Fix: interrupt restart fiber in start() before clearing reference

The start function was clearing the restartFiber reference without
interrupting any currently scheduled restart fiber, orphaning it.
Use the existing cancelRestart helper which properly interrupts the
fiber before clearing the reference.

Author: cursoragent

apps/desktop/src/desktopBackendManager.ts

@@ -232,11 +232,11 @@ export const makeDesktopBackendManager = Effect.fn("makeDesktopBackendManager")(
           .exists(config.entryPath)
           .pipe(Effect.orElseSucceed(() => false));
 
+        yield* cancelRestart;
         yield* Ref.update(state, (latest) => ({
           ...latest,
           desiredRunning: true,
           ready: false,
-          restartFiber: Option.none(),
         }));
 
         if (!entryExists) {