Merge main into flat2vr-mods

# Conflicts: # README.md # ui/index.html # ui/server.py
UEVR: address the second review; recheck on the Frame
2026-10-06 01:00:18 +02:00 · 2026-09-29 13:07:33 +10:00 · 2026-09-29 13:04:12 +10:00 · 2026-09-29 12:53:28 +10:00 · 2026-09-29 11:52:02 +10:00
10 changed files with 1157 additions and 28 deletions
@@ -217,7 +217,7 @@ Frame's software fits together, all checked against a real headset and labelled
 | [Install links for websites](docs/web-install.md) | `frame-control://install` links and manifests, the rules, a button to paste |
 | [VR comfort and HUD](docs/vr-utilities.md) · [Steam games](docs/steam-games.md) · [VR video](docs/vr-video.md) · [WebXR in Chromium](docs/webxr-chromium.md) | Installing and buying, watching VR180/360, the Chromium build |
 | [Mac in the headset](docs/mac-in-headset.md) | Mac windows and screens as panels in the Frame, with laser and keyboard input |
-| [VR mods and custom songs](docs/mods.md) | Per-game feasibility, real-Frame results and blockers; no installer yet |
+| [VR mods and custom songs](docs/mods.md) | UEVR for Unreal games from Frame Control (install, play in VR, remove), the per-game table, Beat Saber blockers |
 | [SSH](docs/ssh.md) · [Streaming](docs/streaming.md) · [Files](docs/file-transfer.md) · [Panels](docs/panels.md) · [Tailscale](docs/tailscale.md) | Topic notes |
 | [Frame Control for iPhone](docs/iphone.md) | The iPhone and iPad app, how it runs the server on the Frame, pairing |
 | [Recovery and OS images](docs/recovery-and-images.md) | Where to download the Frame's OS, what's inside, testing without the headset |
@@ -0,0 +1,122 @@
+# UEVR from Frame Control, 2026-09-29
+
+**Verified observations**, with limits below. Same device and software as
+[2026-09-28](mods-2026-09-28.md): aarch64, SteamOS `0.4.1`, BUILD_ID
+`20260925.6191901`, Proton `11.0-2c` ARM64, SteamVR `2.18.1`. Times are the
+Frame's AEST clock. Headset tests ran under the shared
+`/tmp/frame-test.lock`, taken 11:13–11:28, 11:33–11:49, 12:02–12:40,
+12:44–12:52 and 13:01–13:03. Battery 45 % →
+93 %, on charge throughout.
+
+**Not observed:** the VR image, head tracking and controller input. SteamVR
+reported `activity_level` 3 (user interaction timeout; the headset was not
+being worn) with `average_target_fps` 1. Every `frame_vrshot.py` stereo
+capture was a uniform dark frame. Frame submits prove the app is presenting
+to SteamVR, not that the image is correct.
+
+## Manual injection (11:13–11:28)
+
+Game launched with `steam steam://rungameid/1067310`. `UEVRInjector.exe` was
+started with the game process's Wine variables, and its WPF window drew
+through DXVK's D3D9. It listed `Drop-Win64-Shipping (pid: 320) (SkyArk
+(64-bit, PCD3D_SM5))`, a Wine-side process id.
+
+- `--attach=Drop-Win64-Shipping` didn't inject. The button still read
+  **Inject**, and the saved `OpenVRRadio=True` in `AppData/Local/praydog/…/user.config`
+  was not restored on the next start.
+- XTest clicks landed on the game: `XQueryPointer` reported child
+  `0x2000001` (the game) at the injector's coordinates, and
+  `XLowerWindow`/`XRaiseWindow`/`XSetInputFocus` didn't change that.
+- `XSendEvent` button events to the injector window worked. After OpenVR and
+  Inject, `/proc/<game>/maps` contained
+  `drive_c/frame26/uevr/UEVRBackend.dll` and `openvr_api.dll`, next to
+  Proton's `vrclient_x64.dll`. UEVR's log:
+
+```text
+[11:17:32.948] Hooking D3D11
+[11:17:33.020] Hooked DirectX 11
+[11:17:34.263] Framework initialized
+[11:17:34.475] [VR] Requested runtime: openvr_api.dll
+[11:17:39.791] UGameViewportClient::Draw called for the first time.
+[11:17:39.792] is stereo enabled called!
+```
+
+It also logged repeated `Failed to initialize Framework on DirectX 12` (probing
+before it chose D3D11) and failed Unreal scans, for example `Failed to locate
+r.EnableStereoEmulation cvar` and `Failed to find FSceneView constructor`.
+SteamVR loaded UEVR's action manifest and `bindings_oculus_touch.json` for
+`steam.app.1067310`. `vrcmd --stats` then showed `"key" :
+"steam.app.1067310"` with `frame_submits` 4439, then 5506 a few seconds later.
+
+A second session's injector exited within about 20 seconds. The third,
+started fresh, injected again (`frame_submits` 1412). After the game was
+stopped, a plain launch had no UEVR modules and no SteamVR scene app. All test
+files were removed.
+
+## Through Frame Control (11:33–11:49)
+
+Local `ui/server.py` against the `frame` alias. First the API, then the
+page's **VR mod** dialog, driven with a headless Chromium:
+
+| Step | Result |
+|---|---|
+| `status` for 2177750 (HL2 VR) | `eligible: false`; `install` refused ("doesn't look like an Unreal Engine game") |
+| `install` for 1067310 | 3 s. Three downloads, hashes matched, receipt written |
+| `start`, game running | First run refused: `the UEVR window is 960 px wide, not 625`. It was measured before WPF laid it out; `start` now waits for the width to settle. Rerun: injected, `frame_submits` 27 (36 s) |
+| `uninstall` while running | Refused: "the game is running; quit it first" |
+| `start`, game not running | Launched the game, injected, `frame_submits` 45 (55 s) |
+| UI: Remove, Install | Worked; the prefix listing matched its pre-install state except an empty `UnrealVRMod`, which uninstall now also removes |
+| UI: Play in VR | Failed once: the injector died with `Process terminated. … Resource name: Arg_AccessViolationException`, after `Fontconfig error: No writable cache directories` (it had no `HOME`). Fixed by keeping the normal environment under the game's (the relaunch-on-failure added next is gone with the GUI injector; see below) |
+| UI: Play in VR ×4 | 4 of 4 injected. The three cold starts took 54, 58 and 58 s; frame submits 56, 71, 80 |
+| UI: Remove | `drive_c`, `AppData/Roaming` and `AppData/Local` listings matched the pre-install state; download cache and receipt gone |
+
+## The GUI injector wasn't reliable (12:02–12:40)
+
+After review fixes, cold starts through the API with UEVR's own injector:
+
+- Batches of 4, 6 and 8 runs: 3/4, 4/6 and 6/8 injected. A retry that
+  relaunched the injector didn't rescue a bad session. In both failures of
+  the last batch, the first injector ignored the clicks and the next two
+  never showed a window within 60 s.
+- Captures of the ignoring injector (`xwd`) showed its first-drawn frame,
+  with OpenVR still unselected. The injector's log had no error.
+
+Lock released at 12:40 before redesigning.
+
+## Frame Control's own injector (12:44–12:52)
+
+`start` now runs `frame_inject.py` under python.org's embeddable Python
+3.14.7 (SHA-256 `d297e5ff…1f15`, matching python.org's release-file API), in
+the game's Wine session. The old install was removed and the new one
+installed without the headset lock, since neither launches anything. The
+prefix listing after removal matched the pre-install state; the new install
+is 47 MB.
+
+| Step | Result |
+|---|---|
+| API `start`, cold | Injected in 35 s, `frame_submits` 39. UEVR log: `Hooked DirectX 11`, `Framework initialized`, `Requested runtime: openvr_api.dll`; `config.txt` has `Frontend_RequestedRuntime=openvr_api.dll` |
+| API `start` ×8, cold | **8/8** injected, 33–34 s each; `frame_submits` 33–42 at the check |
+| UI: dialog while running | "UEVR is running in the game now." Remove disabled (screenshot in `docs/img/uevr-dialog.png`) |
+| UI: Remove → Install → Play in VR → Remove | Each worked; Play in VR injected (`frame_submits` 106 a few seconds later) |
+| After the last Remove | `drive_c`, `AppData/Roaming` and `AppData/Local` listings matched the pre-install state; download cache and receipts gone; no game or `python.exe` processes. The empty `/tmp/frame-control-mods.lock` was deleted by hand (tmpfs) |
+
+Battery 98–100 % on charge. Lock released at 12:52.
+
+## After the second review (13:01–13:03)
+
+`frame_inject.py` now declares every Win32 signature, checks each result,
+frees its remote buffers and closes its handles; uninstall accepts only our
+folder and UEVR's own settings folders. Rechecked: install; three cold starts
+injected in 35, 34 and 33 s (`frame_submits` 42, 38, 47), UEVR logging
+`Framework initialized` and `Requested runtime: openvr_api.dll`; uninstall
+left `drive_c`, `AppData/Roaming` and `AppData/Local` as before, with no cache,
+receipts or processes. Frame Control's injector total: 12 of 12 cold starts
+through the API, plus the UI run.
+
+## Left on the Frame
+
+- Gravitas (free, 7.4 GB, installed 2026-09-28 for this work) is still
+  installed; nothing else from this work is left.
+- No `UEVRInjector.exe` or game processes were left running. Steam and
+  SteamVR were running at the end.
+- The test lock was released at 13:03.
@@ -52,6 +52,7 @@ Lepton (Android 11, podman container "lepton-dev") ← its own panel, app 305600
 | The Steam client runs with `-cef-enable-debugging`, so its UI answers Chrome DevTools on loopback `127.0.0.1:8080`. The `SharedJSContext` page has `appStore` (owned apps), `downloadsStore` and `SteamClient.*`. `steam steam://install/<appid>` over SSH installs an owned game; when the options dialog shows (state 7), `SteamClient.Installs.ContinueInstall()` accepts it. **Verified 2026-09-25** with Balatro and Broforce. The Frame rating is `steam_hw_compat_category_packed >> 8 & 3`. | [steam-games.md](steam-games.md), `ui/frame_steam.py` |
 | Chromium Flatpak 154 has **no immersive WebXR**: `navigator.xr` exists, but `isSessionSupported("immersive-vr")` returns `false`. Web VR180 players (DL8/DeoVR embeds) still play video inline as a flat, pannable view, and their VR button opens a tab on immersiveweb.dev. Forcing it doesn't help. `--enable-features=OpenXR,WebXR --force-webxr-runtime=openxr`, with `/opt/steamvr` and `XR_RUNTIME_JSON` exposed to the Flatpak, still returns `false`. The aarch64 Linux binary has no OpenXR code at all (no `XR_RUNTIME_JSON`, `xrGetInstanceProcAddr` or loader strings), even though `chrome://flags` lists `#webxr-runtime` → OpenXR. **Why (verified against source 2026-09-25):** M154 is the first release that compiles OpenXR on Linux (`enable_openxr` includes `is_linux`, `checkout_openxr` is true in Flathub's tarball, and Flathub's GN args don't turn it off). But `content/services/isolated_xr_device/xr_runtime_provider.cc` only creates an OpenXR device under `ENABLE_OPENXR && IS_WIN`, on 154, 155 and `main`. Nothing on Linux calls the OpenXR code, so the linker drops it. The missing pieces are two unmerged Gerrit CLs (bug 506004811): [8132979](https://chromium-review.googlesource.com/c/chromium/src/+/8132979) wires the provider on Linux (with `kOpenXR` still off by default, so it needs `--enable-features=OpenXR`), and [8441736](https://chromium-review.googlesource.com/c/chromium/src/+/8441736) runs the XR service in a sandbox that allows SteamVR's sockets. The Frame does have an aarch64 runtime: `~/.config/openxr/1/active_runtime.json` → SteamVR `bin/linuxarm64/vrclient.so`. To watch in 3D, use a native player, or a Chromium built with those two CLs ([webxr-chromium.md](webxr-chromium.md)). That build (156.0.8071.0, arm64) reports `immersive-vr` as supported and starts a session that SteamVR takes as its scene app. With the headset on, the WebXR samples scene and three.js's stereo 360 video demo showed in 3D (verified 2026-09-26, seccomp sandbox off). Started with `--remote-debugging-port=9222`, Chromium answers DevTools on loopback. **Verified 2026-09-25**, BUILD_ID 20260922.6101926. | Web video, [panels.md](panels.md) |
 | **DeoVR (Steam app 837380, Windows/Unity) runs immersively** under Proton ARM64 + FEX: Unity's OpenVR XR plugin finds `OpenVR Headset(Steam Frame)` and the `frame_controller`, the GPU shows as Turnip Adreno 750, and AVPro Video decodes through `MF-MediaEngine-Hardware`. It played 7680×3840 and 8192×4096 H.265 VR180 SBS streams in dome/fisheye mode (`FirstFrameReady`). Unity's own `VideoPlayer` (used for grid thumbnails) fails with `0xc00d36bb`, so thumbnail previews stay blank. The first launch takes about 45 s (`ComputeShaders: InitAsync`). Log: `compatdata/837380/pfx/drive_c/users/steamuser/AppData/LocalLow/Deo VR/Deo VR/Player.log`. **Verified 2026-09-25**, BUILD_ID 20260922.6101926. | [vr-video.md](vr-video.md) |
+| **A second Windows program can join a running Proton game.** Copy `WINEPREFIX`, `WINEDLLPATH`, `WINEDLLOVERRIDES`, `PATH` (Proton's `files/bin-arm64` comes first) and `DISPLAY` from `/proc/<game pid>/environ`, keeping your own `HOME` and the rest, and run `wine prog.exe` from an ordinary SSH shell. It shares the game's wineserver (outside the pressure-vessel container). Don't copy `WINESERVERSOCKET`, which is an inherited fd. A game's windows live on gamescope's X display for that app (`:1` for Gravitas), where the full-screen game keeps the pointer and focus: XTest clicks and restacking don't reach other windows, but `XSendEvent` button events sent to a window do. `xwd` captures WPF/DXVK windows but shows Vulkan game windows as black. **Verified 2026-09-29**, BUILD_ID 20260925.6191901, Proton 11.0-2c ARM64. | [mods.md](mods.md) |
 | **Wolvic (VR browser APK) runs in Lepton against SteamVR's OpenXR**, with limits. The stock Lynx build aborts (`Runtime doesn't support selected swapChain color format`: it wants `GL_RGBA8`), and the stock Quest build fails with `XR_ERROR_API_VERSION_UNSUPPORTED`. Patching `DeviceDelegateOpenXR::GetSwapChainCreateInfo` in the Lynx build's `libnative-lib.so` to `GL_SRGB8_ALPHA8` (0x8C43) and re-signing fixes start-up. The Gecko engine then segfaults in `libxul`. The Chromium-engine build (Lynx v1.3-chromium) browses fine as an immersive app. Its page reports `isSessionSupported("immersive-vr") == true`, and `requestSession` succeeds, running about 36 rAF/s, but the headset shows **black** for WebXR content, or Wolvic's loading spinner that never clears, until the session is ended. Video decodes on the software `OMX.google.h264.decoder`. Tapping the URL bar's selection menu crashes it (no clipboard service). Open URLs with `am start -a VIEW -n com.igalia.wolvic/.VRBrowserActivity -d <url>` over the instance's ADB. DevTools is at `localabstract:content_shell_devtools_remote`. **Verified 2026-09-25**, BUILD_ID 20260922.6101926. | Web VR video, [apks.md](apks.md) |
 | Tailscale runs without root as a userspace `tailscaled` user service (static arm64 build in `~/.local/share/tailscale`, lingering on). In userspace mode, inbound tailnet connections reach the Frame's **loopback**, so every port, including DevTools on 8080, is reachable from the tailnet. **Verified 2026-09-25.** | [tailscale.md](tailscale.md), `scripts/tailscale-on-frame.sh` |
 | **T3 Code desktop runs natively.** The stock release `T3-Code-0.0.42-arm64.AppImage` in `~/Applications/T3CodeDesktop/` starts with no extra setup: glibc 2.39, `libfuse.so.2`, GTK 3, NSS and libsecret are on the image. `panel-on-frame.sh --name t3code-desktop -- '~/Applications/T3CodeDesktop/T3-Code.AppImage'` gives it its own panel (`valve.steam.desktopgame.2000281357`, `--ozone-platform=x11`). Its bundled server listens on `127.0.0.1:3773` and shows up in onboarding as the `frame` computer, with `passwordStore: gnome-libsecret`. The image has no agent CLI and no `node`. Agents run through the LAN CLIProxyAPI (`llm-proxy.lan:8317`, which resolves on the Frame). Claude Code 2.1.283 comes from `claude.ai/install.sh`, and Codex 0.157.1 from the `codex-aarch64-unknown-linux-musl` release tarball, both into `~/.local/bin`. `with-cliproxy` and a mode-600 `~/.config/cliproxyapi/secrets.env` are copied from the Mac. The wrappers `claude-cliproxy` and `codex-cliproxy` (a `-c model_provider=cliproxy`, `wire_api="responses"`, `env_key="CLIPROXY_API_KEY"`) are set as `providers.claudeAgent.binaryPath` and `providers.codex.binaryPath` in `~/.t3/userdata/settings.json`, and T3 picked that up without a restart. Through the wrappers, `claude auth status` reports `loggedIn: true` (`oauth_token`), and both CLIs answered a prompt with `kimi-k3`. `gamescopectl screenshot` captured another layer (the Lepton T3 app) rather than this panel. `DISPLAY=:0 xwd -id <win>` piped to `ffmpeg` captures the window itself (1920×1080). **Verified 2026-09-26**, BUILD_ID 20260922.6101926. | Running T3 Code as a host on the Frame |
@@ -1,11 +1,14 @@
 # Flat-to-VR mods and Beat Saber songs

-**Status: feasibility work, not an installer.** Frame Control does not yet
-manage mods or Beat Saber songs. [Issue #26](https://github.com/saphid/frame-control/issues/26)
-stays open: neither UEVR injection nor Beat Saber custom-song playback has
-been verified on this Frame. Alex has an owned copy on a Quest 2; that copy
-has not been inspected. There is no Mods button until the underlying
-install, playback and removal have been checked.
+**Status: UEVR works from Frame Control for Unreal Engine games; Beat Saber
+songs are blocked.** Installed games have a **VR mod** button. It installs
+UEVR, starts the game with UEVR injected, and removes UEVR again. That whole
+loop was run on a real Frame on 2026-09-29 with Gravitas, from the app's own
+UI ([evidence](evidence/mods-2026-09-29.md)). The headset was unworn, so
+the VR image, head tracking and controls haven't been seen yet. Beat Saber
+custom songs need an owned Beat Saber on the Frame, which there isn't
+([below](#beat-saber-songs-first)).
+[Issue #26](https://github.com/saphid/frame-control/issues/26) stays open for those.

 The mod manager must be Frame Control's own implementation. Mods and songs
 are permitted third-party content; BSManager, ModsBeforeFriday, MO2 and other
@@ -15,27 +18,87 @@ unofficial mod mirrors are part of this work.

 ## Per-game support

-Checked 2026-09-28 on SteamOS **0.4.1**, BUILD_ID **20260925.6191901**, aarch64,
-with **Proton 11.0-2c ARM64** and SteamVR **2.18.1**. “Verified” describes only
+Checked 2026-09-28 and 2026-09-29 on SteamOS **0.4.1**, BUILD_ID
+**20260925.6191901**, aarch64, with **Proton 11.0-2c ARM64** and SteamVR **2.18.1**. “Verified” describes only
 the observation stated, not a promise that the game is playable. “Documented”
 means an upstream source describes it; “inferred” means it still needs a test.

 | Game / build | Mod or content | Evidence and support status | Next check |
 |---|---|---|---|
 | Half-Life 2: VR Mod – Episode One, Steam 2177750, build 25413453 | Official Steam community mod, shared base depot 658920 build 25413418 | **Verified: startup only.** Already installed; launched through Proton ARM64. The stereo headset capture showed its first-time setup, and SteamVR loaded `bindings_frame.json`. Gameplay, controller interaction, fresh installation and removal are unverified. | Complete first-time setup and play a level before offering a tested install shortcut. |
-| Gravitas, Steam 1067310, Windows | UEVR 1.05 | **Verified: prerequisites and windows only.** Free Steam install completed. The game produced a `SkyArk (64-bit, PCD3D_SM5)` window. UEVR needed .NET; with official .NET 6.0.36 libraries it produced a `UEVR` window. A combined run exited 1 with X11 errors before injection was verified. **Inferred: compatibility remains unknown**, not proven broken. | Retry during a stable headset session; verify injection, stereo scene output, controls and removal. |
+| Gravitas, Steam 1067310, Windows, Unreal Engine 4 | UEVR 1.05, from Frame Control | **Verified 2026-09-29: installs, injects, SteamVR receives frames, removes cleanly.** Twelve cold **Play in VR** runs (33–35 s each), and the full cycle from the app's UI, all loaded `UEVRBackend.dll` into the game, with UEVR logging `Hooked DirectX 11` and `Requested runtime: openvr_api.dll`. SteamVR's compositor counted frame submits for `steam.app.1067310`. Remove restored the prefix to its pre-install file listing. **Not seen:** the stereo image, head tracking and controls (headset unworn). | Wear the headset: check the image, tracking, UEVR's in-headset menu and controller input. |
 | Beat Saber, Steam 620980, Windows / Proton | Basic custom songs; later SongCore and version-matched mods | **Verified: absent from the 868-game library returned by this Frame.** Store metadata lists Windows, not Linux. **Documented:** the PC game reads basic maps from `Beat Saber_Data/CustomLevels` without a mod manager. Playback on Frame is unverified. | An already-owned, legitimately installed copy is required. Do not buy it as part of this task. |
 | Beat Saber, claimed native ARM64 build | Custom songs / native mods | **Inferred: unverified.** The research mentions this build but supplies no verified official distributable or tested layout. CPU architecture alone does not identify Android versus Linux, the game version or the mod ABI. | Establish official provenance, ownership, binary type and version before touching files. Do not apply Quest patches to an unidentified build. |
-| Beat Saber, Alex's Quest 2 copy | Custom songs / Android mods | **Documented: owner-reported copy on Quest 2**, currently charging. No APK, version or installed mods inspected; no Frame playback verified. This does not establish ownership of the Steam build. | When the Quest is available, inspect the owned copy's version and supported transfer path, then test Lepton/OpenXR compatibility without bypassing entitlement checks. |
+| Beat Saber, Alex's Quest 2 copy | Custom songs / Android mods | **Documented: owner-reported copy on Quest 2.** Not reachable on 2026-09-29 (no device on `adb` from the Mac). No APK, version or installed mods inspected; no Frame playback verified. A Quest copy is a Meta store purchase; copying it to another headset would need its entitlement check to pass there, which this work won't work around. This does not establish ownership of the Steam build. | When the Quest is available, inspect the owned copy's version and supported transfer path, then test Lepton/OpenXR compatibility without bypassing entitlement checks. |
 | Hogwarts Legacy, Steam 990080 | R.E.A.L. | **Verified: listed in this Frame's owned library, not installed.** Official release access and redistribution permission were not established; the referenced author Patreon page returned HTTP 403. No archive downloaded or game tested. | Obtain a current free release from the author and confirm its terms before any test. A news report saying “free” is not a redistribution grant. |
 | Horizon Zero Dawn, Steam 1151640; Horizon Forbidden West, Steam 2420110 | R.E.A.L. | **Verified: both listed as owned, neither installed.** Same source/permission blocker as above; runtime support is unverified. | Check each game's supported version against an accessible official release. |
 | Half-Life 2 VR / other OpenVR games | OpenComposite, per-game replacement | **Documented:** forwards OpenVR calls to OpenXR. **Inferred: Frame compatibility unknown.** Not installed or tested. HL2 VR reached setup with the shipped OpenVR path already. | Test a specific game and replacement DLL only if needed; preserve its original DLL. Never switch the shared headset's runtime globally. |
 | Doom / Quake / Half-Life Team Beef ports | Author's VR ports plus separately owned or free game data | **Inferred: untested.** Android ARM64 support does not establish OpenXR extension or controller compatibility on Lepton. | Choose an official release and legally usable data set, then test that exact port. |
 | Skyrim VR, Steam 611670 | SKSEVR / HIGGS / PLANCK stack | **Verified: Skyrim VR is absent from this library.** Owning flat Skyrim or Special Edition is not the VR game's entitlement. Runtime and mod support are unverified. | An already-owned VR copy and version-matched official mod releases are required. |

