diff --git a/tests/background_stops.py b/tests/background_stops.py
new file mode 100644
index 0000000..9aeb07a
--- /dev/null
+++ b/tests/background_stops.py
@@ -0,0 +1,27 @@
+"""Final stops for the background threads a test starts (#301, #302).
+
+Every real ``ImageGenerationHandler``, ``ImageMonitor`` or ``PromptTracker``
+a test constructs ends with its final stop and an assertion, before the
+test's folder and databases go: ``close()`` for a handler,
+``stop_monitoring()`` for a monitor, ``shutdown()`` for a tracker.
+"""
+
+from utils.prompt_tracker import PromptTracker
+
+
+def stop_tracker(testcase, tracker):
+    """Shut a real tracker's cleanup thread down; mocks are left alone."""
+    if isinstance(tracker, PromptTracker):
+        testcase.assertTrue(tracker.shutdown(), "prompt cleanup thread still running")
+
+
+def close_handler(testcase, handler):
+    """Close ``handler`` for good, then stop the tracker it was built with."""
+    testcase.assertTrue(handler.close(), "image worker still running")
+    stop_tracker(testcase, getattr(handler, "prompt_tracker", None))
+
+
+def stop_monitor(testcase, monitor):
+    """Stop ``monitor`` (its observer and worker), then its tracker."""
+    testcase.assertTrue(monitor.stop_monitoring(), "image monitor still running")
+    stop_tracker(testcase, getattr(monitor, "prompt_tracker", None))
diff --git a/tests/browser/workspace_system_fixture.py b/tests/browser/workspace_system_fixture.py
index 0fc36d9..9900abc 100644
--- a/tests/browser/workspace_system_fixture.py
+++ b/tests/browser/workspace_system_fixture.py
@@ -97,15 +97,25 @@ def register_system_commands(app, routes, api, root: Path):
     real_move = library_move.move_library
     keep = PromptManagerConfig.KEEP_LIBRARY_IN_NODE_FOLDER
     config_bytes = config_path.read_bytes() if config_path.exists() else None
-    host_values = (
-        PromptManagerConfig.RESULT_TIMEOUT,
-        PromptManagerConfig.WEBUI_DISPLAY_MODE,
-        PromptManagerConfig.WORKER_THREADS,
-        GalleryConfig.MONITORING_ENABLED,
-        PromptManagerConfig.THUMBNAIL_FORMAT,
-        PromptManagerConfig.THUMBNAIL_QUALITY,
-        PromptManagerConfig.THUMBNAIL_EDGE,
+    from py.api.settings_routes import (
+        _AUTOTAG_SETTINGS,
+        _GALLERY_SETTINGS,
+        _SETTINGS_FILE_KEYS,
     )
+
+    # Every value POST /settings can change, so a reset restores each one
+    # (a saved safety_backup=false once leaked into a later spec's review).
+    # The tagging settings are the tagging fixture's to reset.
+    host_values = {
+        (GalleryConfig if name in _GALLERY_SETTINGS else PromptManagerConfig, name): (
+            getattr(
+                GalleryConfig if name in _GALLERY_SETTINGS else PromptManagerConfig,
+                name,
+            )
+        )
+        for name in _SETTINGS_FILE_KEYS
+        if name not in _AUTOTAG_SETTINGS
+    }
     from py.api import thumbnail_encode
 
     monitor = getattr(image_monitor, "_monitor_instance", None)
@@ -135,15 +145,8 @@ def register_system_commands(app, routes, api, root: Path):
             unplugged.rmdir()
         GalleryConfig.MONITORING_DIRECTORIES = list(configured)
         api._health_report = None
-        (
-            PromptManagerConfig.RESULT_TIMEOUT,
-            PromptManagerConfig.WEBUI_DISPLAY_MODE,
-            PromptManagerConfig.WORKER_THREADS,
-            GalleryConfig.MONITORING_ENABLED,
-            PromptManagerConfig.THUMBNAIL_FORMAT,
-            PromptManagerConfig.THUMBNAIL_QUALITY,
-            PromptManagerConfig.THUMBNAIL_EDGE,
-        ) = host_values
+        for (owner, name), value in host_values.items():
+            setattr(owner, name, value)
         thumbnail_encode.reset_encoders()
         image_monitor._monitor_instance = monitor
         api.__dict__.pop("_library_resolver", None)
diff --git a/tests/comfyui/fixtures/ledger_nodes.py b/tests/comfyui/fixtures/ledger_nodes.py
index c65199c..80914ff 100644
--- a/tests/comfyui/fixtures/ledger_nodes.py
+++ b/tests/comfyui/fixtures/ledger_nodes.py
@@ -1,5 +1,6 @@
 """Deterministic nodes and queue controls installed only in an owned test host."""
 
+import asyncio
 import os
 import threading
 import time
@@ -291,7 +292,8 @@ async def image_monitor(request: web.Request) -> web.Response:
         config.MONITORING_ENABLED = True
         monitor.start_monitoring([folder_paths.get_output_directory()])
     else:
-        monitor.stop_monitoring()
+        # Joins the image worker and the observer (up to 5 s each): off the loop.
+        await asyncio.to_thread(monitor.stop_monitoring)
         config.MONITORING_ENABLED = False
     return web.json_response({"monitoring": monitor.is_monitoring})
 
diff --git a/tests/test_execution_history_hooks.py b/tests/test_execution_history_hooks.py
index ae790d2..b0f5454 100644
--- a/tests/test_execution_history_hooks.py
+++ b/tests/test_execution_history_hooks.py
@@ -28,6 +28,8 @@ except ImportError:
 
 Status = namedtuple("ExecutionStatus", "status_str completed messages")
 JOB = "a0c26da3-eb26-405c-b143-c662a84c3112"
+# A cross-thread wait or a duration check fails only past this (#370).
+CEILING_SECONDS = 30.0
 
 
 class HostQueue:
@@ -209,6 +211,9 @@ class HistoryHooksTests(unittest.TestCase):
         self.queue.get = unrelated_after
         self.dequeue(0)
         self.queue.task_done(0, {}, status())
+        # The writer drains first: this test checks wrappers and the session,
+        # not the 2 s bound, which a slow runner can spend on the write (#370).
+        self.drain(first)
         self.assertTrue(first.dispose())
         self.assertTrue(first.dispose())
         self.assertIs(self.queue.get, unrelated_after)
@@ -339,15 +344,17 @@ class HistoryHooksTests(unittest.TestCase):
         with patch.object(self.db, "write_execution_start", blocked):
             registration = self.register()
             self.dequeue(0)
-            self.assertTrue(entered.wait(1))
+            # Ceilings, not tight wall clocks (#370): the return values show
+            # the bound; a ceiling still fails a call that waits unbounded.
+            self.assertTrue(entered.wait(CEILING_SECONDS))
             began = time.monotonic()
             self.queue.task_done(0, {}, status())
             self.dequeue(1)
-            self.assertLess(time.monotonic() - began, 0.2)
+            self.assertLess(time.monotonic() - began, CEILING_SECONDS)
             began = time.monotonic()
             self.assertFalse(registration.dispose())
             self.assertGreaterEqual(time.monotonic() - began, 1.8)
-            self.assertLess(time.monotonic() - began, 2.3)
+            self.assertLess(time.monotonic() - began, CEILING_SECONDS)
             release.set()
             self.assertTrue(registration.dispose(2))
 
