perf(tests): bound Notes server descendant cleanup

tests/test_notes_native_cleanup.py

@@ -0,0 +1,43 @@
+"""A detached Notes descendant must not hold output open or kill a bystander."""
+import os
+import runpy
+import subprocess
+import sys
+from pathlib import Path
+
+import pytest
+from src import process_lifecycle as lifecycle
+
+ROOT = Path(__file__).resolve().parents[1]
+
+
+@pytest.mark.skipif(os.name == "nt", reason="POSIX detached-session regression; Windows uses taskkill tree")
+def test_notes_cleanup_reaps_detached_pipe_holder_and_preserves_bystander():
+    stop = runpy.run_path(str(ROOT / "scripts/verify_notes_browser_runtime.py"))["_stop_owned_server"]
+    child = "import time; time.sleep(60)"
+    program = ("import subprocess,sys,time; "
+               f"p=subprocess.Popen([sys.executable,'-c',{child!r}],start_new_session=True); "
+               "print(p.pid,flush=True); time.sleep(60)")
+    with subprocess.Popen([sys.executable, "-c", child]) as bystander:
+        server = subprocess.Popen([sys.executable, "-c", program], stdout=subprocess.PIPE,
+                                  stderr=subprocess.STDOUT, text=True, start_new_session=True)
+        root_identity = lifecycle.ProcessIdentity.capture(server.pid)
+        detached = None
+        try:
+            child_pid = int(server.stdout.readline())
+            detached = lifecycle.ProcessIdentity.capture(child_pid)
+            assert os.getpgid(child_pid) == child_pid
+            stop(server, root_identity)
+            assert server.poll() is not None
+            assert detached.exited()
+            assert bystander.poll() is None, "cleanup touched an unrelated process"
+        finally:
+            # Test-owned fallback cleanup also runs when the negative control
+            # intentionally substitutes the old parent-only teardown.
+            targets = [identity for identity in (detached, root_identity) if identity]
+            lifecycle.terminate_identities(targets, steps=lifecycle.term_kill_steps(1))
+            server.wait(timeout=3)
+            if server.stdout:
+                server.stdout.close()
+            bystander.terminate()
+            bystander.wait(timeout=3)