diff --git a/desktop/README.md b/desktop/README.md
index 29d7946..59576d1 100644
--- a/desktop/README.md
+++ b/desktop/README.md
@@ -82,7 +82,8 @@ updates without elevation.
 and checks that the bundled SPA loads over `app://j621`: the SPA fallback, an
 asset fetch, `localStorage`, OPFS, WebCodecs and the preload bridge. It exits
 non-zero on failure. With `J621_UPDATE_URL` set it also checks that the feed
-reports the expected version.
+reports the expected version. Pointing `J621_DEV_SERVER` at the Vite dev
+server checks the development path instead of the bundled one.
 
 ## Backend CORS
 
diff --git a/desktop/src/main.ts b/desktop/src/main.ts
index efaeb65..a8bea2c 100644
--- a/desktop/src/main.ts
+++ b/desktop/src/main.ts
@@ -444,12 +444,14 @@ function runSmokeTest(win: BrowserWindow): void {
         })()`, true)) as Record<string, unknown>;
 
         const expected: Record<string, unknown> = {
-          origin: APP_ORIGIN,
+          // In dev the window hosts the Vite dev server, which has no /setup
+          // screen (the SPA only asks for a backend in production builds).
+          origin: DEV_SERVER || APP_ORIGIN,
           title: "J621",
           assetOk: true,
           routeOk: true,
           mounted: true,
-          setupOk: true,
+          setupOk: !DEV_SERVER,
           storageOk: true,
           historyOk: true,
           opfsOk: true,