fix: harden instance lock compatibility semantics

Co-authored-by: Haze <hazeone@users.noreply.github.com>

tests/unit/signal-quit.test.ts

@@ -0,0 +1,15 @@
+import { describe, expect, it, vi } from 'vitest';
+import { createSignalQuitHandler } from '@electron/main/signal-quit';
+
+describe('signal quit handler', () => {
+  it('logs and requests quit when signal is received', () => {
+    const logInfo = vi.fn();
+    const requestQuit = vi.fn();
+    const handler = createSignalQuitHandler({ logInfo, requestQuit });
+
+    handler('SIGTERM');
+
+    expect(logInfo).toHaveBeenCalledWith('Received SIGTERM; requesting app quit');
+    expect(requestQuit).toHaveBeenCalledTimes(1);
+  });
+});