-The [test record](evidence/mods-2026-09-28.md) distinguishes process startup,
-visible output and failures. It also records a SteamVR restart during the
-shared session, which prevents attributing the failed UEVR attempt to FEX.
+The test records ([2026-09-28](evidence/mods-2026-09-28.md),
+[2026-09-29](evidence/mods-2026-09-29.md)) distinguish process startup,
+visible output, injection and failures.
+
+## UEVR from Frame Control
+
+![The VR mod dialog while UEVR runs in Gravitas](img/uevr-dialog.png)
+
+**Get games → an installed game → VR mod.** The dialog says whether the game
+can take UEVR, then offers **Install UEVR**, **▶ Play in VR** and **Remove
+UEVR**. The server route is `POST /api/mods {"action": "status" | "install" |
+"start" | "uninstall", "appid": …}`, and the work happens on the Frame in
+[`ui/frame_mods.py`](../ui/frame_mods.py). It uses only the standard library,
+like `frame_steam.py`.
+
+- **Which games.** Unreal Engine games, recognised by their
+  `…/Binaries/Win64/*-Win64-Shipping.exe` (inferred as the general rule; checked
+  with Gravitas, and HL2 VR is correctly refused). The game needs a Proton
+  prefix, so it must have been played once.
+- **Install.** Downloads praydog's [UEVR 1.05 release](https://github.com/praydog/UEVR/releases/tag/1.05)
+  and python.org's [Windows x64 embeddable Python 3.14.7](https://www.python.org/downloads/release/python-3147/).
+  Each is checked against a pinned SHA-256; Python's comes from python.org's
+  release-file API. Archives are unpacked into a staging folder, rejecting
+  entries that escape it, symlinks and oversized contents, then moved into
+  `<prefix>/drive_c/frame-control/` (about 47 MB). Nothing goes into the
+  game's own folder. A receipt in `~/.local/share/frame-control/mods/` lists
+  what to remove, including UEVR's own settings folders only if they didn't
+  exist before. Install and remove refuse while the game is running, and only
+  one mod action runs at a time.
+- **Play in VR.** Launches the game through Steam if it isn't running and
+  waits for its window. It then runs a short script under that Python, with
+  the game's Proton, prefix and Wine settings read from the game process, so
+  both share one Wine session. The script repeats what UEVR's own injector does
+  when you press Inject with OpenVR chosen: load `UEVRPluginNullifier.dll` and
+  call its `nullify`, load `openvr_api.dll`, set `Frontend_RequestedRuntime` in
+  UEVR's per-game `config.txt`, then load `UEVRBackend.dll`. Each load is a
+  `LoadLibraryW` remote thread, as in the frontend's `Injector.cs`. `start`
+  then checks that `UEVRBackend.dll` is mapped into the game and reads
+  SteamVR's frame count for the app (`vrcmd --stats`).
+- **Remove.** Deletes what the receipt lists, then the download cache once
+  no game uses it. Verified: the prefix's file listing matched its
+  pre-install state afterwards.
+
+Why not UEVR's own injector (verified 2026-09-29):
+
+- It's a .NET 6 WPF app, so it needs Microsoft's .NET runtimes (about 70 MB
+  of downloads) in the prefix.
+- Under gamescope, the full-screen game keeps the pointer and focus. XTest
+  clicks, raising or refocusing the injector window don't change that, so in
+  the headset you can't click it. Sending X `ButtonPress`/`ButtonRelease`
+  events straight to its window does work.
+- `--attach=<process>` didn't inject under Wine, and it didn't restore its
+  saved OpenVR choice.
+- Driven that way, it injected in 6 of 8 cold starts. In a bad session every
+  new injector ignored input or never showed its window, even after
+  relaunching. Its process list reads each process's main window title, a
+  cross-process window message; a window that isn't answering would block its
+  UI thread (inferred from the frontend's source, not proven). Without a
+  `HOME` it also died in .NET at startup.
+- Frame Control's own script injected in 12 of 12 cold starts through the API, in 33–35 s, and again from the UI.
+- UEVR's DirectX 12 probing logs errors before it settles on DirectX 11 for
+  Gravitas, and some of its Unreal engine scans fail on this older UE4 game.
+  Neither stopped the injection.

 ## Beat Saber: songs first

@@ -62,7 +125,10 @@ or dependency for Frame Control.

 ## Requirements for our manager

-These are **planned**, not implemented or verified:
+For UEVR, items 1–5 are implemented in `frame_mods.py` and covered by
+fake-library tests (`tests/test_mods.py`), apart from checking ownership
+through Steam; item 6 is met for Gravitas. Beat Saber songs would need the
+same, and none of it is built for them:

 1. Resolve the selected Steam game's real library, installed build, executable
   architecture and Proton prefix. Confirm ownership through Steam; a directory
@@ -91,7 +157,11 @@ These are **planned**, not implemented or verified:
 - [UEVR 1.05 official release](https://github.com/praydog/UEVR/releases/tag/1.05)
  and [author's usage instructions](https://github.com/praydog/UEVR#getting-started).
 - [Microsoft .NET 6 release metadata](https://builds.dotnet.microsoft.com/dotnet/release-metadata/6.0/releases.json),
-  including the SHA-512 hashes used for the test runtimes.
+  including the SHA-512 hashes used for the injector tests.
+- [UEVR frontend source](https://github.com/praydog/UEVR-Frontend): `UEVR/MainWindow.xaml.cs`
+  (`Inject_Clicked`) and `UEVR/Injector.cs`, the steps `frame_inject.py` follows.
+- [python.org release-file API](https://www.python.org/api/v2/downloads/release_file/) for the
+  embeddable Python's `sha256_sum`.
 - [OpenComposite's OpenXR branch](https://gitlab.com/znixian/OpenOVR/-/tree/openxr),
  including per-game installation and the need to preserve original DLLs.
 - [R.E.A.L. author post referenced by the research](https://www.patreon.com/realvr/posts/but-wheres-link-165840151)
@@ -4,9 +4,9 @@ Frame Control's **Get games** section lists the games you own with each one's
 Steam Frame rating, installs them on the Frame, and searches the Steam store.
 This page covers how it works underneath, so you can do the same from a shell.

-For flat-to-VR mods and Beat Saber custom songs, see the
-[per-game feasibility table](mods.md). Mod support is separate from Steam's
-Frame rating; there is no mod installer yet.
+Installed Unreal Engine games also have a **VR mod** button that installs,
+starts and removes UEVR; see [VR mods](mods.md) for how it works and the
+per-game table. Mod support is separate from Steam's Frame rating.

