Fix #374: troubleshooting for the NVIDIA shader-cache startup hang

With Shader Cache Size disabled in NVIDIA Control Panel, the driver walks
the whole system drive inside D3D12CreateDevice (traced by the reporter
to NvMemMapStoragex.dll!TotalDiskUsage), before the window's first
frame; Driver Default fixes it (confirmed in #374, PhotoCraft too). The
launch-argument walk found on the way was fixed in #394.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01912WaK6Rmew3wxZuPyX7E8

docs/gpu-pipeline.md

@@ -69,6 +69,16 @@ rendering; `set VK_LOADER_DRIVERS_DISABLE=*igvk64*` (Vulkan loader) hides a spec
 from every program started with it. Help ▸ System Info and `app.gpu` show the adapter and backend in
 use (e.g. `Intel(R) UHD Graphics 630 (Dx12)`).
 
+**Window never appears, "not responding" (Windows, NVIDIA; issue #374).** With *Shader Cache Size*
+set to **Disabled** in NVIDIA Control Panel (Manage 3D settings → Global Settings), NVIDIA's driver
+walks the whole system drive while the window's GPU device is created (`D3D12CreateDevice` →
+`nvwgf2umx.dll` → `NvMemMapStoragex.dll!TotalDiskUsage`), before the first frame: a black,
+unresponsive window for minutes. The Vulkan driver shares that code, so another backend doesn't
+help. Set *Shader Cache Size* back to **Driver Default** (or any size); the setting is global, there
+is no per-program override. Other programs that create a DX12 or Vulkan device at startup hang the
+same way (PhotoCraft does). It is a driver issue: nothing in LightCraft itself
+walks the drive.
+
 ## Where it is used
 - `lightcraft_engine::media::develop` (called by every `RenderJob`): loupe / before / compare views,
   `render_now` (CLI, MCP, control channel renders) and exports render on the GPU when one is