Frame Home as the real SteamVR environment on a PC (Windows too), not a home app

On the Steam Frame a layer inside SteamVR's compositor draws the home where it would draw Aurora, so the home is the
environment itself: at boot, during game loads, behind the Steam menu, with the controllers and passthrough, and it
steps aside for a game the instant it opens. On a PC this was faked with SteamVR's home-app slot and a flat 360 photo
in the gaps, which launched and handed off like an app and showed a picture, not the live home. This does it properly
on any PC that runs SteamVR, the Frame's way:

- Windows: the compositor is Direct3D 11, so the layer is a proxy d3d11.dll beside the compositor (layer/
  frame_home_layer_d3d11.cpp, built from the .def that forwards every other export to the real d3d11.dll, kept as
  fh_d3d11real.dll). It wraps the compositor's device, finds Aurora's draws by their shader bytecode and draws the
  home over the sky, leaving the floor and stars off; everything else passes straight through. Pure pass-through in
  any process that isn't vrcompositor.
- The home's frames cross from Frame Home (Vulkan) to the compositor (D3D11): the layer owns kSlots shared textures
  and hands Frame Home their NT handles over a named pipe; Frame Home imports them (VK_KHR_external_memory_win32) and
  renders into them. No cross-API lock — a slot is published only once the GPU has finished it and the four rotate,
  as on Linux. The shared State stays Frame Home's.
- The Environments panel runs frame-home --system and keeps it alive (one at a time, a pid file across panel
  restarts), the same systemEnv path as the Frame. The installer places/removes the proxy and marks the layer with a
  root/layer folder, in place of the old home-app registration and background pictures.
- Safe like the Vulkan layer: no home, or one stale over half a second, and the compositor draws Aurora as usual;
  the layer turns itself off after two unhealthy compositor starts, and root/layer/off turns it off by hand.

Linux keeps its Vulkan layer (unchanged). Verified without a headset on the null driver: the proxy loads and wraps
the compositor without crashing, recognises Aurora's shaders, and the frame hand-over completes (Frame Home connects,
imports the textures, renders). The compositor only draws the environment while presenting to a headset, so the final
on-headset image is the one step the null driver can't exercise.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/pc-steamvr.md

@@ -1,8 +1,10 @@
 # Frame Home on a PC (SteamVR)
 
-Frame Home also runs on a PC with SteamVR: the same renderer, homes and settings as on the Steam Frame, as SteamVR's
-environment whenever no game is open. The **Environments** panel in the Steam menu switches homes, as on the headset.
-It works with any headset SteamVR drives, including a Steam Frame streaming from the PC.
+Frame Home also runs on a PC with SteamVR, exactly the way it runs on the Steam Frame: a small layer inside SteamVR's
+compositor draws your home where it would draw Aurora, so your home *is* the SteamVR environment — it shows at boot,
+during game loads and behind the Steam menu, with the controllers and passthrough, never a separate app that launches
+and hands off. The **Environments** panel in the Steam menu switches homes, as on the headset. It works with any
+headset SteamVR drives, including a Steam Frame streaming from the PC.
 
 On a PC, Frame Home shows the environments in Frame Studio's **My Environments** (`Documents\Frame Studio\Environments`):
 save something in Studio and it's in VR straight away. Bundles (`.fbundle`) dropped there are unpacked by the panel.
@@ -26,16 +28,24 @@ and takes effect when SteamVR starts.
 
 ## How it works
 
-**Windows.** Frame Home becomes SteamVR's *home app*: SteamVR starts it whenever no game is open, and brings it back
-when a game quits. For the moments before it draws (SteamVR starting, a game closing) SteamVR shows its classic
-environment instead of Aurora, with its background set to a 360-degree picture of your current home taken from its
-spawn. So you see your home, not Aurora. The panel makes a new picture whenever you switch homes.
+Both platforms work the Steam Frame's way: a layer inside SteamVR's compositor draws your home in Aurora's place, and
+`frame-home --system` (which the Environments panel starts and keeps running) renders it. Because the swap happens
+inside the compositor, your home shows wherever Aurora would — at boot, during game loads, behind the Steam menu,
+with the controllers and passthrough — and steps aside for a game the instant it opens, coming back when it quits.
 
