quest: plan a single Vulkan loader and the X11 GPU path on NVIDIA

quest/m0/README.md

@@ -101,6 +101,8 @@ repository.
 - [Web studio](/quest/m0/web.md) - the full studio in wasm on WebGPU and WebCodecs, served from this repository
 - [Virtual camera](/quest/m0/vcam/README.md) - the program or a published scene exposed as a system camera on Linux, Windows, and macOS
 - [Browser sources on the GPU under Mesa](/quest/m0/cef-headless.md) - shared-texture pages paint on Intel and AMD under Wayland, and a page that cannot paint fails loudly
+- [One Vulkan loader for the studio and CEF](/quest/m0/cef-vulkan-loader.md) - NixOS builds and tests find the GPU without VK_DRIVER_FILES
+- [Browser sources on the GPU under X11 on NVIDIA](/quest/m0/cef-x11-nvidia.md) - the X11 GPU path paints on NVIDIA, or falls back to the CPU path loudly
 - [Signing identities are available](/quest/m0/signing.md) - the Apple and Windows code-signing credentials packaging and the macOS camera need
 - [Packaging](/quest/m0/packaging.md) - signed installers for macOS and Windows and a Flatpak for Linux
 - [The persistable portal restore token is pinned](/quest/m0/pin-portal-token.md) - moq-video's restore token, for Wayland sources

quest/m0/cef-vulkan-loader.md

@@ -0,0 +1,25 @@
+# [S] One Vulkan loader for the studio and CEF
+
+## Goal
+
+On NixOS, `cargo run`, `cargo nextest` and an installed studio find the GPU
+through the system Vulkan loader, with no `VK_DRIVER_FILES` or
+`LD_LIBRARY_PATH` set, because the build no longer ships CEF's bundled
+`libvulkan.so.1` beside the binaries.
+
+## Plan
+
+From [moq-dev/studio#59](https://github.com/moq-dev/studio/pull/59), picked
+2026-11-05 (maintainer, /quest-plan), m0 by the rule that fixes join m0.
+
+- ✅ **Stop copying CEF's `libvulkan.so.1`** into the target directory, so
+  the studio and CEF's GPU process both load the system loader. Rejected:
+  exporting `VK_DRIVER_FILES` from the dev shell, which fixes development but
+  not a packaged build.
+- Today the copy in `target/debug` loads first, finds no NixOS drivers, and
+  wgpu gets no adapter. The `render-sw` recipe in the `justfile` works around it
+  by exporting `LD_LIBRARY_PATH` and `VK_DRIVER_FILES`. Drop the workaround if it
+  is no longer needed for the software driver.
+- Verify on NixOS (`ssh nixos`) that CEF's GPU path (Wayland, shared
+  textures) and its SwiftShader CPU path still start, that WebGL still draws,
+  and that the GPU tests find an adapter under plain `cargo nextest`.

quest/m0/cef-x11-nvidia.md

@@ -0,0 +1,26 @@
+# [S] Browser sources on the GPU under X11 on NVIDIA
+
+## Goal
+
+On an NVIDIA GPU in an X11 or XWayland session, browser sources paint on
+the GPU path. If the studio cannot give CEF a GBM device, it detects that at
+startup and takes the CPU path with a note in Health, rather than leaving
+pages stuck in Starting.
+
+## Plan
+
+From [moq-dev/studio#59](https://github.com/moq-dev/studio/pull/59), picked
+2026-11-05 (maintainer, /quest-plan), m0 by the rule that fixes join m0.
+
+- On nixos (RTX 3070 Ti, NVIDIA 580), the GPU path under X11 never paints:
+  CEF's GPU process logs "Can't create buffer -- gbm device is missing".
+  Wayland sessions avoid it since #59, but X11-only sessions still hit it.
+- First find why. Likely suspects: the NVIDIA GBM backend
+  (`nvidia-drm_gbm.so`) is not on CEF's search path (`GBM_BACKENDS_PATH`), or
+  `nvidia-drm` modeset is off. Fix it if the studio can, for example by
+  passing the backend path to the helper or packaging it.
+- Otherwise fail loud: probe for a GBM device when the helper starts, and if
+  there is none, take the CPU path and say why in Health and the Sources panel.
+  Fail on an observed probe result, never on a timeout.
+- Verify on nixos under X11 (XWayland) and record how in the PR; no CI job
+  has a GPU.