 ## How it works

@@ -0,0 +1,334 @@
+"""VR mod (UEVR) checks that need no headset or network: a fake Steam library on disk.
+
+Run: python3 -m unittest discover -s tests
+"""
+import hashlib
+import io
+import itertools
+import json
+import stat
+import subprocess
+import sys
+import tempfile
+import unittest
+import zipfile
+from pathlib import Path
+from unittest import mock
+
+ROOT = Path(__file__).resolve().parent.parent
+sys.path.insert(0, str(ROOT / "ui"))
+
+import frame_mods  # noqa: E402
+import test_server  # noqa: E402  (not `from … import`, or unittest runs ServerGuards twice)
+
+APPID = 1067310
+
+
+def zip_bytes(files, links=()):
+    buf = io.BytesIO()
+    with zipfile.ZipFile(buf, "w") as z:
+        for name, data in files.items():
+            z.writestr(name, data)
+        for name in links:
+            info = zipfile.ZipInfo(name)
+            info.external_attr = (stat.S_IFLNK | 0o777) << 16
+            z.writestr(info, "/etc/passwd")
+    return buf.getvalue()
+
+
+class FakeLibrary(unittest.TestCase):
+    """A Steam library with Gravitas's real layout, and pinned downloads served from memory."""
+
+    def setUp(self):
+        tmp = tempfile.TemporaryDirectory()
+        self.addCleanup(tmp.cleanup)
+        home = Path(tmp.name)
+        self.steam = home / ".local/share/Steam"
+        apps = self.steam / "steamapps"
+        (apps / "common/Gravitas/SkyArk/Binaries/Win64").mkdir(parents=True)
+        (apps / "common/Gravitas/SkyArk/Binaries/Win64/Drop-Win64-Shipping.exe").write_bytes(b"MZ" * 100)
+        (apps / "common/Gravitas/Drop.exe").write_bytes(b"MZ")
+        self.prefix = apps / f"compatdata/{APPID}/pfx"
+        for sub in ("Roaming", "Local"):
+            (self.prefix / "drive_c/users/steamuser/AppData" / sub).mkdir(parents=True)
+        (apps / f"appmanifest_{APPID}.acf").write_text(
+            f'"AppState"\n{{\n\t"appid"\t\t"{APPID}"\n\t"name"\t\t"Gravitas"\n\t"installdir"\t\t"Gravitas"\n}}\n')
+        for name, value in (("STEAM", self.steam), ("CACHE", home / ".cache/frame-control/mods"),
+                            ("RECEIPTS", home / ".local/share/frame-control/mods")):
+            p = mock.patch.object(frame_mods, name, value)
+            p.start()
+            self.addCleanup(p.stop)
+        self.running = None
+        p = mock.patch.object(frame_mods, "game_pid", side_effect=lambda exe: self.running)
+        p.start()
+        self.addCleanup(p.stop)
+        self.downloads = {frame_mods.UEVR["url"]: zip_bytes({"UEVRInjector.exe": b"MZ", "UEVRBackend.dll": b"MZ",
+                                                             "openvr_api.dll": b"MZ"})}
+        self.downloads[frame_mods.PYTHON["url"]] = zip_bytes({"python.exe": b"MZ", "python314.zip": b"PK"})
+        self.pin(self.downloads)
+
+    def pin(self, downloads):
+        """Serve these bytes and pin their real hashes in place of the published ones."""
+        for name in ("UEVR", "PYTHON"):
+            pinned = getattr(frame_mods, name)
+            p = mock.patch.object(frame_mods, name,
+                                  dict(pinned, sha256=hashlib.sha256(downloads[pinned["url"]]).hexdigest()))
+            p.start()
+            self.addCleanup(p.stop)
+        p = mock.patch.object(frame_mods.urllib.request, "urlopen",
+                              side_effect=lambda url, timeout: io.BytesIO(downloads[url]))
+        self.urlopen = p.start()
+        self.addCleanup(p.stop)
+
+    def managed(self):
+        return self.prefix / "drive_c/frame-control"
+
+
+class Status(FakeLibrary):
+    def test_unreal_game_is_eligible_and_not_installed(self):
+        st = frame_mods.status(APPID)
+        self.assertEqual((st["eligible"], st["exe"], st["installed"], st["running"], st["prefix"]),
+                         (True, "Drop-Win64-Shipping.exe", False, False, True))
+
+    def test_game_without_unreal_binary_is_refused(self):
+        (self.steam / "steamapps/common/Gravitas/SkyArk/Binaries/Win64/Drop-Win64-Shipping.exe").unlink()
+        self.assertFalse(frame_mods.status(APPID)["eligible"])
+        with self.assertRaisesRegex(frame_mods.Fail, "Unreal Engine"):
+            frame_mods.install(APPID)
+        self.urlopen.assert_not_called()
+
+    def test_uninstalled_game(self):
+        with self.assertRaisesRegex(frame_mods.Fail, "isn't installed"):
+            frame_mods.status(620)
+
+
+class InstallUninstall(FakeLibrary):
+    def test_install_then_uninstall_leaves_prefix_as_found(self):
+        before = sorted(p.relative_to(self.prefix) for p in self.prefix.rglob("*"))
+        res = frame_mods.install(APPID)
+        self.assertTrue(res["installed"])
+        self.assertTrue((self.managed() / "uevr-1.05/UEVRBackend.dll").is_file())
+        self.assertTrue((self.managed() / "python-3.14.7/python.exe").is_file())
+        self.assertIn("UEVRBackend.dll", (self.managed() / "python-3.14.7/frame_inject.py").read_text())
+        self.assertFalse(list(self.managed().glob(".staging-*")))
+        # What UEVR writes on its first injection.
+        roaming = self.prefix / "drive_c/users/steamuser/AppData/Roaming/UnrealVRMod/Drop-Win64-Shipping"
+        roaming.mkdir(parents=True)
+        (roaming / "log.txt").write_text("x")
+        (self.prefix / "drive_c/users/steamuser/AppData/Local/praydog/x").mkdir(parents=True)
+        frame_mods.uninstall(APPID)
+        after = sorted(p.relative_to(self.prefix) for p in self.prefix.rglob("*"))
+        self.assertEqual(after, before)
+        self.assertFalse(frame_mods.CACHE.exists(), "the downloads go once no game uses them")
+        self.assertIsNone(frame_mods.read_receipt(APPID))
+
+    def test_existing_uevr_settings_survive_uninstall(self):
+        profile = self.prefix / "drive_c/users/steamuser/AppData/Roaming/UnrealVRMod/Drop-Win64-Shipping"
+        profile.mkdir(parents=True)
+        (profile / "config.txt").write_text("mine")
+        frame_mods.install(APPID)
+        frame_mods.uninstall(APPID)
+        self.assertEqual((profile / "config.txt").read_text(), "mine")
+
+    def test_second_install_is_a_no_op(self):
+        frame_mods.install(APPID)
+        calls = self.urlopen.call_count
+        self.assertIn("already installed", frame_mods.install(APPID)["message"])
+        self.assertEqual(self.urlopen.call_count, calls)
+
+    def test_refuses_while_game_runs(self):
+        self.running = 4242
+        with self.assertRaisesRegex(frame_mods.Fail, "running"):
+            frame_mods.install(APPID)
+        self.running = None
+        frame_mods.install(APPID)
+        self.running = 4242
+        with self.assertRaisesRegex(frame_mods.Fail, "running"):
+            frame_mods.uninstall(APPID)
+        self.assertTrue((self.managed() / "uevr-1.05").is_dir())
+
+    def test_needs_a_prefix(self):
+        import shutil
+        shutil.rmtree(self.prefix.parent)
+        with self.assertRaisesRegex(frame_mods.Fail, "play it once"):
+            frame_mods.install(APPID)
+
+    def test_receipt_cannot_point_outside_the_prefix(self):
+        frame_mods.install(APPID)
+        r = frame_mods.read_receipt(APPID)
+        victim = self.steam / "steamapps/common/Gravitas"
+        r["remove"].append(str(self.prefix / "../../../common/Gravitas"))
+        frame_mods.receipt_path(APPID).write_text(json.dumps(r))
+        with self.assertRaisesRegex(frame_mods.Fail, "didn't create"):
+            frame_mods.uninstall(APPID)
+        self.assertTrue(victim.is_dir())
+        self.assertTrue((self.managed() / "uevr-1.05").is_dir(), "nothing removed when the receipt is bad")
+
+
+    def test_receipt_cannot_delete_other_things_in_the_prefix(self):
+        frame_mods.install(APPID)
+        r = frame_mods.read_receipt(APPID)
+        users = self.prefix / "drive_c/users"
+        r["remove"].append(str(users))
+        frame_mods.receipt_path(APPID).write_text(json.dumps(r))
+        with self.assertRaisesRegex(frame_mods.Fail, "didn't create"):
+            frame_mods.uninstall(APPID)
+        self.assertTrue(users.is_dir())
+
+    def test_failed_removal_keeps_the_receipt(self):
+        frame_mods.install(APPID)
+        with mock.patch.object(frame_mods.shutil, "rmtree"):  # e.g. a permission error, swallowed
+            with self.assertRaisesRegex(frame_mods.Fail, "couldn't remove"):
+                frame_mods.uninstall(APPID)
+        self.assertIsNotNone(frame_mods.read_receipt(APPID), "Remove can be tried again")
+        frame_mods.uninstall(APPID)
+        self.assertFalse(self.managed().exists())
+
+    def test_receipt_cannot_name_another_prefix(self):
+        frame_mods.install(APPID)
+        r = frame_mods.read_receipt(APPID)
+        r["prefix"] = "/"
+        frame_mods.receipt_path(APPID).write_text(json.dumps(r))
+        with self.assertRaisesRegex(frame_mods.Fail, "isn't app"):
+            frame_mods.uninstall(APPID)
+        self.assertTrue((self.managed() / "uevr-1.05").is_dir())
+
+
+class Downloads(FakeLibrary):
+    def test_hash_mismatch_deletes_and_installs_nothing(self):
+        self.downloads[frame_mods.UEVR["url"]] = zip_bytes({"UEVRBackend.dll": b"tampered"})
+        with self.assertRaisesRegex(frame_mods.Fail, "doesn't match"):
+            frame_mods.install(APPID)
+        self.assertFalse((frame_mods.CACHE / "UEVR.zip").exists())
+        self.assertFalse(self.managed().exists())
+        self.assertIsNone(frame_mods.read_receipt(APPID))
+
+    def test_archive_escaping_its_folder_is_refused(self):
+        for bad in (zip_bytes({"UEVRBackend.dll": b"MZ", "../../evil.dll": b"MZ"}),
+                    zip_bytes({"UEVRBackend.dll": b"MZ"}, links=["openvr_api.dll"])):
+            downloads = dict(self.downloads, **{frame_mods.UEVR["url"]: bad})
+            self.pin(downloads)
+            with self.subTest(), self.assertRaises(frame_mods.Fail):
+                frame_mods.install(APPID)
+            self.assertFalse((self.prefix / "drive_c/evil.dll").exists())
+            self.assertFalse(list(self.managed().glob("*")) if self.managed().exists() else [])
+            import shutil
+            shutil.rmtree(frame_mods.CACHE, ignore_errors=True)
+
+    def test_oversized_archive_is_refused(self):
+        with mock.patch.object(frame_mods, "MAX_UNPACKED", 3):
+            with self.assertRaisesRegex(frame_mods.Fail, "more than expected"):
+                frame_mods.install(APPID)
+
+
+    def test_oversized_download_is_stopped(self):
+        with mock.patch.object(frame_mods, "MAX_DOWNLOAD", 10):
+            with self.assertRaisesRegex(frame_mods.Fail, "bigger than expected"):
+                frame_mods.install(APPID)
+        self.assertFalse(list(frame_mods.CACHE.glob("*")))
+
+
+class Actions(FakeLibrary):
+    def test_one_change_at_a_time(self):
+        lock = Path(tempfile.mkdtemp()) / "mods.lock"
+        with mock.patch.object(frame_mods, "LOCK", lock), open(lock, "w") as held:
+            frame_mods.fcntl.flock(held, frame_mods.fcntl.LOCK_EX)
+            with self.assertRaisesRegex(frame_mods.Fail, "another mod action"):
+                frame_mods.main(["install", str(APPID)])
+            self.assertFalse(frame_mods.status(APPID)["installed"])
+            self.assertEqual(frame_mods.main(["status", str(APPID)])["appid"], APPID, "status never waits")
+
+    def test_zero_frames_is_an_answer(self):
+        stats = json.dumps([{"key": f"steam.app.{APPID}", "frame_submits": 0}, {"operation": "status"}])
+        with mock.patch.object(frame_mods.subprocess, "run", return_value=mock.Mock(stdout=stats)):
+            self.assertEqual(frame_mods.wait("frames", 5, lambda: frame_mods.frame_submits(APPID)), 0)
+        with mock.patch.object(frame_mods.subprocess, "run", return_value=mock.Mock(stdout='{"odd": 1}')):
+            self.assertIsNone(frame_mods.frame_submits(APPID))
+
+
+class Start(FakeLibrary):
+    def environ(self, text):
+        """The game's /proc/<pid>/environ; every other file reads normally."""
+        real = frame_mods.Path.read_text
+        return mock.patch.object(frame_mods.Path, "read_text", autospec=True, side_effect=lambda path, *a, **k:
+                                 text if str(path).startswith("/proc/") else real(path, *a, **k))
+
+    def test_needs_install_first(self):
+        with self.assertRaisesRegex(frame_mods.Fail, "isn't installed"):
+            frame_mods.start(APPID)
+
+    def run_start(self, reply, loaded=(False, True, True, True)):
+        frame_mods.install(APPID)
+        self.running = 4242
+        env = "WINEPREFIX=/x\0DISPLAY=:1\0WINESERVERSOCKET=17\0PATH=/p\0"
+        with self.environ(env), \
+                mock.patch.object(frame_mods, "loaded", side_effect=list(loaded) + [True] * 5), \
+                mock.patch.object(frame_mods, "x11_windows", return_value=[(1, "SkyArk", 1280)]), \
+                mock.patch.object(frame_mods.subprocess, "run", return_value=mock.Mock(stdout=reply, stderr="")) as run, \
+                mock.patch.object(frame_mods, "frame_submits", return_value=7), \
+                mock.patch.object(frame_mods.time, "sleep"):
+            return frame_mods.start(APPID), run
+
+    def test_injects_with_the_games_wine_settings(self):
+        res, run = self.run_start('noise\n{"pid": 320}\n')
+        self.assertEqual((res["frame_submits"], res["message"]), (7, "UEVR injected into Gravitas; SteamVR is receiving its frames"))
+        cmd, env = run.call_args.args[0], run.call_args.kwargs["env"]
+        self.assertEqual(cmd[:2], ["wine", "C:\\frame-control\\python-3.14.7\\python.exe"])
+        self.assertEqual(cmd[3:], ["Drop-Win64-Shipping.exe", "C:\\frame-control\\uevr-1.05",
+                                   "C:\\users\\steamuser\\AppData\\Roaming\\UnrealVRMod\\Drop-Win64-Shipping"])
+        self.assertEqual(env["WINEPREFIX"], "/x")
+        self.assertNotIn("WINESERVERSOCKET", env, "an inherited fd number means nothing to a new process")
+        self.assertIn("HOME", env, "fontconfig needs a HOME for its cache")
+
+    def test_reports_the_injection_error(self):
+        with self.assertRaisesRegex(frame_mods.Fail, "couldn't open"):
+            self.run_start('{"error": "couldn\'t open Drop-Win64-Shipping.exe (5)"}\n')
+
+    def test_success_is_checked_in_the_game(self):
+        with self.assertRaisesRegex(frame_mods.Fail, "has no UEVRBackend.dll"):
+            with mock.patch.object(frame_mods.time, "time", side_effect=itertools.count(0, 5)):
+                self.run_start('{"pid": 320}\n', loaded=[False] * 40)
+
+    def test_inject_script_is_valid_python(self):
+        compile(frame_mods.INJECT_PY, "frame_inject.py", "exec")
+
+
+class Helper(unittest.TestCase):
+    def test_unexpected_errors_are_still_json(self):
+        # A receipt from another version, without "exe": a KeyError, not a traceback.
+        script = (ROOT / "ui" / "frame_mods.py").read_text().replace(
+            "def read_receipt(appid):", "def read_receipt(appid):\n    return {'prefix': '/x'}\n\n\ndef _unused(appid):")
+        out = subprocess.run([sys.executable, "-", "uninstall", "1"], input=script,
+                             capture_output=True, text=True, timeout=30, env={"HOME": tempfile.mkdtemp()})
+        self.assertEqual(out.returncode, 1, out.stderr)
+        self.assertIn("KeyError", json.loads(out.stdout)["error"])
+
+    def test_bad_usage_prints_json_error(self):
+        for args in ([], ["install"], ["install", "12x"], ["remove", "620"]):
+            out = subprocess.run([sys.executable, str(ROOT / "ui" / "frame_mods.py"), *args],
+                                 capture_output=True, text=True, timeout=30)
+            self.assertEqual(out.returncode, 1, args)
+            self.assertIn("error", json.loads(out.stdout), args)
+
+
+class ModRoutes(test_server.ServerGuards):
+    """Reuses ServerGuards' server (unresolvable SSH alias); validation runs before any SSH."""
+
+    def test_mod_input_validation(self):
+        for body in ({"action": "install", "appid": "1; reboot"}, {"action": "install", "appid": ""},
+                     {"action": "delete", "appid": "1067310"}, {"appid": "1067310"}):
+            status, payload = self.post("/api/mods", body)
+            self.assertEqual(status, 400, f"{body} -> {payload}")
+
+    def test_needs_custom_header(self):
+        self.assertEqual(self.request("POST", "/api/mods", {"action": "status", "appid": "1"})[0], 403)
+
+    def test_runs_the_mods_helper_with_its_timeout(self):
+        import server
+        with mock.patch.object(server, "steam_frame", return_value={"ok": 1}) as run:
+            self.assertEqual(server.mods({"action": "install", "appid": "1067310"}), {"ok": 1})
+        run.assert_called_once_with("install", "1067310", timeout=600, script="frame_mods.py")
+
+
+for name in [n for n in dir(test_server.ServerGuards) if n.startswith("test_")]:
+    setattr(ModRoutes, name, None)
@@ -0,0 +1,532 @@
+#!/usr/bin/env python3
+"""Runs ON the Frame (piped over SSH): UEVR, a flat-to-VR mod for Unreal games.
+
+Usage: python3 - status APPID     # can UEVR run here, is it installed, is the game running
+       python3 - install APPID    # download the pinned official release into the game's prefix
+       python3 - start APPID      # launch the game if needed, inject UEVR, confirm SteamVR frames
+       python3 - uninstall APPID  # remove exactly what install (and UEVR's first run) created
+Prints one JSON object. Errors are {"error": "..."} with exit status 1.
+
+Verified 2026-09-29 on SteamOS 0.4.1 (build 20260925.6191901), Proton 11.0
+ARM64 and SteamVR 2.18.1 with Gravitas (1067310): after injection the game has
+UEVRBackend.dll loaded and SteamVR counts frame submits for it. Stereo image,
+head tracking and controls were not seen: the headset was unworn (docs/mods.md).
+
+UEVR's own injector (a .NET WPF app) is not used. Under Wine and FEX it hung
+or ignored input in about one session in four, and gamescope keeps real input
+away from it. Instead the official Windows embeddable Python runs INJECT_PY in
+the game's Wine session, doing what the injector does on Inject.
+
+Nothing here is bundled. UEVR comes from praydog's GitHub release and Python
+from python.org, each checked against a pinned hash. Files live in
+<prefix>/drive_c/frame-control, never in the game's own folder, and a receipt
+records what to remove.
+"""
+import fcntl
+import hashlib
+import json
+import os
+import re
+import shutil
+import subprocess
+import sys
+import time
+import urllib.request
+import zipfile
+from pathlib import Path
+
+HOME = Path.home()
+STEAM = HOME / ".local/share/Steam"
+CACHE = HOME / ".cache/frame-control/mods"
+RECEIPTS = HOME / ".local/share/frame-control/mods"
+LOCK = Path("/tmp/frame-control-mods.lock")  # tmpfs: gone at reboot, never left in ~
+VRCMD = "/opt/steamvr/bin/linuxarm64/vrcmd"
+MANAGED = "frame-control"  # drive_c/<this> inside the game's prefix
+
+UEVR = {"version": "1.05", "dir": "uevr-1.05",
+        "url": "https://github.com/praydog/UEVR/releases/download/1.05/UEVR.zip",
+        "sha256": "af4f2f91306802d7ee4e8497d483a547ac8e9a3067dbafb81324100524215d3c"}
+# Windows x64 embeddable Python, to run INJECT_PY. Hash from python.org's
+# release-file API (sha256_sum).
+PYTHON = {"version": "3.14.7", "dir": "python-3.14.7",
+          "url": "https://www.python.org/ftp/python/3.14.7/python-3.14.7-embed-amd64.zip",
+          "sha256": "d297e5ff019966817ad8502465176139f2d3d840fa4ed84b13bed399a6ab1f15"}
+MAX_UNPACKED = 200 << 20  # the two archives unpack to about 50 MB
+MAX_DOWNLOAD = 50 << 20  # each archive is 7–13 MB
+
+# The game's environment a second program needs to join its Wine session. Not
+# WINESERVERSOCKET and friends: those are inherited file descriptors.
+GAME_ENV = re.compile(r"(WINEPREFIX|WINEDLLPATH|WINEDLLOVERRIDES|WINEFSYNC|WINEDEBUG|PATH|DISPLAY|"
+                      r"XDG_RUNTIME_DIR|PROTON_VR_RUNTIME|FEX_APP_CONFIG|FEX_APP_CONFIG_LOCATION|"
+                      r"SteamAppId|SteamGameId|STEAM_COMPAT_DATA_PATH|WINE_LARGE_ADDRESS_AWARE)=")
+
+
+# Runs under Windows Python in the game's Wine session: the steps of UEVR
+# 1.05's frontend (UEVR/MainWindow.xaml.cs Inject_Clicked, UEVR/Injector.cs)
+# with "Nullify VR plugins" on and the OpenVR runtime. Prints one JSON line.
+INJECT_PY = r"""
+import ctypes, json, os, sys
+from ctypes import wintypes as W
+exe, uevr, profile = sys.argv[1:4]
+k32 = ctypes.WinDLL("kernel32", use_last_error=True)
+H, P, SZ = W.HANDLE, ctypes.c_void_p, ctypes.c_size_t
+for name, res, args in (
+        ("OpenProcess", H, [W.DWORD, W.BOOL, W.DWORD]),
+        ("CloseHandle", W.BOOL, [H]),
+        ("VirtualAllocEx", P, [H, P, SZ, W.DWORD, W.DWORD]),
+        ("VirtualFreeEx", W.BOOL, [H, P, SZ, W.DWORD]),
+        ("WriteProcessMemory", W.BOOL, [H, P, P, SZ, P]),
+        ("CreateRemoteThread", H, [H, P, SZ, P, P, W.DWORD, P]),
+        ("WaitForSingleObject", W.DWORD, [H, W.DWORD]),
+        ("GetModuleHandleW", W.HMODULE, [W.LPCWSTR]),
+        ("LoadLibraryW", W.HMODULE, [W.LPCWSTR]),
+        ("FreeLibrary", W.BOOL, [W.HMODULE]),
+        ("GetProcAddress", P, [W.HMODULE, ctypes.c_char_p]),
+        ("CreateToolhelp32Snapshot", H, [W.DWORD, W.DWORD]),
+        ("Process32FirstW", W.BOOL, [H, P]), ("Process32NextW", W.BOOL, [H, P]),
+        ("Module32FirstW", W.BOOL, [H, P]), ("Module32NextW", W.BOOL, [H, P])):
+    fn = getattr(k32, name)
+    fn.restype, fn.argtypes = res, args
+INVALID = ctypes.c_void_p(-1).value
+
+class Entry(ctypes.Structure):  # PROCESSENTRY32W
+    _fields_ = [("size", W.DWORD), ("usage", W.DWORD), ("pid", W.DWORD), ("heap", ctypes.c_void_p),
+                ("module", W.DWORD), ("threads", W.DWORD), ("parent", W.DWORD), ("prio", ctypes.c_long),
