifest declares and therefore which files an installed tool will now place.