test(runtime): add focused supervisor runtime coverage

- Split auth, status cache, terminal env, and prompt write tests
- Isolate start/close manager tests with temp dirs and disposal
- Update app pending launch expectation to launching status

Author: SDSLeon

src/renderer/app.test.tsx

@@ -627,7 +627,10 @@ describe("App", () => {
     fireEvent.click(await screen.findByText("open-thread-1"));
 
     await waitFor(() => {
-      expect(screen.getByTestId("thread-view-thread-1")).toHaveAttribute("data-status", "inactive");
+      expect(screen.getByTestId("thread-view-thread-1")).toHaveAttribute(
+        "data-status",
+        "launching",
+      );
       expect(screen.getByTestId("thread-view-thread-1")).toHaveAttribute("data-pending-launch", "");
     });
     expect(bridge.startThread).not.toHaveBeenCalled();