+                ("flags", W.DWORD), ("name", W.WCHAR * 260)]
+
+class Module(ctypes.Structure):  # MODULEENTRY32W
+    _fields_ = [("size", W.DWORD), ("mid", W.DWORD), ("pid", W.DWORD), ("glbl", W.DWORD), ("proc", W.DWORD),
+                ("base", ctypes.c_void_p), ("bytes", W.DWORD), ("handle", W.HMODULE),
+                ("name", W.WCHAR * 256), ("path", W.WCHAR * 260)]
+
+def fail(msg):
+    print(json.dumps({"error": f"{msg} (Windows error {ctypes.get_last_error()})"})); sys.exit(1)
+
+def snapshot(flags, pid, entry, first, next_, match):
+    snap = k32.CreateToolhelp32Snapshot(flags, pid)
+    if not snap or snap == INVALID:
+        fail("couldn't list processes")
+    try:
+        entry.size = ctypes.sizeof(entry)
+        ok = first(snap, ctypes.byref(entry))
+        while ok:
+            if match(entry):
+                return entry
+            ok = next_(snap, ctypes.byref(entry))
+    finally:
+        k32.CloseHandle(snap)
+
+def remote_call(proc, fn, arg, wait_ms):
+    t = k32.CreateRemoteThread(proc, None, 0, fn, arg, 0, None)
+    if not t:
+        fail("CreateRemoteThread failed")
+    try:
+        return k32.WaitForSingleObject(t, wait_ms) == 0  # WAIT_OBJECT_0
+    finally:
+        k32.CloseHandle(t)
+
+def inject(proc, pid, name):
+    path = os.path.join(uevr, name)
+    data = ctypes.create_unicode_buffer(path)
+    mem = k32.VirtualAllocEx(proc, None, ctypes.sizeof(data), 0x3000, 0x04)  # commit|reserve, read/write
+    if not mem:
+        fail(f"couldn't allocate in {exe}")
+    try:
+        if not k32.WriteProcessMemory(proc, mem, data, ctypes.sizeof(data), None):
+            fail(f"couldn't write into {exe}")
+        load = k32.GetProcAddress(k32.GetModuleHandleW("kernel32.dll"), b"LoadLibraryW")
+        if not remote_call(proc, load, mem, 30000):
+            fail(f"loading {name} into {exe} didn't finish in 30 s")
+    finally:
+        k32.VirtualFreeEx(proc, mem, 0, 0x8000)  # MEM_RELEASE
+    m = snapshot(0x18, pid, Module(), k32.Module32FirstW, k32.Module32NextW,  # TH32CS_SNAPMODULE | SNAPMODULE32
+                 lambda m: m.path.lower() == path.lower())
+    if not m:
+        fail(f"{name} didn't load into {exe}")
+    return path, m.base
+
+e = snapshot(2, 0, Entry(), k32.Process32FirstW, k32.Process32NextW,  # TH32CS_SNAPPROCESS
+             lambda e: e.name.lower() == exe.lower())
+if not e:
+    fail(f"{exe} isn't running")
+pid = e.pid
+proc = k32.OpenProcess(0x1F0FFF, False, pid)  # PROCESS_ALL_ACCESS
+if not proc:
+    fail(f"couldn't open {exe}")
+path, base = inject(proc, pid, "UEVRPluginNullifier.dll")
+local = k32.LoadLibraryW(path)
+fn = local and k32.GetProcAddress(local, b"nullify")
+if not fn:
+    fail("couldn't find UEVRPluginNullifier.dll's nullify")
+offset = fn - local  # same DLL, same layout in both processes
+k32.FreeLibrary(local)
+# The frontend waits 2 s for nullify and carries on either way; so do we, but say so.
+nullified = remote_call(proc, base + offset, None, 2000)
+inject(proc, pid, "openvr_api.dll")
+# The frontend saves the runtime choice in the per-game config before UEVRBackend reads it.
+os.makedirs(profile, exist_ok=True)
+cfg = os.path.join(profile, "config.txt")
+lines = open(cfg).read().splitlines() if os.path.exists(cfg) else []
+lines = [l for l in lines if not l.startswith("Frontend_RequestedRuntime=")] + ["Frontend_RequestedRuntime=openvr_api.dll"]
+open(cfg, "w").write("\n".join(lines) + "\n")
+inject(proc, pid, "UEVRBackend.dll")
+k32.CloseHandle(proc)
+print(json.dumps({"pid": pid, "nullified": nullified}))
+"""
+
+
+class Fail(Exception):
+    pass
+
+
+def libraries():
+    """Steam library folders: the default one plus any in libraryfolders.vdf."""
+    libs = [STEAM]
+    try:
+        text = (STEAM / "steamapps/libraryfolders.vdf").read_text(errors="replace")
+        libs += [Path(p.replace("\\\\", "\\")) for p in re.findall(r'"path"\s+"([^"]+)"', text)]
+    except OSError:
+        pass
+    seen, out = set(), []
+    for lib in libs:
+        key = os.path.realpath(lib)
+        if key not in seen:
+            seen.add(key)
+            out.append(lib)
+    return out
+
+
+def game(appid):
+    """Where the game is installed and its Proton prefix, from its app manifest."""
+    for lib in libraries():
+        manifest = lib / f"steamapps/appmanifest_{appid}.acf"
+        try:
+            text = manifest.read_text(errors="replace")
+        except OSError:
+            continue
+        m = re.search(r'"installdir"\s+"([^"]+)"', text)
+        if not m:
+            continue
+        name = re.search(r'"name"\s+"([^"]*)"', text)
+        return {"name": name.group(1) if name else str(appid),
+                "dir": lib / "steamapps/common" / m.group(1),
+                "prefix": lib / f"steamapps/compatdata/{appid}/pfx"}
+    raise Fail(f"app {appid} isn't installed on this Frame")
+
+
+def shipping_exe(game_dir):
+    """The Unreal Engine game binary (…/Binaries/Win64/*-Win64-Shipping.exe), or None."""
+    found = [p for p in game_dir.glob("*/Binaries/Win64/*.exe") if p.name.lower().endswith("-win64-shipping.exe")]
+    found += [p for p in game_dir.glob("Binaries/Win64/*.exe") if p.name.lower().endswith("-win64-shipping.exe")]
+    return max(found, key=lambda p: p.stat().st_size) if found else None
+
+
+def game_pid(exe_name):
+    """The running Wine process for this .exe (its cmdline is the Windows path)."""
+    want = "\\" + exe_name.lower()
+    for d in Path("/proc").iterdir():
+        if not d.name.isdigit():
+            continue
+        try:
+            cmd = (d / "cmdline").read_bytes().split(b"\0")[0].decode(errors="replace").lower()
+        except OSError:
+            continue
+        if cmd.endswith(want):
+            return int(d.name)
+    return None
+
+
+def loaded(pid, name):
+    try:
+        return any(line.rstrip().endswith("/" + name) for line in open(f"/proc/{pid}/maps"))
+    except OSError:
+        return False
+
+
+def receipt_path(appid):
+    return RECEIPTS / f"{appid}-uevr.json"
+
+
+def read_receipt(appid):
+    try:
+        return json.loads(receipt_path(appid).read_text())
+    except (OSError, ValueError):
+        return None
+
+
+def managed_dir(g):
+    return g["prefix"] / "drive_c" / MANAGED
+
+
+def user_dirs(g, exe):
+    """What UEVR itself writes into the prefix when it first runs."""
+    user = g["prefix"] / "drive_c/users/steamuser/AppData"
+    return {"profile": user / "Roaming/UnrealVRMod" / exe.stem,  # per-game settings and log.txt
+            "injector": user / "Local/praydog"}                  # the injector's own settings
+
+
+def status(appid):
+    g = game(appid)
+    exe = shipping_exe(g["dir"])
+    r = read_receipt(appid)
+    pid = game_pid(exe.name) if exe else None
+    return {"appid": appid, "name": g["name"], "mod": "UEVR", "version": UEVR["version"],
+            "eligible": bool(exe), "exe": exe.name if exe else None,
+            "prefix": g["prefix"].is_dir(), "installed": bool(r),
+            "running": bool(pid), "injected": bool(pid and loaded(pid, "UEVRBackend.dll"))}
+
+
+def fetch(url, digest, algo):
+    """Download into the cache once, and check its hash every time it's used."""
+    CACHE.mkdir(parents=True, exist_ok=True)
+    path = CACHE / url.rsplit("/", 1)[1]
+    if not path.exists():
+        part = path.with_suffix(path.suffix + ".part")
+        try:
+            with urllib.request.urlopen(url, timeout=60) as r, open(part, "wb") as f:
+                for block in iter(lambda: r.read(1 << 20), b""):
+                    if f.tell() + len(block) > MAX_DOWNLOAD:
+                        raise Fail(f"{url} is bigger than expected; stopped the download")
+                    f.write(block)
+        except (OSError, Fail) as e:
+            part.unlink(missing_ok=True)
+            raise Fail(f"download failed: {url}: {e}")
+        part.rename(path)
+    h = hashlib.new(algo)
+    with open(path, "rb") as f:
+        for block in iter(lambda: f.read(1 << 20), b""):
+            h.update(block)
+    if h.hexdigest() != digest:
+        path.unlink()
+        raise Fail(f"{path.name} doesn't match its published {algo}; deleted it, try again")
+    return path
+
+
+def unpack(archive, dest, budget):
+    """Extract a ZIP into dest, refusing anything that would land outside it."""
+    root = os.path.realpath(dest)
+    with zipfile.ZipFile(archive) as z:
+        for info in z.infolist():
+            target = os.path.realpath(os.path.join(dest, info.filename))
+            if target != root and not target.startswith(root + os.sep):
+                raise Fail(f"{archive.name} has an entry outside its folder: {info.filename}")
+            if (info.external_attr >> 16) & 0o170000 == 0o120000:
+                raise Fail(f"{archive.name} contains a symlink: {info.filename}")
+            budget -= info.file_size
+            if budget < 0:
+                raise Fail(f"{archive.name} unpacks to more than expected")
+        z.extractall(dest)
+    return budget
+
+
+def install(appid):
+    g = game(appid)
+    exe = shipping_exe(g["dir"])
+    if not exe:
+        raise Fail(f"{g['name']} doesn't look like an Unreal Engine game (no *-Win64-Shipping.exe), so UEVR can't hook it")
+    if not g["prefix"].is_dir():
+        raise Fail(f"{g['name']} has no Proton prefix yet; play it once, then add the mod")
+    if game_pid(exe.name):
+        raise Fail(f"{g['name']} is running; quit it first")
+    if read_receipt(appid):
+        return {"message": f"UEVR {UEVR['version']} is already installed for {g['name']}", **status(appid)}
+    archives = [(fetch(UEVR["url"], UEVR["sha256"], "sha256"), UEVR["dir"])]
+    archives.append((fetch(PYTHON["url"], PYTHON["sha256"], "sha256"), PYTHON["dir"]))
+    base = managed_dir(g)
+    dirs = user_dirs(g, exe)
+    fresh = [str(d) for d in (dirs["profile"].parent, base) if not d.exists()]  # remove on uninstall if empty
+    stage = base / f".staging-{os.getpid()}"
+    shutil.rmtree(stage, ignore_errors=True)
+    try:
+        budget = MAX_UNPACKED
+        for archive, sub in archives:
+            budget = unpack(archive, stage / sub, budget)
+        for need in (stage / UEVR["dir"] / "UEVRBackend.dll", stage / PYTHON["dir"] / "python.exe"):
+            if not need.is_file():
+                raise Fail(f"the download has no {need.name}")
+        if game_pid(exe.name):  # it may have started during the download
+            raise Fail(f"{g['name']} started; quit it first")
+        (stage / PYTHON["dir"] / "frame_inject.py").write_text(INJECT_PY)
+        for sub in (UEVR["dir"], PYTHON["dir"]):
+            shutil.rmtree(base / sub, ignore_errors=True)
+            (stage / sub).rename(base / sub)
+    finally:
+        shutil.rmtree(stage, ignore_errors=True)
+        if str(base) in fresh:
+            try:
+                base.rmdir()  # only succeeds if the install failed and left it empty
+            except OSError:
+                pass
+    receipt = {"appid": appid, "mod": "UEVR", "version": UEVR["version"], "exe": exe.name,
+               "installed": int(time.time()), "prefix": str(g["prefix"]),
+               "remove": [str(base / UEVR["dir"]), str(base / PYTHON["dir"])],
+               # Parents that didn't exist yet (UEVR makes UnrealVRMod), deepest first.
+               "remove_if_empty": fresh,
+               # UEVR creates these on first injection. Remove them on uninstall
+               # only if they weren't there before, so earlier settings survive.
+               "remove_if_created": {k: str(v) for k, v in dirs.items() if not v.exists()},
+               "sources": [UEVR["url"], PYTHON["url"]]}
+    RECEIPTS.mkdir(parents=True, exist_ok=True)
+    tmp = receipt_path(appid).with_suffix(".tmp")
+    tmp.write_text(json.dumps(receipt, indent=1))
+    tmp.rename(receipt_path(appid))
+    return {"message": f"Installed UEVR {UEVR['version']} for {g['name']}", **status(appid)}
+
+
+def x11_windows(display):
+    """(id, name, width) for each named top-level window, via xwininfo."""
+    try:
+        out = subprocess.run(["xwininfo", "-root", "-tree"], env={**os.environ, "DISPLAY": display},
+                             capture_output=True, text=True, timeout=10).stdout
+    except (OSError, subprocess.TimeoutExpired):
+        return []
+    return [(int(m[1], 16), m[2], int(m[3])) for m in re.finditer(r'(0x[0-9a-f]+) "([^"]*)":.*?\)\s+(\d+)x\d+', out)]
+
+
+def frame_submits(appid):
+    """SteamVR's count of frames the app has submitted, or None if it isn't a scene app."""
+    try:
+        stats = json.loads(subprocess.run([VRCMD, "--stats"], capture_output=True, text=True, timeout=15).stdout)
+    except (OSError, ValueError, subprocess.TimeoutExpired):
+        return None
+    if not isinstance(stats, list):
+        return None
+    return next((s.get("frame_submits") for s in stats if isinstance(s, dict) and s.get("key") == f"steam.app.{appid}"), None)
+
+
+def wait(what, seconds, check, step=2):
+    end = time.time() + seconds
+    while time.time() < end:
+        v = check()
+        if v is not None and v is not False:  # 0 frames is still an answer
+            return v
+        time.sleep(step)
+    raise Fail(f"timed out waiting for {what}")
+
+
+def start(appid):
+    g = game(appid)
+    r = read_receipt(appid)
+    if not r:
+        raise Fail(f"UEVR isn't installed for {g['name']}")
+    exe = r["exe"]
+    pid = game_pid(exe)
+    if pid and loaded(pid, "UEVRBackend.dll"):
+        return {"message": f"UEVR is already running in {g['name']}", "frame_submits": frame_submits(appid), **status(appid)}
+    if not pid:
+        subprocess.Popen(["steam", f"steam://rungameid/{appid}"], stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL,
+                         env={**os.environ, "DISPLAY": os.environ.get("DISPLAY", ":0")}, start_new_session=True)
+        pid = wait(f"{g['name']} to start", 120, lambda: game_pid(exe))
+    try:
+        environ = Path(f"/proc/{pid}/environ").read_text(errors="replace")
+    except OSError:
+        raise Fail(f"{exe} exited") from None
+    game_env = dict(line.split("=", 1) for line in environ.split("\0") if GAME_ENV.match(line))
+    display = game_env.get("DISPLAY")
+    if not display or "WINEPREFIX" not in game_env:
+        raise Fail(f"{exe} doesn't look like a Proton game process")
+    # UEVR hooks the game's D3D11/12 device, so wait for its window. Proton's
+    # own helper windows ("Steam", "Default IME", …) are small.
+    wait("the game window", 90, lambda: any(w[2] >= 640 for w in x11_windows(display)))
+    time.sleep(10)
+    # Our own environment (HOME and the rest) under the game's Wine settings.
+    env = {**os.environ, **game_env}
+    base = f"C:\\{MANAGED}"
+    profile = f"C:\\users\\steamuser\\AppData\\Roaming\\UnrealVRMod\\{Path(exe).stem}"
+    try:
+        out = subprocess.run(["wine", f"{base}\\{PYTHON['dir']}\\python.exe", f"{base}\\{PYTHON['dir']}\\frame_inject.py",
+                              exe, f"{base}\\{UEVR['dir']}", profile], env=env, capture_output=True, text=True,
+                             timeout=120, stdin=subprocess.DEVNULL,
+                             cwd=str(Path(r["prefix"]) / "drive_c" / MANAGED))
+    except subprocess.TimeoutExpired:
+        raise Fail("the injection step didn't finish in 2 minutes") from None
+    reply = None
+    for line in reversed(out.stdout.splitlines()):
+        try:
+            reply = json.loads(line)
+            break
+        except ValueError:
+            continue
+    if not isinstance(reply, dict):
+        reply = None
+    if not reply or "error" in reply:
+        raise Fail("UEVR injection failed: " + (reply or {}).get("error", (out.stderr.strip().splitlines() or ["no output"])[-1]))
+    try:
+        wait("UEVRBackend.dll to load in the game", 20, lambda: loaded(pid, "UEVRBackend.dll"))
+    except Fail:
+        raise Fail(f"the injection reported success but {exe} has no UEVRBackend.dll") from None
+    submits = None
+    try:
+        submits = wait("SteamVR frames", 30, lambda: frame_submits(appid))
+    except Fail:
+        pass
+    return {"message": f"UEVR injected into {g['name']}" + ("; SteamVR is receiving its frames" if submits is not None
+                                                            else "; SteamVR hasn't reported frames from it yet"),
+            "frame_submits": submits, **status(appid)}
+
+
+def uninstall(appid):
+    r = read_receipt(appid)
+    if not r:
+        raise Fail(f"UEVR isn't installed for app {appid}")
+    if game_pid(r["exe"]):
+        raise Fail("the game is running; quit it first")
+    prefix = os.path.realpath(r["prefix"])
+    if not prefix.endswith(f"/steamapps/compatdata/{appid}/pfx"):
+        raise Fail(f"receipt names a prefix that isn't app {appid}'s: {r['prefix']}")
+    # Only ever our folder and UEVR's own settings folders for this game, even
+    # if the receipt says otherwise.
+    managed = os.path.join(prefix, "drive_c", MANAGED)
+    uevr_dirs = {os.path.realpath(str(d)) for d in user_dirs({"prefix": Path(prefix)}, Path(r["exe"])).values()}
+    targets = list(r.get("remove", [])) + list(r.get("remove_if_created", {}).values())
+    for t in targets:
+        real = os.path.realpath(t)
+        if not (real.startswith(managed + os.sep) or real in uevr_dirs):
+            raise Fail(f"receipt lists a path Frame Control didn't create: {t}")
+    for t in targets:
+        shutil.rmtree(t, ignore_errors=True)
+    left = [t for t in targets if os.path.lexists(t)]
+    if left:  # keep the receipt, so Remove can be tried again
+        raise Fail("couldn't remove " + ", ".join(left))
+    parents = {os.path.realpath(os.path.join(prefix, "drive_c/users/steamuser/AppData/Roaming/UnrealVRMod")), managed}
+    for t in r.get("remove_if_empty", []):
+        if os.path.realpath(t) in parents:
+            try:
+                os.rmdir(t)
+            except OSError:
+                pass  # something else lives there now
+    receipt_path(appid).unlink()
+    if not any(RECEIPTS.glob("*-uevr.json")):  # no other game uses the downloads
+        shutil.rmtree(CACHE, ignore_errors=True)
+        try:
+            RECEIPTS.rmdir()
+        except OSError:
+            pass
+    return {"message": "Removed UEVR", "appid": appid, "removed": targets}
+
+
+def main(argv):
+    if len(argv) != 2 or argv[0] not in ("status", "install", "start", "uninstall") or not argv[1].isdigit():
+        raise Fail("usage: status|install|start|uninstall APPID")
+    action = {"status": status, "install": install, "start": start, "uninstall": uninstall}[argv[0]]
+    if action is status:
+        return status(int(argv[1]))
+    # One change at a time, or an uninstall could delete what an install is moving in.
+    LOCK.parent.mkdir(parents=True, exist_ok=True)
+    with open(LOCK, "w") as lock:
+        try:
+            fcntl.flock(lock, fcntl.LOCK_EX | fcntl.LOCK_NB)
+        except OSError:
+            raise Fail("another mod action is still running on the Frame; try again when it finishes") from None
+        return action(int(argv[1]))
+
+
+if __name__ == "__main__":
+    try:
+        print(json.dumps(main(sys.argv[1:])))
+    except Fail as e:
+        print(json.dumps({"error": str(e)}))
+        sys.exit(1)
+    except Exception as e:  # still one JSON object, for the server to show
+        print(json.dumps({"error": f"{type(e).__name__}: {e}"}))
+        sys.exit(1)
@@ -331,9 +331,9 @@
  .and-grid { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 2fr); gap: 22px; align-items: start; }
  .and-col { display: grid; gap: 22px; align-content: start; }
  .rep-item .s { white-space: normal; }
-  #bugDlg, #repDlg, #titleDlg, #wiDlg, #pwDlg, #apkAltDlg, #aboutDlg { background: #1e2329; color: var(--text); border: 1px solid rgba(255,255,255,.1); border-radius: 4px;
+  #bugDlg, #repDlg, #titleDlg, #wiDlg, #pwDlg, #apkAltDlg, #aboutDlg, #modDlg { background: #1e2329; color: var(--text); border: 1px solid rgba(255,255,255,.1); border-radius: 4px;
            padding: 22px; width: min(560px, 92vw); box-shadow: 0 20px 60px rgba(0,0,0,.6); }
-  #bugDlg::backdrop, #repDlg::backdrop, #titleDlg::backdrop, #wiDlg::backdrop, #pwDlg::backdrop, #apkAltDlg::backdrop, #aboutDlg::backdrop { background: rgba(0,0,0,.55); }
+  #bugDlg::backdrop, #repDlg::backdrop, #titleDlg::backdrop, #wiDlg::backdrop, #pwDlg::backdrop, #apkAltDlg::backdrop, #aboutDlg::backdrop, #modDlg::backdrop { background: rgba(0,0,0,.55); }
  #bugDlg { width: min(640px, calc(100vw - 40px)); }
  #bugForm label.field { display: block; font-size: 12.5px; color: var(--muted); margin-top: 10px; }
  #bugForm label.field input, #bugForm label.field textarea, #bugForm select { margin-top: 5px; }
@@ -342,7 +342,7 @@
  #bugForm .popt { margin: 14px 0 0; }
  #bugForm .sentlog { max-height: 200px; }
  #bugWarn { color: var(--muted); font-size: 12.5px; line-height: 1.45; margin: 12px 0 0; }
-  #bugDlg h2, #repDlg h2, #titleDlg h2, #wiDlg h2, #pwDlg h2, #apkAltDlg h2, #aboutDlg h2 { margin: 0 0 14px; font-size: 15px; letter-spacing: 1.5px; text-transform: uppercase; color: var(--bright); }
+  #bugDlg h2, #repDlg h2, #titleDlg h2, #wiDlg h2, #pwDlg h2, #apkAltDlg h2, #aboutDlg h2, #modDlg h2 { margin: 0 0 14px; font-size: 15px; letter-spacing: 1.5px; text-transform: uppercase; color: var(--bright); }
  .about-text { max-height: 55vh; overflow: auto; }
  .about-text pre { white-space: pre-wrap; font-size: 12px; color: var(--muted); }
  .about-text summary { cursor: pointer; margin: 8px 0; }
@@ -1187,6 +1187,21 @@
  <div class="actions"><button id="apkAltClose">Close</button></div>
 </dialog>

