Title: Cyberpunk 2077 (1091500) crashes at startup after latest patch: SIGILL in libnvidia-gpucomp during vkCreateComputePipelines (RTX 2080, 615.71.09)

Summary
After installing the latest Cyberpunk 2077 patch (new content update), the game no longer starts. The launcher works and Cyberpunk2077.exe loads, but ~5 seconds into the game process it crashes while compiling shaders. The same setup worked before the patch.

System

• GPU: NVIDIA GeForce RTX 2080
• Driver: NVIDIA 615.71.09 (proprietary)
• OS: Ubuntu 25.x
• Kernel: 7.0.0-38-generic
• Steam: snap package
• Proton: Experimental 11.0-20261014 (steamrt4 4.0.20261021.265997)
• DXVK: v3.1.1-97-ga78a467cadb22be
• vkd3d-proton: 3.1.0, build 0bb64c56c8f0dcc
• Game: Cyberpunk 2077, Steam App ID 1091500, Build ID 26161058
• CPU: Intel(R) Core(TM) i7-8086K

What happens
The vkd3d-proton device is created successfully (DXR 1.2 and DX Ultimate reported, SM 6.8 enabled, NVAPI/DLSS modules load fine). Then, a few seconds later, the log shows this immediately before the crash:

Unsupported:   %.i0134.cast.i0 = extractelement <8 x i4> %.i0134.cast, i64 0
warn:seh:handle_syscall_fault backtrace: --- Exception 0xc000001d at 0x799a7119b07e: /usr/lib/pressure-vessel/overrides/lib/x86_64-linux-gnu/libnvidia-gpucomp.so.615.71.09 + 0x39b07e
err:vulkan:vkCreateComputePipelines Exception 0xc000001d in Unix call.

The game process exits right after (no further vkd3d-proton errors).

My reading (not confirmed)
The DXIL translator seems to hit an unsupported <8 x i4> vector construct in a compute shader added by the patch, and the resulting pipeline then triggers an illegal-instruction fault inside the NVIDIA driver's shader compiler. I can't tell from the log whether the bug is in the translation, in the driver, or both, so I'm reporting it here and on the NVIDIA Linux forum.

Steps to reproduce

1. Update Cyberpunk 2077 to the latest patch.
2. Launch via Proton Experimental.
3. The game exits during the first shader compilation, before any window shows content.

Already tried
cleared shadercache for 1091500, different driver, different Proton

steam-1091500.log

Attachments
Full Proton log (PROTON_LOG=1): steam-1091500.log [attach]

Happy to run with extra debug env vars (VKD3D_DEBUG, VKD3D_SHADER_DEBUG, etc.) or capture a shader dump if that helps.