diff --git a/tests/test_execution_history_writer.py b/tests/test_execution_history_writer.py
index ec6327d..1d93dcb 100644
--- a/tests/test_execution_history_writer.py
+++ b/tests/test_execution_history_writer.py
@@ -642,6 +642,8 @@ class HistoryWriterTests(unittest.TestCase):
                 == "succeeded"
             )
             self.assertTrue(writer.submit(self.start_command(2)))
+            # Drain first: the 2 s bound is not under test here (#370).
+            drain_writer(writer)
             self.assertTrue(writer.close(2))
         self.assertEqual(len(set(threads)), 1)
         self.assertNotEqual(threads[0], threading.get_ident())
diff --git a/tests/test_execution_output_hooks.py b/tests/test_execution_output_hooks.py
index cf27a8c..567a596 100644
--- a/tests/test_execution_output_hooks.py
+++ b/tests/test_execution_output_hooks.py
@@ -245,6 +245,8 @@ class OutputHooksTests(fixtures.unittest.TestCase):
         registration = self.register()
         self.dequeue(0)
         late = registration._task_done
+        # Drain first: the 2 s bound is not under test here (#370).
+        self.drain(registration)
         self.assertTrue(registration.dispose())
         thread = threading.Thread(
             target=lambda: late((0, history(), fixtures.status()), {})
diff --git a/tests/test_execution_output_writer.py b/tests/test_execution_output_writer.py
index c91a49e..c9f89d4 100644
--- a/tests/test_execution_output_writer.py
+++ b/tests/test_execution_output_writer.py
@@ -17,6 +17,7 @@ from utils.execution_contexts import MAX_ATTEMPT_BYTES
 from utils.execution_output_capture import seal_outputs
 from utils.execution_outputs import snapshot_output_roots
 from utils.execution_history_writer import HistoryWriter
+from tests.history_waits import drain_writer
 
 try:
     from tests import test_execution_history_writer as fixtures
@@ -161,6 +162,8 @@ class OutputWriterTests(fixtures.unittest.TestCase):
         start = replace(self.start_command(), run_id=str(fixtures.uuid4()))
         self.assertTrue(writer.submit(start))
         self.finalization(writer, start)
+        # Drain first: the 2 s bound is not under test here (#370).
+        drain_writer(writer)
         self.assertTrue(writer.close(2))
         self.assertEqual(
             self.db.get_execution_run(start.run_id)["outcome"], "succeeded"
diff --git a/tests/test_hashing.py b/tests/test_hashing.py
index 9a262be..ad02cdf 100644
--- a/tests/test_hashing.py
+++ b/tests/test_hashing.py
@@ -12,6 +12,7 @@ import unittest
 
 sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
 
+from tests.background_stops import stop_tracker  # noqa: E402
 from utils.hashing import (
     generate_prompt_hash,
     is_duplicate_prompt,
@@ -49,6 +50,7 @@ class TestSingleHashImplementation(unittest.TestCase):
         db = mock.Mock()
         db.get_prompt_by_hash.return_value = {"id": 42}
         tracker = PromptTracker(db)
+        self.addCleanup(stop_tracker, self, tracker)
         tracker.set_current_prompt("  Hello World  ")
         db.get_prompt_by_hash.assert_called_once_with(
             generate_prompt_hash("  Hello World  ")
diff --git a/tests/test_image_linking.py b/tests/test_image_linking.py
index 65cc015..3cc8586 100644
--- a/tests/test_image_linking.py
+++ b/tests/test_image_linking.py
@@ -8,6 +8,7 @@ import unittest.mock as mock
 
 sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
 
+from tests.background_stops import close_handler  # noqa: E402
 from database.operations import PromptDatabase
 from utils.hashing import generate_prompt_hash
 from utils.image_monitor import ImageGenerationHandler
@@ -52,6 +53,7 @@ class LinkingTestCase(unittest.TestCase):
         )
 
     def tearDown(self):
+        close_handler(self, self.handler)  # and the tracker's cleanup thread
         self.db.close_all()  # Windows cannot unlink an open database file
         for path in (
             self.image,
diff --git a/tests/test_image_monitor_singleton.py b/tests/test_image_monitor_singleton.py
index c77811c..0b90716 100644
--- a/tests/test_image_monitor_singleton.py
+++ b/tests/test_image_monitor_singleton.py
@@ -136,13 +136,21 @@ class TestMonitorSingletonLifecycle(unittest.TestCase):
 
 
 class FakeObserver:
-    """Records what the monitor does with the watchdog observer."""
+    """Records what the monitor does with the watchdog observer.
 
-    def __init__(self):
+    ``calls`` lists ``stop`` and ``join`` in order (shared with a test's own
+    recorders when given); ``stay_alive`` keeps it alive after ``join``;
+    ``stop_error`` makes ``stop`` raise.
+    """
+
+    def __init__(self, calls=None, stay_alive=False, stop_error=None):
         self.scheduled = []
         self.started = False
         self.stopped = False
         self.joined = False
+        self.calls = calls if calls is not None else []
+        self.stay_alive = stay_alive
+        self.stop_error = stop_error
 
     def schedule(self, handler, path, recursive=False):
         self.scheduled.append((handler, path, recursive))
@@ -151,12 +159,18 @@ class FakeObserver:
         self.started = True
 
     def stop(self):
+        self.calls.append(("stop",))
+        if self.stop_error is not None:
+            raise self.stop_error
         self.stopped = True
 
     def join(self, timeout=None):
+        self.calls.append(("join", timeout))
         self.joined = True
 
     def is_alive(self):
+        if self.stay_alive:
+            return self.started
         return self.started and not self.stopped
 
 
@@ -171,6 +185,8 @@ class TestStartStop(unittest.TestCase):
         self.missing = os.path.join(self.tmp.name, "does-not-exist")
 
     def tearDown(self):
+        # Before the folder is removed (addCleanup runs after tearDown).
+        self.assertTrue(self.monitor.stop_monitoring())
         im_mod._monitor_instance = None
 
     def test_only_nonexistent_directories_leaves_monitoring_off(self):
@@ -225,9 +241,8 @@ class TestStartStop(unittest.TestCase):
         worker = handler._worker
         self.assertTrue(worker.is_alive())
 
-        self.monitor.stop_monitoring()
+        self.assertTrue(self.monitor.stop_monitoring())
 
-        worker.join(timeout=2)
         self.assertFalse(worker.is_alive())
         self.assertEqual(handler.pending_count(), 0)
         # A restart gets a fresh handler and observer
@@ -303,6 +318,61 @@ class TestStartStop(unittest.TestCase):
         self.assertEqual(self.monitor.monitored_directories, [self.tmp.name])
         self.monitor.stop_monitoring()
 