+<dialog id="modDlg" aria-labelledby="modTitle">
+  <h2 id="modTitle">Play in VR with UEVR</h2>
+  <p id="modState" class="sub"></p>
+  <p class="sub">UEVR by praydog turns many Unreal Engine games into VR games. Frame Control downloads
+    the official UEVR 1.05 release and python.org's Windows Python, which it uses to load UEVR into the game
+    (about 20 MB), checks their hashes, and keeps them in this game's Proton prefix, not the game's folder.
+    Remove takes them out again.</p>
+  <p class="sub">Tested on the Frame with one game so far. Whether a game looks and plays right in VR varies;
+    UEVR's own menu in the headset has the per-game settings.</p>
+  <div class="row rep-actions"><span class="sub" id="modMsg"></span><span class="spacer"></span>
+    <button type="button" class="small" id="modClose">Close</button>
+    <button type="button" class="small" id="modRemove" hidden>Remove UEVR</button>
+    <button type="button" class="action small" id="modInstall" hidden>Install UEVR</button>
+    <button type="button" class="play small" id="modStart" hidden>▶ PLAY IN VR</button></div>
+</dialog>
 <dialog id="aboutDlg" aria-labelledby="aboutTitle">
  <h2 id="aboutTitle">About and licences</h2>
  <p>Frame Control is MIT-licensed. It ships other people's software, each under its own licence: the notices and
@@ -2962,7 +2977,8 @@ function gameButtons(id, name, free) {
  const open = `<button class="small" data-gm="store" data-id="${id}" data-name="${esc(name)}" title="Open the store page in the headset">Store on Frame</button>`;
  if (d && d.appid === id) return `<span class="tag">${d.paused ? "Paused" : "Downloading"} ${d.percent ?? 0}%</span>`;
  if (g && g.installed) return `<span class="tag">Installed</span>` +
-    `<button class="play small" data-launch="${id}" data-name="${esc(name)}">▶ PLAY</button>`;
+    `<button class="play small" data-launch="${id}" data-name="${esc(name)}">▶ PLAY</button>` +
+    `<button class="small" data-mod="${id}" data-name="${esc(name)}" title="Flat-to-VR mod for Unreal Engine games">VR mod</button>`;
  if (g) return `<button class="action small" data-gm="install" data-id="${id}" data-name="${esc(name)}">Install on Frame</button>`;
  return `<a href="${storeUrl}" target="_blank" rel="noopener" title="Opens in your browser">${free ? "Get" : "Buy"} on Steam ↗</a>${open}`;
 }
@@ -3034,6 +3050,45 @@ document.body.addEventListener("click", async e => {
 });
 loadOwned();

