fix(desktop): do not attach to dev API server on port 3847

Release builds were reusing any healthy :3847 listener (e.g. npm run
dev:desktop), which serves API only and shows "Cannot GET /". Spawn the
bundled server exclusively and error when the port is already taken.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: heqikai

README.md

@@ -255,7 +255,7 @@ Then open again, or right-click the app → **Open** the first time. (Baidu Netd
 
 **Install (Windows):** run the setup `.exe` and follow the wizard.
 
-Requires **git** on `PATH` on both platforms.
+Requires **git** on `PATH` on both platforms. **Do not run `npm run dev:desktop` while using the installed app** — both use port 3847; the dev server is API-only and causes a blank `Cannot GET /` page.
 
 **Runtime data:** `~/Library/Application Support/CodeDelta` (macOS) · `%APPDATA%\CodeDelta` (Windows)
 

apps/desktop/src-tauri/src/server.rs

@@ -140,19 +140,24 @@ fn wait_for_health(timeout: Duration) -> bool {
 }
 
 pub fn start(app: &AppHandle) -> Result<(), String> {
-    if health_ok() {
-        return Ok(());
-    }
-
     if cfg!(debug_assertions) {
-        if wait_for_health(Duration::from_secs(90)) {
+        if health_ok() {
             return Ok(());
         }
         return Err(
             "CodeDelta API is not running on port 3847. Start it with `npm run dev:codedelta` or use `npm run dev:desktop` from the repo root.".into(),
         );
     }
 
+    // Production must spawn the bundled server. Do not attach to a dev API on :3847
+    // (e.g. `npm run dev:desktop`) — it serves API only and shows "Cannot GET /".
+    if health_ok() {
+        let hint = port_in_use_hint().unwrap_or_default();
+        return Err(format!(
+            "Port {API_PORT} is already in use. Quit `npm run dev:desktop` or any other CodeDelta/dev server, then reopen the app.\n{hint}"
+        ));
+    }
+
     let mut child = spawn_bundled(app)?;
     if wait_for_health(Duration::from_secs(45)) {
         let mut guard = SERVER_CHILD.lock().map_err(|e| e.to_string())?;

packages/codedelta-server/src/index.ts

@@ -29,8 +29,14 @@ export function resolveCacheRoot(): string | undefined {
   if (env) {
     return path.isAbsolute(env) ? env : path.resolve(process.cwd(), env);
   }
-  if (process.env.CODEDELTA_DESKTOP === '1' && process.platform === 'darwin') {
-    return path.join(os.homedir(), 'Library', 'Application Support', 'CodeDelta');
+  if (process.env.CODEDELTA_DESKTOP === '1') {
+    const base =
+      process.platform === 'darwin'
+        ? path.join(os.homedir(), 'Library', 'Application Support', 'CodeDelta')
+        : process.env.APPDATA
+          ? path.join(process.env.APPDATA, 'CodeDelta')
+          : path.join(os.homedir(), '.codedelta');
+    return base;
   }
   return undefined;
 }
@@ -50,6 +56,7 @@ export function createApp(options: CreateAppOptions = {}) {
       status: 'ok',
       product: 'CodeDelta',
       gitAvailable,
+      servesUi: Boolean(options.staticRoot),
     });
   });