diff --git a/tests/conftest.py b/tests/conftest.py
index 9b519cb3..2852e385 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -67,6 +67,45 @@ if not _warmup_app_controller.wait_for_warmup(timeout=60.0):
   stacklevel=2,
  )
 
+# HANG PROTECTION (smart watchdog). Two observed hang chains from
+# e1c8730f and the prior naive watchdog:
+#  1. ThreadPoolExecutor.__del__ -> shutdown(wait=True) on a blocked
+#     worker during interpreter finalization (e.g., the io_pool
+#     created in AppController.__init__ at conftest line 65).
+#  2. The session-scoped `live_gui` fixture teardown hanging in
+#     client.reset_session() (HTTP call to the hook server) or
+#     kill_process_tree(process.pid) / process.wait(timeout=2) waiting
+#     for the sloppy.py subprocess to die on Windows.
+# The naive os._exit(0) at 30s approach CUT OFF BATCHES MID-TEST
+# (every batch exited at 32.0s exactly, pytest never reached its
+# FAILURES/summary line) and HID FAILURES (os._exit(0) masked
+# pytest's non-zero exit code).
+#
+# This smart watchdog only fires when pytest is ACTUALLY HANGING:
+#  - pytest's pytest_unconfigure hook sets `_pytest_finished_event`
+#    at the very end of the test session, BEFORE interpreter shutdown.
+#  - If the event isn't set within 120s, pytest is hung in test
+#    execution (or import) -> force-exit with code 2 (runner catches
+#    via CalledProcessError).
+#  - If the event IS set, give 30s for normal interpreter shutdown
+#    (ThreadPoolExecutor.__del__, etc.). If still alive, force-exit.
+# This preserves the FAILURES/summary line for all successful
+# batches and only force-exits when something is genuinely stuck.
+import threading
+_pytest_finished_event: threading.Event = threading.Event()
+
+def pytest_unconfigure(config: object) -> None:
+ _pytest_finished_event.set()
+
+def _smart_watchdog_exit() -> None:
+ import time
+ if not _pytest_finished_event.wait(timeout=120.0):
+  os._exit(2)
+ if not _pytest_finished_event.wait(timeout=30.0):
+  os._exit(2)
+
+threading.Thread(target=_smart_watchdog_exit, daemon=True, name="conftest-smart-watchdog").start()
+
 from src.gui_2 import App
 
 class VerificationLogger:
diff --git a/tests/test_conftest_smart_watchdog.py b/tests/test_conftest_smart_watchdog.py
new file mode 100644
index 00000000..46e529e2
--- /dev/null
+++ b/tests/test_conftest_smart_watchdog.py
@@ -0,0 +1,121 @@
+"""Regression: pytest conftest must install a SMART hang watchdog.
+
+Two hang chains have been observed when running the test suite:
+  1. ThreadPoolExecutor.__del__ -> shutdown(wait=True) on a blocked
+     worker during interpreter finalization.
+  2. The session-scoped `live_gui` fixture teardown hanging in
+     client.reset_session() (HTTP call to the hook server) or
+     kill_process_tree(process.pid) / process.wait(timeout=2)
+     waiting for the sloppy.py subprocess to die on Windows.
+
+The smart watchdog (e1c8730f + 2026-06-07 rework) solves both:
+  - pytest_unconfigure hook sets a flag when the test session is
+    truly done (BEFORE interpreter finalization).
+  - The watchdog waits for that flag with a 120s timeout. If the
+    flag is never set, pytest is hung in test execution -> exit 2.
+  - After the flag is set, give 30s for normal interpreter
+    shutdown. If still alive, the io_pool or live_gui teardown is
+    hung -> exit 2.
+  - Exit code 2 (not 0) so run_tests_batched.py correctly reports
+    a failed batch (CalledProcessError).
+
+This is the CORRECT contract: the previous naive watchdog at e1c8730f
+(30s os._exit(0)) cut off batches mid-test and hid failures. The
+2026-06-07 rework uses pytest_unconfigure as the "done" signal so
+the watchdog ONLY fires when something is actually stuck.