+// ---- VR mod (UEVR) for one installed game; frame_mods.py does the work ----
+const mod = { appid: null, name: "" };
+function showMod(st, note) {
+  const busy = note === null;
+  $("modTitle").textContent = `${mod.name} in VR`;
+  $("modState").textContent = !st ? "Checking the game on the Frame…"
+    : !st.eligible ? "This doesn't look like an Unreal Engine game, so UEVR can't run it."
+    : !st.prefix ? "Play the game once first, so Steam sets up its Proton prefix."
+    : st.injected ? "UEVR is running in the game now. Put on the headset."
+    : st.installed ? `UEVR ${st.version} is installed for this game.${st.running ? " The game is running; Play in VR adds UEVR to it." : ""}`
+    : `UEVR ${st.version} isn't installed for this game yet.`;
+  $("modMsg").textContent = busy ? "Working… this can take a few minutes" : note || "";
+  const ok = st && st.eligible && st.prefix;
+  $("modInstall").hidden = !ok || st.installed; $("modStart").hidden = !ok || !st.installed || st.injected;
+  $("modRemove").hidden = !st || !st.installed;
+  for (const b of ["modInstall", "modStart", "modRemove"]) $(b).disabled = busy || (b === "modRemove" && st && st.running);
+}
+async function modAction(action, label) {
+  const appid = mod.appid;
+  showMod(mod.st, null);
+  const res = await act(`${label} for ${mod.name}`, () => api("/api/mods", { action, appid }));
+  if (appid !== mod.appid) return;
+  try { mod.st = await api("/api/mods", { action: "status", appid }); } catch {}
+  showMod(mod.st, res ? res.message : "Didn't work; the log has the reason");
+}
+document.body.addEventListener("click", async e => {
+  const b = e.target.closest("[data-mod]"); if (!b) return;
+  mod.appid = b.dataset.mod; mod.name = b.dataset.name; mod.st = null;
+  showMod(null, "");
+  $("modDlg").showModal();
+  const appid = mod.appid;
+  try { const st = await api("/api/mods", { action: "status", appid }); if (appid === mod.appid) { mod.st = st; showMod(st, ""); } }
+  catch (err) { if (appid === mod.appid) $("modState").textContent = err.message; }
+});
+$("modInstall").onclick = () => modAction("install", "Install UEVR");
+$("modStart").onclick = () => modAction("start", "Start UEVR");
+$("modRemove").onclick = () => modAction("uninstall", "Remove UEVR");
+$("modClose").onclick = () => $("modDlg").close();
+
 // ---- Discover apps ----
 const sourceState = { vr: null, installable: false, source: "", apps: [], sources: [], request: 0, detail: null, detailRequest: 0, jobs: new Map() };
 const storeName = s => String(s || "").replace(/ \(demo\)$/i, "");
@@ -572,13 +572,14 @@ def launch(body):
    return {"message": f"Launching {appid}"}