-**Linux.** Exactly the Steam Frame's way: a small Vulkan layer in SteamVR's compositor draws Frame Home in Aurora's
-place, and `frame-home --system` renders it. (Linux PCs are supported but haven't been tested on a desktop yet.)
+**Windows.** SteamVR's compositor is Direct3D 11, so the layer is a proxy `d3d11.dll` placed beside the compositor
+(`SteamVR\bin\win64`). It wraps the compositor's device, finds Aurora's own draws by their shader bytecode and draws
+the home over them; every other Direct3D call passes straight through to the real `d3d11.dll`, kept beside it as
+`fh_d3d11real.dll`. Frame Home renders in Vulkan and shares each frame to the compositor as a Direct3D 11 texture.
 
-The installer saves the SteamVR settings it changes (`enableHomeApp`, `environmentMode`, `background` and its
-projection) and puts them back exactly when you remove Frame Home.
+**Linux.** The same, as a Vulkan layer in the compositor (`layer/frame_home_layer.cpp`), since the Linux compositor
+is Vulkan. (Linux PCs are supported but haven't been tested on a desktop yet.)
+
+If the layer ever can't draw the home — Frame Home isn't running, or has stopped for more than half a second — the
+compositor draws Aurora as usual, so Frame Home stopping or crashing never blanks the headset. The layer turns itself
+off if the compositor starts twice without a healthy frame, and `%LOCALAPPDATA%\Frame Home\layer\off` turns it off by
+hand. The installer saves the SteamVR settings it changes (`enableHomeApp`, `environmentMode`) and puts them back,
+and removing the two files from `SteamVR\bin\win64` takes the layer off entirely.
 
 ## Files
 
@@ -44,15 +54,19 @@ projection) and puts them back exactly when you remove Frame Home.
 | `%LOCALAPPDATA%\Frame Home\bin` | `frame-home.exe`, `frame-switcher.exe` |
 | `%LOCALAPPDATA%\Frame Home\current` | the environment shown |
 | `%LOCALAPPDATA%\Frame Home\settings.json` | Frame Home's settings (the panel's Settings page) |
-| `%LOCALAPPDATA%\Frame Home\logs` | logs |
-| `%LOCALAPPDATA%\Frame Home\background` | the picture SteamVR shows while Frame Home starts |
+| `%LOCALAPPDATA%\Frame Home\logs` | logs (`frame-home.log` the renderer, `frame-layer.log` the compositor layer) |
+| `%LOCALAPPDATA%\Frame Home\layer` | the layer's off switch and crash guard; its folder marks the layer installed |
 | `Documents\Frame Studio\Environments` | the environments |
+| `SteamVR\bin\win64\d3d11.dll`, `fh_d3d11real.dll` | the compositor layer and the real Direct3D 11 beside it |
 
 On Linux everything is in `~/frame-home`, as on the headset.
 
 ## Troubleshooting
 
-- **Aurora still shows after installing:** SteamVR was running with its settings window open; restart SteamVR.
+- **Aurora still shows after installing:** the layer loads when the compositor starts, so restart SteamVR (or your
+  headset) once after installing. If it still shows, see `frame-layer.log`.
 - **Nothing in the Steam menu:** the panel starts with SteamVR. In SteamVR's settings, **Startup / Shutdown > Choose
   Startup Overlay Apps** should list **Environments** switched on.
 - **Black world:** Frame Home needs a GPU with Vulkan 1.2. Its log is `%LOCALAPPDATA%\Frame Home\logs\frame-home.log`.
+- **Turn it off without uninstalling:** make a file `%LOCALAPPDATA%\Frame Home\layer\off` (the layer checks every
+  second and draws Aurora); delete it to turn the home back on.