+    def _start_with(self, fake):
+        with patch.object(im_mod, "Observer", return_value=fake):
+            self.monitor.start_monitoring([self.tmp.name])
+        handler = self.monitor.handler
+        real_close = handler.close
+
+        def close(timeout=im_mod.WORKER_JOIN_SECONDS):
+            fake.calls.append(("close",))
+            return real_close(timeout)
+
+        handler.close = close
+        return handler
+
+    def test_stop_monitoring_joins_observer_and_worker(self):
+        fake = FakeObserver()
+        handler = self._start_with(fake)
+
+        self.assertTrue(self.monitor.stop_monitoring(timeout=3.0))
+
+        self.assertEqual([c[0] for c in fake.calls], ["close", "stop", "join"])
+        join_timeout = fake.calls[2][1]
+        self.assertIsNotNone(join_timeout)
+        self.assertLessEqual(join_timeout, 3.0)
+        self.assertTrue(handler._closed)
+
+    def test_stop_monitoring_reports_an_observer_still_running(self):
+        fake = FakeObserver(stay_alive=True)
+        self._start_with(fake)
+        with self.assertLogs("prompt_manager.image_monitor", "WARNING") as logs:
+            self.assertFalse(self.monitor.stop_monitoring(timeout=0.05))
+        self.assertIn("watchdog observer still running", "\n".join(logs.output))
+        self.assertFalse(self.monitor.is_monitoring)
+        fake.stay_alive = False  # it ends; tearDown's stop waits for it
+
+    def test_a_second_stop_monitoring_waits_for_the_observer(self):
+        fake = FakeObserver(stay_alive=True)
+        self._start_with(fake)
+        with self.assertLogs("prompt_manager.image_monitor", "WARNING"):
+            self.assertFalse(self.monitor.stop_monitoring(timeout=0.05))
+            self.assertFalse(self.monitor.stop_monitoring(timeout=0.05))
+        fake.stay_alive = False
+        self.assertTrue(self.monitor.stop_monitoring())
+        self.assertFalse(self.monitor._unfinished)
+
+    def test_stop_monitoring_reports_an_observer_stop_that_raised(self):
+        fake = FakeObserver(stop_error=OSError("descriptor gone"))
+        self._start_with(fake)
+        with self.assertLogs("prompt_manager.image_monitor", "WARNING") as logs:
+            self.assertFalse(self.monitor.stop_monitoring())
+        self.assertIn("Error while stopping image monitoring", "\n".join(logs.output))
+        fake.stop_error = None  # tearDown's stop calls stop() again
+
+    def test_stop_monitoring_without_an_observer_returns_true(self):
+        self.assertTrue(self.monitor.stop_monitoring())
+
 
 class FakeEvent:
     def __init__(self, path, is_directory=False):
@@ -335,6 +405,10 @@ class TestHandlerScheduling(unittest.TestCase):
             self.processed.append((path, prompt_snapshot))
         )
 
+    def tearDown(self):
+        # Before the folder is removed (addCleanup runs after tearDown).
+        self.assertTrue(self.handler.close())
+
     def _image(self, name, content=b"x" * 16):
         path = os.path.join(self.tmp.name, name)
         with open(path, "wb") as f:
@@ -399,23 +473,127 @@ class TestHandlerScheduling(unittest.TestCase):
         empty = self._image("empty.png", content=b"")
         self.assertFalse(self.handler.wait_until_settled(empty))
 
-    def test_shutdown_stops_the_worker_and_clears_pending(self):
+    def test_shutdown_joins_the_worker_within_the_bound(self):
         self.handler.processing_delay = 10  # keep the first image waiting
         self.handler.schedule(self._image("s1.png"))
         self.handler.schedule(self._image("s2.png"))
         worker = self.handler._worker
         self.assertTrue(worker.is_alive())
 
-        self.handler.shutdown()
+        self.assertTrue(self.handler.shutdown())
 
-        worker.join(timeout=2)
         self.assertFalse(worker.is_alive())
         self.assertEqual(self.handler.pending_count(), 0)
 
+    def test_shutdown_reports_a_worker_still_busy(self):
+        entered, release = threading.Event(), threading.Event()
+
+        def busy(path, prompt_snapshot=None):
+            entered.set()
+            release.wait(30)
+
+        self.handler.process_new_image = busy
+        self.handler.schedule(self._image("busy.png"))
+        worker = self.handler._worker
+        self.addCleanup(worker.join, 30)
+        self.addCleanup(release.set)
+        self.assertTrue(entered.wait(30), "the worker never took the image")
+
+        with self.assertLogs("prompt_manager.image_monitor", "WARNING") as logs:
+            self.assertFalse(self.handler.shutdown(timeout=0.05))
+        self.assertIn("image worker still running", "\n".join(logs.output))
+
+        release.set()
+        worker.join(30)
+        self.assertFalse(worker.is_alive())
+
+    def test_a_second_stop_waits_for_a_worker_still_finishing(self):
+        entered, release = threading.Event(), threading.Event()
+
+        def busy(path, prompt_snapshot=None):
+            entered.set()
+            release.wait(30)
+
+        self.handler.process_new_image = busy
+        self.handler.schedule(self._image("twice.png"))
+        worker = self.handler._worker
+        self.addCleanup(worker.join, 30)
+        self.addCleanup(release.set)
+        self.assertTrue(entered.wait(30), "the worker never took the image")
+
+        with self.assertLogs("prompt_manager.image_monitor", "WARNING"):
+            self.assertFalse(self.handler.close(timeout=0.05))
+            self.assertFalse(self.handler.close(timeout=0.05))
+        release.set()
+        self.assertTrue(self.handler.close(timeout=30))
+        self.assertFalse(worker.is_alive())
+
+    def test_shutdown_on_the_worker_itself_only_signals(self):
+        entered, result = threading.Event(), {}
+
+        def stop_from_inside(path, prompt_snapshot=None):
+            result["value"] = self.handler.shutdown()
+            entered.set()
+
+        self.handler.process_new_image = stop_from_inside
+        self.handler.schedule(self._image("self.png"))
+        worker = self.handler._worker
+        self.assertTrue(entered.wait(30), "the worker never took the image")
+        worker.join(30)
+        self.assertFalse(result["value"])
+        self.assertFalse(worker.is_alive())
+
+    def _live_workers(self):
+        return {
+            t for t in threading.enumerate() if t.name == "PromptManagerImageWorker"
+        }
+
+    def _seal(self, handler, name):
+        handler._await_history(os.path.join(self.tmp.name, name))
+        handler._on_outputs_sealed(
+            "run-1",
+            [{"folder_type": "output", "subfolder": "", "filename": name}],
+        )
+
+    def test_close_refuses_new_work(self):
+        path = self._image("late.png")
+        with patch.object(im_mod, "host_output_directory", return_value=self.tmp.name):
+            self.assertTrue(self.handler.close())
+            before = self._live_workers()
+            self.assertFalse(self.handler.schedule(path))
+            # The image in hand can still ask for a history re-check and its
+            # run can be sealed afterwards, on the history writer's thread.
+            self.handler._await_history(path)
+            self.assertEqual(self.handler.awaiting_history(), [])
+            self._seal(self.handler, "late.png")
+            self.handler._schedule_recheck(path)
+        self.assertIsNone(self.handler._worker)
+        self.assertEqual(list(self.handler._history_due), [])
+        self.assertEqual(self._live_workers() - before, set())
+
+    def test_a_sealed_run_starts_a_worker_on_an_open_handler(self):
+        self._image("open.png")
+        with patch.object(im_mod, "host_output_directory", return_value=self.tmp.name):
+            self._seal(self.handler, "open.png")
+        self.assertIsNotNone(self.handler._worker)
+        self.assertTrue(self.handler.close())
+
+    def test_close_is_idempotent(self):
+        self.handler.schedule(self._image("c1.png"))
+        self.assertTrue(self.handler.close())
+        self.assertTrue(self.handler.close())
+
+    def test_on_created_after_close_takes_no_lock(self):
+        self.assertTrue(self.handler.close())
+        self.handler.on_created(FakeEvent(self._image("after.png")))
+        self.tracker.keyed_snapshot.assert_not_called()
+        self.assertEqual(self.handler.pending_count(), 0)
+
     def test_shutdown_is_idempotent_and_safe_before_start(self):
         fresh = im_mod.ImageGenerationHandler(MagicMock(), self.tracker)
-        fresh.shutdown()
-        fresh.shutdown()
+        self.assertTrue(fresh.shutdown())
+        self.assertTrue(fresh.shutdown())
+        self.assertTrue(fresh.close())
         self.handler.schedule(self._image("s3.png"))
         self.assertTrue(wait_for(lambda: self.handler.pending_count() == 0))
         self.handler.shutdown()
@@ -434,7 +612,7 @@ class TestHandlerScheduling(unittest.TestCase):
         self.assertTrue(wait_for(lambda: self.handler.pending_count() == 0))
         self.assertIn(path, [p for p, _ in self.processed])
         self.assertIsNot(self.handler._worker, old_worker)
-        self.handler.shutdown()
+        self.assertTrue(self.handler.close())
 
     def test_processing_errors_do_not_kill_the_worker(self):
         def explode(path, prompt_snapshot=None):
@@ -449,6 +627,47 @@ class TestHandlerScheduling(unittest.TestCase):
         self.assertEqual(self.processed, [first, second])
 
 
+class TestCloseReleasesHandles(unittest.TestCase):
+    """``close`` joins the worker, so the test folder can be removed (#302)."""
+
+    def test_close_releases_handles(self):
+        from PIL import Image
+
+        from database.operations import PromptDatabase
+        from tests.open_handles import assert_closed
+        from utils.prompt_tracker import PromptTracker
+
+        with tempfile.TemporaryDirectory() as folder:
+            db = PromptDatabase(os.path.join(folder, "prompts.db"))
+            tracker = PromptTracker(db)
+            handler = im_mod.ImageGenerationHandler(db, tracker)
+            handler.processing_delay = 0
+            handler.settle_interval = 0.01
+            done = threading.Event()
+            real_process = handler.process_new_image
+
+            def process(path, prompt_snapshot=None):
+                try:
+                    real_process(path, prompt_snapshot=prompt_snapshot)
+                finally:
+                    done.set()
+
+            handler.process_new_image = process
+            path = os.path.join(folder, "real.png")
+            Image.new("RGB", (8, 8), "red").save(path)
+            try:
+                self.assertTrue(handler.schedule(path))
+                worker = handler._worker
+                self.assertTrue(done.wait(30), "the worker never processed the image")
+            finally:
+                closed, shut = handler.close(), tracker.shutdown()
+                db.model.close_all()
+            self.assertTrue(closed)
+            self.assertTrue(shut)
+            self.assertFalse(worker.is_alive())
+            assert_closed(self, folder)
+
+
 class TestOutputListener(unittest.TestCase):
     """Every settled output is reported to the Images listing (#348, PR 2)."""
 
@@ -456,7 +675,7 @@ class TestOutputListener(unittest.TestCase):
         self.tmp = tempfile.TemporaryDirectory()
         self.addCleanup(self.tmp.cleanup)
         self.handler = im_mod.ImageGenerationHandler(MagicMock(), MagicMock())
-        self.addCleanup(self.handler.shutdown)
+        self.addCleanup(lambda: self.assertTrue(self.handler.close()))
         self.handler.processing_delay = 0
         self.handler.settle_interval = 0.01
         self.handler.process_new_image = lambda path, prompt_snapshot=None: None
@@ -549,7 +768,7 @@ class TestOutputListener(unittest.TestCase):
             self.assertIsNone(monitor.output_listener)
             self.assertIsNone(monitor.handler.output_listener)
         finally:
-            monitor.stop_monitoring()
+            self.assertTrue(monitor.stop_monitoring())
 
 
 class TestModuleIsolation(unittest.TestCase):
diff --git a/tests/test_library_move_review.py b/tests/test_library_move_review.py
index 14e5d52..57f61c3 100644
--- a/tests/test_library_move_review.py
+++ b/tests/test_library_move_review.py
@@ -29,6 +29,7 @@ sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
 from database import library_move as lm  # noqa: E402
 from database import models  # noqa: E402
 from database.operations import PromptDatabase  # noqa: E402
+from tests.background_stops import close_handler  # noqa: E402
 from tests.open_handles import assert_closed  # noqa: E402
 from utils import library_location as ll  # noqa: E402
 from utils import usage_tracking  # noqa: E402
@@ -204,6 +205,7 @@ class TestBackgroundWritesSurviveTheSwitch(_MoveCase):
         image = os.path.join(self.comfy, "output", "late.png")
         writer_db = PromptDatabase(self.old_db)
         handler = ImageGenerationHandler(writer_db, mock.MagicMock())
+        self.addCleanup(close_handler, self, handler)
         started = threading.Event()
         probe = _CrossThreadCloseProbe()
         outcome = {}
@@ -256,6 +258,7 @@ class TestBackgroundWritesSurviveTheSwitch(_MoveCase):
 
         db = PromptDatabase(self.old_db)
         handler = ImageGenerationHandler(db, mock.MagicMock())
+        self.addCleanup(close_handler, self, handler)
         image = os.path.join(self.comfy, "output", "orphan.png")
         with mock.patch.object(handler, "logger") as log:
             handler.link_image_to_prompt(image, {"id": 99999}, {})
diff --git a/tests/test_nonfinite_metadata.py b/tests/test_nonfinite_metadata.py
index 60f536d..b49729d 100644
--- a/tests/test_nonfinite_metadata.py
+++ b/tests/test_nonfinite_metadata.py
@@ -24,6 +24,7 @@ from unittest.mock import patch
 from PIL import Image, PngImagePlugin
 
 from database.operations import PromptDatabase
+from tests.background_stops import close_handler
 from tests.history_waits import drain_writer
 from tests.test_api_admin import AdminAPITestCase
 from tests.test_api_images import ImageAPITestCase
@@ -224,6 +225,7 @@ class TestMonitorIngestsNonFiniteMetadata(StrictRows, unittest.TestCase):
         self.handler.logger.disabled = True
 
     def tearDown(self):
+        close_handler(self, self.handler)
         self.db.close_all()
         assert_closed(self, self.temp.name)
         self.temp.cleanup()
diff --git a/tests/test_prompt_attribution.py b/tests/test_prompt_attribution.py
index 6171771..7cf3d10 100644
--- a/tests/test_prompt_attribution.py
+++ b/tests/test_prompt_attribution.py
@@ -23,6 +23,7 @@ try:
 except ImportError:  # discovered with tests/ as the top-level directory
     from open_handles import assert_closed
 
+from tests.background_stops import close_handler  # noqa: E402
 from database.operations import PromptDatabase
 from prompt_manager import PromptManager
 from prompt_manager_pair import PromptManagerPair
@@ -278,6 +279,7 @@ class MonitorCase(DatabaseCase):
         fd, self.image = tempfile.mkstemp(suffix=".png", dir=self.tmp.name)
         os.close(fd)
         self.handler = ImageGenerationHandler(self.db, self.tracker)
+        self.addCleanup(close_handler, self, self.handler)
         self.linked = []
         self.handler.link_image_to_prompt = lambda path, prompt, meta: (
             self.linked.append(prompt["id"])
diff --git a/tests/test_prompt_tracker.py b/tests/test_prompt_tracker.py
index a9bfdc8..35a5c9c 100644
--- a/tests/test_prompt_tracker.py
+++ b/tests/test_prompt_tracker.py
@@ -5,10 +5,12 @@ Tests PromptTracker, PromptExecutionContext, and the singleton
 get_prompt_tracker. Uses a mock db_manager to avoid database deps.
 """
 
+import logging
 import os
 import sys
 import time
 import threading
+import types
 import unittest
 from unittest.mock import MagicMock, patch
 
@@ -312,5 +314,93 @@ class TestPromptQueue(unittest.TestCase):
         self.assertEqual(popped_ids, ids)
 
 
+def _real_tracker():
+    """A PromptTracker built by its own ``__init__``, so its cleanup thread runs."""
+    mock_db = MagicMock()
+    mock_db.get_prompt_by_hash.return_value = None
+    return PromptTracker(mock_db)
+
+
+class TestTrackerShutdown(unittest.TestCase):
+    """The cleanup thread stops on a signal and is joined within a bound (#301)."""
+
+    def test_shutdown_stops_the_cleanup_thread_within_the_bound(self):
+        tracker = _real_tracker()
+        thread = tracker.cleanup_thread
+        self.assertTrue(thread.is_alive())
+        self.assertEqual(thread.name, "PromptManagerPromptCleanup")
+
+        self.assertTrue(tracker.shutdown())
+        self.assertFalse(thread.is_alive())
+
+    def test_shutdown_is_idempotent(self):
+        tracker = _real_tracker()
+        self.assertTrue(tracker.shutdown())
+        self.assertTrue(tracker.shutdown())
+
+    def test_cleanup_error_wait_is_interruptible(self):
+        import utils.prompt_tracker as tracker_mod
+
+        real_time = time.time
+        calls = {"n": 0}
+
+        def failing_once():
+            calls["n"] += 1
+            if calls["n"] == 1:
+                raise RuntimeError("clock unavailable")
+            return real_time()
+
+        stub = types.SimpleNamespace(
+            time=failing_once, sleep=time.sleep, monotonic=time.monotonic
+        )
+        logged = threading.Event()
+        logger = logging.getLogger("prompt_manager.prompt_tracker")
+        real_error = logger.error
+
+        def error(*args, **kwargs):
+            real_error(*args, **kwargs)
+            logged.set()
+
+        with (
+            patch.object(tracker_mod, "time", stub),
+            patch.object(logger, "error", side_effect=error),
+        ):
+            tracker = _real_tracker()
+            self.addCleanup(tracker.shutdown)
+            self.assertTrue(logged.wait(30), "the cleanup error was never logged")
+            # The thread is now in its 60 s error wait.
+            self.assertTrue(tracker.shutdown())
+        self.assertFalse(tracker.cleanup_thread.is_alive())
+
+    def test_tracker_works_after_shutdown(self):
+        tracker = _real_tracker()
+        self.assertTrue(tracker.shutdown())
+        tracker.set_current_prompt("still tracked", {"prompt_id": 9})
+        self.assertEqual(tracker.pop_next_prompt()["id"], 9)
+
+    def test_shutdown_of_a_tracker_built_without_init(self):
+        self.assertTrue(_make_tracker().shutdown())
+
+    def test_shutdown_on_the_cleanup_thread_only_signals(self):
+        tracker = _real_tracker()
+        self.addCleanup(lambda: self.assertTrue(tracker.shutdown()))
+        result = {}
+        with patch.object(tracker, "cleanup_thread", threading.current_thread()):
+            result["value"] = tracker.shutdown()
+        self.assertFalse(result["value"])
+        self.assertTrue(tracker._stop.is_set())
+
+    def test_shutdown_reports_a_thread_still_running(self):
+        tracker = _real_tracker()
+        self.assertTrue(tracker.shutdown())
+        busy = MagicMock()
+        busy.is_alive.return_value = True
+        tracker.cleanup_thread = busy
+        with self.assertLogs("prompt_manager.prompt_tracker", "WARNING") as logs:
+            self.assertFalse(tracker.shutdown(timeout=0.05))
+        busy.join.assert_called_once_with(0.05)
+        self.assertIn("prompt cleanup thread still running", "\n".join(logs.output))
+
+
 if __name__ == "__main__":
     unittest.main()
diff --git a/tests/test_review.py b/tests/test_review.py
index a313e31..ce79a32 100644
--- a/tests/test_review.py
+++ b/tests/test_review.py
@@ -27,6 +27,7 @@ except ImportError:  # discovered with tests/ as the top-level directory
 
 from PIL import Image, PngImagePlugin
 
+from tests.background_stops import close_handler, stop_monitor
 from database.operations import PromptDatabase
 from database.review_schema import canonical_evidence, evidence_digest
 from py.api import PromptManagerAPI
@@ -790,6 +791,7 @@ class TestReviewEdges(ReviewTestCase):
 class TestMonitorRecording(ReviewTestCase):
     def _handler(self):
         handler = ImageGenerationHandler(self.api.db, PromptTracker(self.api.db))
+        self.addCleanup(close_handler, self, handler)
         return handler
 
     def _linked_prompt(self, path):
@@ -953,7 +955,7 @@ class TestMonitorRecording(ReviewTestCase):
             monitor.set_review_recorder(None)
             self.assertIsNone(monitor.handler.review_recorder)
         finally:
-            monitor.stop_monitoring()
+            stop_monitor(self, monitor)
 
 
 if __name__ == "__main__":
@@ -1092,6 +1094,7 @@ class TestCaptureStoreShutdown(ReviewTestCase):
                 self._scan_record(path)
             # The monitor's pass records nothing, so it needs no store.
             handler = ImageGenerationHandler(self.api.db, PromptTracker(self.api.db))
+            self.addCleanup(close_handler, self, handler)
             handler.review_recorder = self.api.record_review_file
             handler._record_review(str(path))
             self.assertEqual(self.api.record_review_file(str(path)), "skipped")
diff --git a/tests/test_review_image_links_tool.py b/tests/test_review_image_links_tool.py
index a88fb10..7941e53 100644
--- a/tests/test_review_image_links_tool.py
+++ b/tests/test_review_image_links_tool.py
@@ -17,6 +17,7 @@ except ImportError:  # discovered with tests/ as the top-level directory
     from open_handles import assert_closed
 
 from database.operations import PromptDatabase
+from tests.background_stops import close_handler
 from tests.test_api_images import ImageAPITestCase
 from tests.test_prompt_attribution import issue_graph, pair_evidence
 from tools import review_image_links as tool
@@ -158,8 +159,8 @@ class ReviewToolTests(ToolFixture):
 
     def test_conflicting_sources_are_left_to_the_maintainer(self):
         db = PromptDatabase(self.db_path)
+        handler = tool.ImageGenerationHandler(db, None)
         try:
-            handler = tool.ImageGenerationHandler(db, None)
             row = {
                 "id": 1,
                 "prompt_id": self.coffee,
@@ -170,6 +171,7 @@ class ReviewToolTests(ToolFixture):
             ):
                 verdict = tool.judge(db, handler, row, self.output)
         finally:
+            close_handler(self, handler)
             db.close_all()
         self.assertEqual(verdict["verdict"], "conflict")
 
diff --git a/tests/test_review_inspection.py b/tests/test_review_inspection.py
index 36cba58..33e4f3b 100644
--- a/tests/test_review_inspection.py
+++ b/tests/test_review_inspection.py
@@ -28,6 +28,7 @@ except ImportError:  # discovered with tests/ as the top-level directory
     from test_api_review import ReviewRoutesTestCase
     from test_review import unlinkable_graph, write_png
 
+from tests.background_stops import close_handler
 from utils import inspection_semantics, review_capture
 from utils.hashing import generate_prompt_hash
 from utils.image_monitor import ImageGenerationHandler
@@ -437,6 +438,7 @@ class TestApplyInspectionCandidate(InspectionTestCase):
 class TestMonitorNeverQueues(InspectionTestCase):
     def _handler(self):
         handler = ImageGenerationHandler(self.api.db, PromptTracker(self.api.db))
+        self.addCleanup(close_handler, self, handler)
         handler.review_recorder = self.api.record_review_file
         return handler
 
@@ -760,6 +762,7 @@ class TestRecordingEdges(InspectionTestCase):
             text="latest", prompt_hash=generate_prompt_hash("latest")
         )
         handler = ImageGenerationHandler(self.api.db, PromptTracker(self.api.db))
+        self.addCleanup(close_handler, self, handler)
         handler.link_image_to_prompt(
             str(path),
             {"id": prompt_id, "text": "latest", "fallback": True},
diff --git a/tests/test_review_outcome.py b/tests/test_review_outcome.py
index b24a524..e83e77b 100644
--- a/tests/test_review_outcome.py
+++ b/tests/test_review_outcome.py
@@ -38,6 +38,7 @@ except ImportError:  # discovered with tests/ as the top-level directory
         write_png,
     )
 
+from tests.background_stops import close_handler
 from utils.hashing import generate_prompt_hash
 from utils.image_monitor import ImageGenerationHandler
 from utils.prompt_tracker import PromptTracker
@@ -299,6 +300,7 @@ class TestQueueSelfHeals(OutcomeTestCase):
 class TestMonitorRule(OutcomeTestCase):
     def _handler(self):
         handler = ImageGenerationHandler(self.api.db, PromptTracker(self.api.db))
+        self.addCleanup(close_handler, self, handler)
         handler.review_recorder = self.api.record_review_file
         return handler
 
diff --git a/tests/test_run_attribution.py b/tests/test_run_attribution.py
index 5ec53c6..ce3c60c 100644
--- a/tests/test_run_attribution.py
+++ b/tests/test_run_attribution.py
@@ -11,6 +11,7 @@ from unittest import mock
 
 from database.run_attribution import stored_run_prompt
 from tests import test_execution_history_database as history_tests
+from tests.background_stops import close_handler
 from tests.test_api_admin import AdminAPITestCase
 from tests.test_execution_context_database import snapshot
 from tests.test_prompt_attribution import issue_graph, llm_text_graph, make_tracker
@@ -151,6 +152,7 @@ class TestStoredRunPrompt(RecordedRuns, unittest.TestCase):
         prompt_id = self.save(LLM_TEXT)
         self.record_run(self.db, self.output, [("sub", "img_00001_.png")], [LLM_TEXT])
         handler = ImageGenerationHandler(self.db, make_tracker(self.db))
+        self.addCleanup(close_handler, self, handler)
         linked = []
         handler.link_image_to_prompt = lambda path, prompt, meta: linked.append(
             prompt["id"]
@@ -332,7 +334,7 @@ class TestMonitorHistoryRecheck(RecordedRuns, unittest.TestCase):
         self.handler = ImageGenerationHandler(self.db, make_tracker(self.db))
         self.handler.processing_delay = 0
         self.handler.settle_interval = 0.01
-        self.addCleanup(self.handler.shutdown)
+        self.addCleanup(close_handler, self, self.handler)
         self.linked = []
         self.handler.link_image_to_prompt = lambda path, prompt, meta: (
             self.linked.append((os.path.basename(path), prompt["id"]))
@@ -650,7 +652,7 @@ class TestLinkedOutputRoot(RecordedRuns, unittest.TestCase):
         handler = ImageGenerationHandler(db, make_tracker(db))
         handler.processing_delay = 0
         handler.settle_interval = 0.01
-        self.addCleanup(handler.shutdown)
+        self.addCleanup(close_handler, self, handler)
         linked = []
         handler.link_image_to_prompt = lambda path, prompt, meta: linked.append(
             prompt["id"]
diff --git a/tests/test_thumbnail_auto.py b/tests/test_thumbnail_auto.py
index d21677e..20ed0a5 100644
--- a/tests/test_thumbnail_auto.py
+++ b/tests/test_thumbnail_auto.py
@@ -32,6 +32,7 @@ from PIL import Image  # noqa: E402
 
 import py.api.images as images_module  # noqa: E402
 import py.api.thumbnail_auto as auto  # noqa: E402
+from tests.background_stops import close_handler, stop_monitor  # noqa: E402
 from py.api.jobs import THUMBNAILS_JOB_KIND  # noqa: E402
 
 SERVE = "/prompt_manager/images/serve/"
@@ -980,6 +981,7 @@ class TestMonitorQueuesThumbnails(AutoThumbnailCase):
         from utils.image_monitor import ImageGenerationHandler
 
         handler = ImageGenerationHandler(self.api.db, unittest.mock.MagicMock())
+        self.addCleanup(close_handler, self, handler)
         handler.processing_delay = 0
         handler.settle_interval = 0
         return handler
@@ -1022,7 +1024,7 @@ class TestMonitorQueuesThumbnails(AutoThumbnailCase):
             monitor.set_thumbnail_queue(None)
             self.assertIsNone(monitor.handler.thumbnail_queue)
         finally:
-            monitor.stop_monitoring()
+            stop_monitor(self, monitor)
 
 
 class TestScanHandsOffThumbnails(AutoThumbnailCase):
diff --git a/tests/test_usage_tracking.py b/tests/test_usage_tracking.py
index 11c7282..f4a9354 100644
--- a/tests/test_usage_tracking.py
+++ b/tests/test_usage_tracking.py
@@ -16,6 +16,7 @@ import uuid
 
 sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
 
+from tests.background_stops import stop_tracker  # noqa: E402
 from database.operations import PromptDatabase
 from prompt_manager_base import PromptManagerBase
 from utils.hashing import generate_prompt_hash
@@ -596,6 +597,7 @@ class TestNodeRoles(DbTestCase):
 class TestTrackerQueueFlag(unittest.TestCase):
     def setUp(self):
         self.tracker = PromptTracker(mock.Mock())
+        self.addCleanup(stop_tracker, self, self.tracker)
 
     def test_push_to_queue_false_keeps_the_batch_queue_empty(self):
         self.tracker.set_current_prompt("a cat", {"prompt_id": 1}, push_to_queue=False)
diff --git a/utils/image_monitor.py b/utils/image_monitor.py
index 773af07..d887186 100644
--- a/utils/image_monitor.py
+++ b/utils/image_monitor.py
@@ -70,6 +70,11 @@ MAX_AWAITING_HISTORY = 1000
 AWAIT_HISTORY_SECONDS = 3600
 # ``schedule`` snapshot meaning "history-only re-check" (not a new image)
 HISTORY_ONLY = object()
+# How long a stop waits for the image worker, and for the watchdog observer
+# after its stop (#302). Every wait before the image in hand is interrupted
+# at once, so a bound is reached only while one image is still being linked.
+WORKER_JOIN_SECONDS = 5.0
+OBSERVER_JOIN_SECONDS = 5.0
 
 
 class ImageGenerationHandler(FileSystemEventHandler):
@@ -143,6 +148,11 @@ class ImageGenerationHandler(FileSystemEventHandler):
         self._history_due: "OrderedDict[str, None]" = OrderedDict()
         self._awaiting_lock = threading.Lock()
         self._sealed_subscribed = False
+        # Set by ``close``: no new work, no new worker, ever (#302).
+        self._closed = False
+        # Workers a stop signalled that had not ended yet: every later stop
+        # waits for them again, so it never reports True too early.
+        self._finishing: List[threading.Thread] = []
 
     def on_created(self, event):
         """Handle filesystem creation events.
@@ -157,6 +167,10 @@ class ImageGenerationHandler(FileSystemEventHandler):
         Args:
             event: FileSystemEvent object containing event details
         """
+        # Closed: return before any log or tracker lock, so watchdog's
+        # ``observer.stop()`` never waits on this dispatch.
+        if self._closed:
+            return
         if event.is_directory or not self.is_image_file(event.src_path):
             return
         self.logger.info(f"New image detected: {event.src_path}")
@@ -180,9 +194,12 @@ class ImageGenerationHandler(FileSystemEventHandler):
         and once its size has stopped changing.
 
         Returns:
-            False when the path is already pending or the pending set is full
+            False when the path is already pending, the pending set is full or
+            the handler is closed
         """
         with self._pending_lock:
+            if self._closed:
+                return False
             if image_path in self._pending:
                 self.logger.debug(f"Already pending, not rescheduled: {image_path}")
                 return False
@@ -203,12 +220,19 @@ class ImageGenerationHandler(FileSystemEventHandler):
         with self._pending_lock:
             return len(self._pending)
 
-    def shutdown(self) -> None:
-        """Stop the worker thread and drop every image still waiting.
+    def shutdown(self, timeout: float = WORKER_JOIN_SECONDS) -> bool:
+        """Stop the worker thread, drop every image still waiting, and wait
+        for the worker within ``timeout`` seconds.
 
-        The worker wakes from any delay or settle wait, finishes nothing more
-        and exits; the next ``schedule`` starts a fresh worker with its own
-        queue. Safe to call repeatedly and before anything was scheduled.
+        The worker wakes from any delay or settle wait, finishes at most the
+        image in hand and exits; the next ``schedule`` starts a fresh worker
+        with its own queue (use ``close`` for a final stop). Safe to call
+        repeatedly and before anything was scheduled.
+
+        Returns:
+            True when no worker is left running. False when the worker is
+            still finishing its image after ``timeout`` (a warning is
+            logged), or when called on the worker itself (it only signals).
         """
         with self._awaiting_lock:
             self._awaiting.clear()
@@ -218,9 +242,40 @@ class ImageGenerationHandler(FileSystemEventHandler):
             worker, self._worker = self._worker, None
             work, self._work = self._work, queue.Queue()
             stop, self._stop = self._stop, threading.Event()
+            if worker is not None:
+                self._finishing.append(worker)
+            finishing = [w for w in self._finishing if w.is_alive()]
+            self._finishing = finishing
         stop.set()
         if worker is not None and worker.is_alive():
             work.put(None)  # sentinel: wake a worker idle on an empty queue
+        if threading.current_thread() in finishing:
+            self.logger.debug("shutdown called on the image worker itself")
+            return False
+        deadline = time.monotonic() + timeout
+        for thread in finishing:
+            thread.join(max(0.0, deadline - time.monotonic()))
+        with self._pending_lock:
+            self._finishing = [w for w in self._finishing if w.is_alive()]
+            still_running = bool(self._finishing)
+        if still_running:
+            self.logger.warning(
+                f"image worker still running after {timeout} s; "
+                "it stops after the image in hand"
+            )
+            return False
+        return True
+
+    def close(self, timeout: float = WORKER_JOIN_SECONDS) -> bool:
+        """Final stop: ``shutdown`` and refuse every later ``schedule``.
+
+        After ``close`` no worker starts again, not even from a sealed run's
+        history re-check on the history writer's thread. Returns what
+        ``shutdown`` returns.
+        """
+        with self._pending_lock:
+            self._closed = True
+        return self.shutdown(timeout)
 
     def _ensure_worker(self) -> None:
         """Start the single daemon worker thread if it isn't running.
@@ -521,7 +576,12 @@ class ImageGenerationHandler(FileSystemEventHandler):
             self._awaiting.popitem(last=False)
 
     def _await_history(self, image_path: str) -> None:
-        """Re-check ``image_path`` once, history only, when its run is sealed."""
+        """Re-check ``image_path`` once, history only, when its run is sealed.
+
+        A closed handler re-checks nothing.
+        """
+        if self._closed:
+            return
         if not self._sealed_subscribed:
             subscribe_outputs_sealed(self._on_outputs_sealed)
             self._sealed_subscribed = True
@@ -570,10 +630,19 @@ class ImageGenerationHandler(FileSystemEventHandler):
             self._schedule_recheck(image_path)
 
