refactor(shared): reuse isPidAlive

src/shared/pid-alive.ts

@@ -0,0 +1,11 @@
+export function isPidAlive(pid: number): boolean {
+  if (!Number.isFinite(pid) || pid <= 0) {
+    return false;
+  }
+  try {
+    process.kill(pid, 0);
+    return true;
+  } catch {
+    return false;
+  }
+}