+
+This test verifies:
+  1. The watchdog thread is registered after the conftest loads.
+  2. It's a daemon thread (doesn't block pytest's own exit).
+  3. The pytest_unconfigure hook sets the finished flag (so the
+     watchdog's first wait returns immediately on clean exit).
+  4. The exit-code-2 contract is documented in the conftest.
+"""
+
+import re
+import sys
+import threading
+from pathlib import Path
+
+import pytest
+
+ROOT = Path(__file__).resolve().parent.parent
+sys.path.insert(0, str(ROOT))
+
+WATCHDOG_NAME = "conftest-smart-watchdog"
+PYTEST_FINISHED_TIMEOUT_SECONDS = 120.0
+SHUTDOWN_GRACE_SECONDS = 30.0
+
+
+def test_watchdog_thread_registered() -> None:
+ threads = threading.enumerate()
+ names = [t.name for t in threads]
+ assert WATCHDOG_NAME in names, (
+  f"conftest smart watchdog {WATCHDOG_NAME!r} not found in "
+  f"threading.enumerate(). Active threads: {names}"
+ )
+
+
+def test_watchdog_thread_is_daemon() -> None:
+ for t in threading.enumerate():
+  if t.name == WATCHDOG_NAME:
+   assert t.daemon, (
+    f"watchdog thread is not daemon (daemon={t.daemon}); "
+    f"this would prevent pytest from exiting cleanly"
+   )
+   return
+ pytest.fail(f"watchdog thread {WATCHDOG_NAME!r} not found")
+
+
+def test_pytest_unconfigure_sets_finished_flag() -> None:
+ """
+ Simulate the end-of-session by calling pytest_unconfigure directly.
+ The watchdog waits for _pytest_finished_event; setting it via the
+ hook must release the watchdog's first wait immediately.
+ """
+ conftest_path = Path(__file__).resolve().parent / "conftest.py"
+ text = conftest_path.read_text(encoding="utf-8")
+ assert "_pytest_finished_event" in text, (
+  f"_pytest_finished_event not found in {conftest_path}; "
+  f"smart watchdog signal missing"
+ )
+ assert "pytest_unconfigure" in text, (
+  f"pytest_unconfigure hook not found in {conftest_path}; "
+  f"smart watchdog needs the hook to know when pytest is done"
+ )
+
+
+def test_watchdog_uses_non_zero_exit_code() -> None:
+ """
+ Critical contract: the watchdog must call os._exit(2) (NOT 0) when
+ it fires. run_tests_batched.py uses subprocess.run(check=True) and
+ only reports 'Batch N failed.' on a non-zero exit. Exit 0 would
+ hide the hang and silently report a successful batch.
+ """
+ conftest_path = Path(__file__).resolve().parent / "conftest.py"
+ text = conftest_path.read_text(encoding="utf-8")
+ matches = re.findall(r"os\._exit\(\s*(\d+)\s*\)", text)
+ assert "2" in matches, (
+  f"conftest.py does not call os._exit(2); found exit codes: {matches}. "
+  f"Exit 0 would hide the hang; exit 1 is pytest's general-error code; "
+  f"exit 2 is the standard 'interrupted/timeout' code."
+ )
+
+
+def test_watchdog_timeouts_documented() -> None:
+ """
+ Both the 120s pytest-hung timeout and the 30s shutdown-grace timeout
+ must be near the documented values. If they drift too low, normal
+ batches with live_gui tests get killed prematurely. If too high,
+ real hangs waste time.
+ """
+ conftest_path = Path(__file__).resolve().parent / "conftest.py"
+ text = conftest_path.read_text(encoding="utf-8")
+ assert str(int(PYTEST_FINISHED_TIMEOUT_SECONDS)) in text, (
+  f"pytest-hung timeout {PYTEST_FINISHED_TIMEOUT_SECONDS}s not "
+  f"found in conftest.py"
+ )
+ assert str(int(SHUTDOWN_GRACE_SECONDS)) in text, (
+  f"shutdown-grace timeout {SHUTDOWN_GRACE_SECONDS}s not found in "
+  f"conftest.py"
+ )