NVENC/NVDEC userspace path + nvidia-smi shortcut

- systemd-user environment generator and appsandbox-gpu wrapper both
  append /usr/lib/wsl/lib to LD_LIBRARY_PATH. ldconfig has the .so.1
  entries cached, but the 9P mount is read-only so the unversioned
  symlinks ldconfig wants to create can't be written. dlopen() of
  unversioned names (libcuda.so, libnvidia-encode.so, libnvcuvid.so)
  needs the path on LD_LIBRARY_PATH — without it ffmpeg's h264_nvenc /
  h264_cuvid plugins fail with 'Cannot load libcuda.so.1'.

- setup.sh: symlink /usr/lib/wsl/lib/nvidia-smi to /usr/local/bin so
  the bare command works without env tweaks. Created unconditionally
  because the symlink target is resolved at exec time — the file
  appears under the agent's 9P mount on first boot regardless of when
  the symlink was created.

src/backend_win/disk_util.c

@@ -2762,6 +2762,15 @@ static BOOL generate_ubuntu_setup_sh(const wchar_t *path, BOOL ssh_enabled)
         "fi\n"
         "ldconfig\n"
         "\n"
+        "# --- 7b. nvidia-smi on PATH ---\n"
+        "# WSL/GPU-PV ships nvidia-smi via the host 9P mount at\n"
+        "# /usr/lib/wsl/lib/nvidia-smi (only present when the VM has a\n"
+        "# GPU partition + the agent has mounted the share). The symlink\n"
+        "# is created unconditionally — symlink target is resolved at\n"
+        "# exec time, so it 'comes alive' once the agent mounts the share\n"
+        "# at first boot, with or without the file existing now.\n"
+        "ln -sf /usr/lib/wsl/lib/nvidia-smi /usr/local/bin/nvidia-smi\n"
+        "\n"
         "# --- 8. daemon-reload, enable the helper services, set graphical ---\n"
         "# (Helper binaries + service files are already installed by section 3.\n"
         "#  Clipboard has no system service — agent spawns it as a child.)\n"

tools/linux/wsl-mesa/50-appsandbox-gpu

@@ -19,9 +19,17 @@
 
 WSL_MESA=/opt/wsl-mesa
 WSL_MESA_LIB="$WSL_MESA/lib/x86_64-linux-gnu"
+WSL_LIB=/usr/lib/wsl/lib
 
 if [ -e /dev/dxg ] && [ -d "$WSL_MESA_LIB" ]; then
-    echo "LD_LIBRARY_PATH=$WSL_MESA_LIB"
+    # LD_LIBRARY_PATH covers two needs:
+    #   - $WSL_MESA_LIB picks Mesa's d3d12 gallium + dzn Vulkan over stock.
+    #   - $WSL_LIB lets apps that dlopen the WSL NVIDIA userspace libs by
+    #     unversioned SONAME (libcuda.so, libnvidia-encode.so, libnvcuvid.so)
+    #     find them. ldconfig caches only the .so.1 entries — the 9P mount
+    #     is read-only so the unversioned symlinks can't be created.
+    #     NVENC (h264_nvenc, hevc_nvenc) + NVDEC (h264_cuvid, etc.) need this.
+    echo "LD_LIBRARY_PATH=$WSL_MESA_LIB:$WSL_LIB"
     echo "GALLIUM_DRIVER=d3d12"
     echo "MESA_LOADER_DRIVER_OVERRIDE=d3d12"
     echo "__GLX_VENDOR_LIBRARY_NAME=mesa"

tools/linux/wsl-mesa/appsandbox-gpu

@@ -22,10 +22,17 @@ set -e
 WSL_MESA=/opt/wsl-mesa
 WSL_MESA_LIB="$WSL_MESA/lib/x86_64-linux-gnu"
 WSL_MESA_VK_ICD="$WSL_MESA/share/vulkan/icd.d/dzn_icd.x86_64.json"
+WSL_LIB=/usr/lib/wsl/lib
 
 if [ -e /dev/dxg ] && [ -d "$WSL_MESA_LIB" ]; then
-    # Pick Mesa from /opt/wsl-mesa over stock Ubuntu libGL.
-    export LD_LIBRARY_PATH="$WSL_MESA_LIB${LD_LIBRARY_PATH:+:$LD_LIBRARY_PATH}"
+    # LD_LIBRARY_PATH covers two needs:
+    #   - $WSL_MESA_LIB picks Mesa's d3d12 gallium + dzn Vulkan over stock.
+    #   - $WSL_LIB lets apps that dlopen the WSL NVIDIA userspace libs by
+    #     unversioned SONAME (libcuda.so, libnvidia-encode.so, libnvcuvid.so)
+    #     find them. ldconfig caches only the .so.1 entries — the 9P mount
+    #     is read-only so the unversioned symlinks can't be created.
+    #     NVENC (h264_nvenc, hevc_nvenc) + NVDEC (h264_cuvid, etc.) need this.
+    export LD_LIBRARY_PATH="$WSL_MESA_LIB:$WSL_LIB${LD_LIBRARY_PATH:+:$LD_LIBRARY_PATH}"
     export __GLX_VENDOR_LIBRARY_NAME=mesa
 
     # Both env vars are needed: