fix(desktop): WebKitGTK fast-path on hybrid GPUs, + compile the Tauri crate in CI

.github/dependabot.yml

@@ -6,6 +6,20 @@ updates:
       interval: weekly
     open-pull-requests-limit: 5
     groups:
+      # `next` and `eslint-config-next` ship as a matched pair, and eslint's
+      # major is load-bearing for that config - but next is a PRODUCTION
+      # dependency while the other two are DEVELOPMENT ones, so the split below
+      # proposes them in separate pull requests. Neither can pass alone:
+      # eslint-config-next 16 pulls eslint 10 and expects next 16, while eslint
+      # 10 removed the eslintrc API that `next lint` from next 15 still calls.
+      # PR #161 landed exactly that half-upgrade and left lint unrunnable until
+      # it was pinned back. Dependabot assigns a dependency to the first group
+      # it matches, so listing these first keeps them moving together.
+      nextjs-toolchain:
+        patterns:
+          - "next"
+          - "eslint"
+          - "eslint-config-next"
       production:
         dependency-type: production
       development:

.github/workflows/ci.yml

@@ -41,6 +41,33 @@ jobs:
       # Keep the standalone SDK compiling (it's excluded from the app tsconfig).
       - run: npx tsc --noEmit -p sdk/tsconfig.json
 
+  desktop:
+    name: Desktop (cargo check)
+    runs-on: ubuntu-latest
+    # The Tauri backend is the one part of this repo that nothing compiles until
+    # a release is cut: release.yml builds it, but only on a `v*` tag. So a Rust
+    # change can sit on main for weeks and first break at the moment you try to
+    # ship installers. `cargo check` is the cheap half of that build - it type-
+    # checks and borrow-checks without linking or bundling - so it catches the
+    # error where it is still a one-line fix.
+    steps:
+      - uses: actions/checkout@v7
+      - uses: dtolnay/rust-toolchain@stable
+      - uses: Swatinem/rust-cache@v2
+        with:
+          workspaces: desktop/src-tauri
+      # tauri's build script links against the system webview; without these the
+      # crate fails to configure and the check never reaches our code.
+      - name: System deps for the webview
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y --no-install-recommends \
+            libwebkit2gtk-4.1-dev libsoup-3.0-dev librsvg2-dev \
+            libjavascriptcoregtk-4.1-dev build-essential pkg-config
+      - name: cargo check
+        working-directory: desktop/src-tauri
+        run: cargo check --locked --all-targets
+
   e2e:
     name: E2E (Playwright)
     runs-on: ubuntu-latest

desktop/src-tauri/src/main.rs

@@ -371,7 +371,31 @@ fn notify(app: AppHandle, title: String, body: String) -> Result<(), String> {
         .map_err(|e| e.to_string())
 }
 
+/// Work around WebKitGTK's DMA-BUF renderer on hybrid-GPU Linux boxes.
+///
+/// WebKitGTK hands rendered frames to the compositor as DMA-BUFs. On a machine
+/// with two DRM devices - an Intel iGPU driving `modesetting` alongside a
+/// discrete NVIDIA card, which is the ordinary desktop-with-a-GPU arrangement -
+/// that import fails and WebKit drops to a fallback path instead of reporting
+/// an error. The window still draws, so it reads as "the app is slow" rather
+/// than as a bug. Measured on an idle 3840x2160 window (RTX 5060 Ti + HD 530,
+/// X11, WebKitGTK 2.52.3): 2.7-14.3% CPU in the web process with the renderer
+/// enabled, 0.0% with it disabled.
+///
+/// Only set when the operator has not expressed a preference, so anyone whose
+/// setup handles DMA-BUF correctly can opt back in with
+/// `WEBKIT_DISABLE_DMABUF_RENDERER=0`. Must run before the webview initialises.
+#[cfg(target_os = "linux")]
+fn disable_dmabuf_renderer_by_default() {
+    if std::env::var_os("WEBKIT_DISABLE_DMABUF_RENDERER").is_none() {
+        std::env::set_var("WEBKIT_DISABLE_DMABUF_RENDERER", "1");
+    }
+}
+
 fn main() {
+    #[cfg(target_os = "linux")]
+    disable_dmabuf_renderer_by_default();
+
     tauri::Builder::default()
         .plugin(tauri_plugin_notification::init())
         .invoke_handler(tauri::generate_handler![