-def steam_frame(*args, timeout=40):
-    """Run frame_steam.py on the Frame (it drives the Steam client) and return its JSON."""
+def steam_frame(*args, timeout=40, script="frame_steam.py"):
+    """Run frame_steam.py (it drives the Steam client), or another on-Frame
+    helper with the same JSON contract, on the Frame and return its JSON."""
    try:
        out = ssh("python3 - " + " ".join(map(shlex.quote, args)),
-                  stdin=(HERE / "frame_steam.py").read_text(), timeout=timeout)
+                  stdin=(HERE / script).read_text(), timeout=timeout)
    except Failure as e:
-        # frame_steam.py prints {"error": ...} on stdout when it fails, but ssh()
+        # The helper prints {"error": ...} on stdout when it fails, but ssh()
        # reports stderr instead if there was any, so look in both.
        for line in [*reversed(getattr(e, "stdout", "").splitlines()), *reversed(str(e).splitlines())]:
            try:
@@ -629,6 +630,20 @@ def vr(body):
    return result


+# Downloads are about 20 MB; starting waits for the game, the injection and SteamVR.
+MOD_TIMEOUT = {"status": 40, "install": 600, "start": 900, "uninstall": 60}
+
+
+def mods(body):
+    """UEVR for one installed Unreal game: status, install, start (inject) or uninstall."""
+    appid, action = str(body.get("appid", "")), body.get("action")
+    if not APPID.match(appid):
+        raise Failure("bad appid", 400)
+    if action not in MOD_TIMEOUT:
+        raise Failure("action must be " + ", ".join(MOD_TIMEOUT), 400)
+    return steam_frame(action, appid, timeout=MOD_TIMEOUT[action], script="frame_mods.py")
+
+
 def steam_search(query):
    q = parse_qs(query)
    cc = (q.get("cc") or [""])[0].upper()
@@ -2146,7 +2161,7 @@ POST = {
    "/api/agent/approval": agent_approval, "/api/assistant/chat": assistant_chat,
    "/api/input": remote_input, "/api/touch": remote_touch,
    "/api/settings/artwork": frame_steamgriddb.save_settings,
-    "/api/sources": source_manage, "/api/sources/install": source_install, "/api/android/display": android_display, "/api/android": android, "/api/titles": titles, "/api/launch": launch, "/api/steam": steam, "/api/volume": set_volume, "/api/clipboard": clipboard,
+    "/api/sources": source_manage, "/api/sources/install": source_install, "/api/android/display": android_display, "/api/android": android, "/api/titles": titles, "/api/launch": launch, "/api/steam": steam, "/api/mods": mods, "/api/volume": set_volume, "/api/clipboard": clipboard,
        "/api/flatpak": flatpak, "/api/open": open_thing, "/api/shots/save": save_shots,
        "/api/webinstall/check": webinstall_check, "/api/webinstall/start": webinstall_start,
        "/api/webinstall/cancel": webinstall_cancel,
Author	SHA1	Message	Date
saphid	daf30515b1	Merge main into flat2vr-mods # Conflicts: # README.md # ui/index.html # ui/server.py	2026-09-29 13:07:33 +10:00
saphidandClaude Opus 5.5	2f056dbcff	UEVR: address the second review; recheck on the Frame frame_inject.py declares every Win32 signature, checks each result, frees its remote buffers and closes handles. Uninstall only accepts our folder and UEVR's own per-game settings folders, and keeps the receipt if anything can't be removed. The injector's reply is parsed defensively. Rechecked on a real Frame: install, three cold starts injected (33-35 s), clean uninstall. Part of #26. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>	2026-09-29 13:04:12 +10:00
saphidandClaude Opus 5.5	e3176a2de8	UEVR: inject with Frame Control's own script instead of UEVR's GUI injector UEVR's .NET injector, driven with XSendEvent, injected in only 6 of 8 cold starts on the Frame: in bad sessions every new injector ignored input or never showed a window. start() now runs frame_inject.py under python.org's embeddable Python (pinned SHA-256) in the game's Wine session, repeating the frontend's own Inject steps: nullify VR plugins, load openvr_api.dll, set Frontend_RequestedRuntime, load UEVRBackend.dll. Verified 9/9 cold starts in 33-35 s and a clean UI install/play/remove cycle. No .NET download any more (47 MB installed instead of about 190 MB). Also from the SWE-2 Max review: one mod action at a time (flock), a download size cap, errors always reported as JSON, a receipt can't name another app's prefix, 0 frames counts as an answer, and a longer server timeout for start. Part of #26. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>	2026-09-29 12:53:28 +10:00
saphidandClaude Opus 5.5	416f3181cc	Add a UEVR mod manager: install, play in VR and remove from Frame Control Installed Unreal Engine games get a "VR mod" button. ui/frame_mods.py runs on the Frame: it downloads the pinned official UEVR 1.05 release and Microsoft's .NET 6 runtimes (hash-checked, safely unpacked) into the game's Proton prefix with a receipt; starts the game, runs the injector in the game's own Wine session and presses OpenVR + Inject with XSendEvent (gamescope keeps real input on the game); confirms UEVRBackend.dll is loaded and SteamVR counts frames; and removes exactly what it added. Verified on a real Frame 2026-09-29 with Gravitas, through the UI: install, four injections (three from a cold start), remove back to the pre-install prefix listing. The headset was unworn, so the VR image, tracking and controls are not verified. Part of #26. Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>	2026-09-29 11:52:02 +10:00