fix(desktop): strip Wayland env vars so launched apps stay on the lab display

docs/releases/UNRELEASED.md

@@ -6,7 +6,10 @@ then reset this file.
 
 ## User-facing changes
 
-- None yet.
+- `desktop_launch` now points `WAYLAND_DISPLAY` at a non-existent socket (and
+  strips `WAYLAND_SOCKET`), so GTK/Qt/Electron/Flutter apps always fall back
+  to X11 and render inside the isolated lab display instead of opening on the
+  user's real Wayland desktop (where driving them moved the real cursor).
 
 ## Internal/release changes
 
@@ -16,7 +19,9 @@ then reset this file.
 
 ### Tested
 
-- None yet.
+- Regression test asserting launched apps get `DISPLAY=<lab display>` with
+  Wayland variables unset; full desktop-linux integration suite (Xvfb +
+  xdotool + xterm) passes.
 
 ### Not tested yet
 

packages/desktop-linux/src/apps.ts

@@ -38,7 +38,17 @@ export async function launchApp(opts: LaunchAppOptions): Promise<AppHandle> {
   const daemon = await startDaemon(opts.command, opts.args ?? [], {
     logDir: opts.logDir,
     cwd: opts.cwd,
-    env: { ...opts.env, DISPLAY: opts.display },
+    env: {
+      ...opts.env,
+      DISPLAY: opts.display,
+      // Toolkits (GTK, Qt, Electron, Flutter) try Wayland first, which would
+      // open the app on the user's real desktop instead of the isolated lab
+      // display. Merely unsetting WAYLAND_DISPLAY is not enough: libwayland
+      // then falls back to the default "wayland-0" socket, so point it at a
+      // socket that cannot exist to force the X11 fallback.
+      WAYLAND_DISPLAY: "picklab-no-wayland",
+      WAYLAND_SOCKET: undefined,
+    },
   });
   const graceDeadline = Date.now() + LAUNCH_GRACE_MS;
   while (Date.now() < graceDeadline) {

packages/desktop-linux/test/integration.test.ts

@@ -167,6 +167,34 @@ describe("screenshot output validation", () => {
   });
 });
 
+describe("launchApp display isolation", () => {
+  it("redirects Wayland variables so apps render on the lab display", async () => {
+    const outFile = path.join(tmpRoot, "env-capture.txt");
+    const binDir = path.join(tmpRoot, "env-capture-bin");
+    writeExecutable(
+      path.join(binDir, "capture-env"),
+      "#!/bin/sh\n" +
+        "printf 'DISPLAY=%s\\nWAYLAND_DISPLAY=%s\\n' " +
+        '"$DISPLAY" "${WAYLAND_DISPLAY-unset}" > ' +
+        `'${outFile}'\n` +
+        "sleep 5\n",
+    );
+    const app = await launchApp({
+      display: DEAD_DISPLAY,
+      command: path.join(binDir, "capture-env"),
+      env: { ...process.env, WAYLAND_DISPLAY: "wayland-1" },
+      logDir: path.join(tmpRoot, "env-capture-logs"),
+    });
+    try {
+      const captured = fs.readFileSync(outFile, "utf8");
+      expect(captured).toContain(`DISPLAY=${DEAD_DISPLAY}`);
+      expect(captured).toContain("WAYLAND_DISPLAY=picklab-no-wayland");
+    } finally {
+      await stopPid(app.pid);
+    }
+  });
+});
+
 describe("launchApp early exit", () => {
   it("rejects with the log path when the command exits immediately", async () => {
     await expect(