     def _schedule_recheck(self, image_path: str) -> None:
-        """Schedule the history-only re-check, or keep it due for later."""
+        """Schedule the history-only re-check, or keep it due for later.
+
+        A closed handler drops it.
+        """
+        if self._closed:
+            return
         if self.schedule(image_path, HISTORY_ONLY):
             return
         with self._awaiting_lock:
+            # ``close`` sets the flag before ``shutdown`` clears this set, so
+            # a close that raced the refusal above is seen here.
+            if self._closed:
+                return
             self._history_due.pop(image_path, None)
             self._history_due[image_path] = None
             while len(self._history_due) > MAX_AWAITING_HISTORY:
@@ -872,6 +941,9 @@ class ImageMonitor:
         self.observer = None
         self.handler = None
         self.monitored_directories = []
+        # (observer, handler) pairs a stop left running: the next stop waits
+        # for them again instead of reporting True.
+        self._unfinished: List[Tuple[Any, Any]] = []
         self.logger = get_logger("prompt_manager.image_monitor")
         self.review_recorder: Optional[Callable[[str], str]] = None
         self.thumbnail_queue: Optional[Callable[[str], str]] = None
@@ -999,29 +1071,69 @@ class ImageMonitor:
         """Whether a filesystem observer is running."""
         return self.observer is not None
 
-    def stop_monitoring(self):
-        """Stop the image monitoring system.
+    def stop_monitoring(self, timeout: float = OBSERVER_JOIN_SECONDS) -> bool:
+        """Stop the image monitoring system within one ``timeout`` deadline.
 
-        Cleanly shuts down the filesystem watcher and clears all monitoring state.
-        This method should be called before program exit to ensure proper cleanup.
-        Safe to call when monitoring never started.
+        Closes the handler first (its worker is joined and its dispatch
+        returns at once), then stops the watchdog observer and joins it.
+        watchdog's ``observer.stop()`` joins its emitters without a limit;
+        it counts against the deadline but is not bounded here. A part an
+        earlier call left running is waited for again. Safe to call when
+        monitoring never started and more than once.
+
+        Returns:
+            True when every worker and observer it stopped has ended.
         """
+        deadline = time.monotonic() + timeout
         observer, self.observer = self.observer, None
         handler, self.handler = self.handler, None
         self.monitored_directories = []
+        pairs, self._unfinished = self._unfinished, []
+        if observer is not None:
+            pairs.append((observer, handler))
+        if not pairs:
+            return True
+
+        def remaining() -> float:
+            return max(0.0, deadline - time.monotonic())
+
+        for pair_observer, pair_handler in pairs:
+            handler_ok = self._close_handler(pair_handler, remaining())
+            observer_ok = self._stop_observer(pair_observer, remaining())
+            if not observer_ok:
+                self.logger.warning(
+                    f"watchdog observer still running after {timeout} s"
+                )
+            if not (handler_ok and observer_ok):
+                self._unfinished.append(
+                    (
+                        None if observer_ok else pair_observer,
+                        None if handler_ok else pair_handler,
+                    )
+                )
+        self.logger.debug("Image monitoring stopped")
+        return not self._unfinished
+
+    def _close_handler(self, handler, timeout: float) -> bool:
+        if handler is None:
+            return True
+        try:
+            return handler.close(timeout)
+        except Exception as e:
+            self.logger.warning(f"Error while stopping the image worker: {e}")
+            return False
+
+    def _stop_observer(self, observer, timeout: float) -> bool:
+        """``observer.stop()`` (safe to repeat), then a bounded join."""
         if observer is None:
-            return
+            return True
         try:
             observer.stop()
-            observer.join()
+            observer.join(timeout)
         except Exception as e:
             self.logger.warning(f"Error while stopping image monitoring: {e}")
-        if handler is not None:
-            try:
-                handler.shutdown()
-            except Exception as e:
-                self.logger.warning(f"Error while stopping the image worker: {e}")
-        self.logger.debug("Image monitoring stopped")
+            return False
+        return not observer.is_alive()
 
     def detect_comfyui_output_dirs(self) -> list:
         """Auto-detect ComfyUI output directories.
diff --git a/utils/prompt_tracker.py b/utils/prompt_tracker.py
index fcc1c21..67f7c79 100644
--- a/utils/prompt_tracker.py
+++ b/utils/prompt_tracker.py
@@ -44,6 +44,9 @@ except ImportError:
     from utils.hashing import generate_prompt_hash
     from utils.logging_config import get_logger
 
+# How long ``PromptTracker.shutdown`` waits for the cleanup thread (#301).
+TRACKER_JOIN_SECONDS = 2.0
+
 
 class PromptTracker:
     """Thread-safe tracking of current prompt executions.
@@ -92,9 +95,12 @@ class PromptTracker:
             self.cleanup_interval = 300  # 5 minutes
             self.prompt_timeout = 600  # 10 minutes
 
-        # Start cleanup thread
+        # Start cleanup thread; ``shutdown`` sets ``_stop`` to end it.
+        self._stop = threading.Event()
         self.cleanup_thread = threading.Thread(
-            target=self._cleanup_expired_prompts, daemon=True
+            target=self._cleanup_expired_prompts,
+            name="PromptManagerPromptCleanup",
+            daemon=True,
         )
         self.cleanup_thread.start()
         self.logger.debug("PromptTracker initialization completed")
@@ -464,9 +470,10 @@ class PromptTracker:
 
         Runs continuously as a daemon thread, periodically removing expired
         prompt contexts from the global tracking dictionary. This prevents
-        memory leaks from accumulating old prompt data.
+        memory leaks from accumulating old prompt data. Every wait ends at
+        once when ``shutdown`` sets the stop event.
         """
-        while True:
+        while not self._stop.is_set():
             try:
                 current_time = time.time()
                 expired_ids = []
@@ -497,11 +504,37 @@ class PromptTracker:
                     if pruned:
                         self.logger.debug(f"Pruned {pruned} expired queue entries")
 
-                time.sleep(self.cleanup_interval)
+                if self._stop.wait(self.cleanup_interval):
+                    break
 
             except Exception as e:
                 self.logger.error(f"Error in cleanup thread: {e}")
-                time.sleep(60)  # Wait a minute before retrying
+                if self._stop.wait(60):  # Wait a minute before retrying
+                    break
+
+    def shutdown(self, timeout: float = TRACKER_JOIN_SECONDS) -> bool:
+        """Stop the cleanup thread and wait for it within ``timeout`` seconds.
+
+        Returns True when the thread has ended (or never existed). The tracker
+        keeps working afterwards; only the background pruning of expired
+        entries stops. Safe to call more than once. Called on the cleanup
+        thread itself it only signals and returns False.
+        """
+        stop = getattr(self, "_stop", None)
+        thread = getattr(self, "cleanup_thread", None)
+        if stop is None or thread is None:
+            return True  # built without __init__: no thread was started
+        stop.set()
+        if thread is threading.current_thread():
+            self.logger.debug("shutdown called on the prompt cleanup thread")
+            return False
+        thread.join(timeout)
+        if thread.is_alive():
+            self.logger.warning(
+                f"prompt cleanup thread still running after {timeout} s"
+            )
+            return False
+        return True
 
     def get_active_prompts(self) -> Dict[str, Dict[str, Any]]:
         """