diff --git a/tests/docker/dirty_ttin_ttou/Dockerfile b/tests/docker/dirty_ttin_ttou/Dockerfile
index 7d6c66ae..0c6cd837 100644
--- a/tests/docker/dirty_ttin_ttou/Dockerfile
+++ b/tests/docker/dirty_ttin_ttou/Dockerfile
@@ -6,9 +6,11 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
 
 WORKDIR /app
 
-# Install gunicorn from source
+# Install gunicorn from source.  setproctitle is required so dirty-arbiter
+# and dirty-worker processes get distinguishable names that the tests use
+# to count workers via pgrep.
 COPY . /gunicorn-src/
-RUN pip install --no-cache-dir /gunicorn-src/
+RUN pip install --no-cache-dir /gunicorn-src/ setproctitle
 
 # Copy test app
 COPY tests/docker/dirty_ttin_ttou/app.py /app/
diff --git a/tests/docker/dirty_ttin_ttou/app.py b/tests/docker/dirty_ttin_ttou/app.py
index 0030e5b8..df77da8d 100644
--- a/tests/docker/dirty_ttin_ttou/app.py
+++ b/tests/docker/dirty_ttin_ttou/app.py
@@ -45,10 +45,14 @@ def app(environ, start_response):
         start_response('200 OK', [('Content-Type', 'text/plain')])
         return [b'OK']
 
+    # client.execute(app_path, action, *args, **kwargs) — action is the
+    # method name on the DirtyApp.  The original fixture passed the data
+    # dict where ``action`` belongs, which surfaced as a 500 from
+    # ``getattr(self, action)`` on the dirty worker.
     if path == '/unlimited':
         try:
             client = get_dirty_client()
-            result = client.execute('app:UnlimitedTask', {'test': 'data'})
+            result = client.execute('app:UnlimitedTask', 'process', {'test': 'data'})
             start_response('200 OK', [('Content-Type', 'application/json')])
             return [json.dumps(result).encode()]
         except Exception as e:
@@ -59,7 +63,7 @@ def app(environ, start_response):
     if path == '/limited':
         try:
             client = get_dirty_client()
-            result = client.execute('app:LimitedTask', {'test': 'data'})
+            result = client.execute('app:LimitedTask', 'process', {'test': 'data'})
             start_response('200 OK', [('Content-Type', 'application/json')])
             return [json.dumps(result).encode()]
         except Exception as e:
diff --git a/tests/docker/dirty_ttin_ttou/test_ttin_ttou_docker.py b/tests/docker/dirty_ttin_ttou/test_ttin_ttou_docker.py
index ca72c26d..f63305c9 100644
--- a/tests/docker/dirty_ttin_ttou/test_ttin_ttou_docker.py
+++ b/tests/docker/dirty_ttin_ttou/test_ttin_ttou_docker.py
@@ -21,7 +21,10 @@ pytestmark = [
 # Directory containing this test file
 TEST_DIR = Path(__file__).parent
 COMPOSE_FILE = TEST_DIR / "docker-compose.yml"
-BASE_URL = "http://localhost:18000"
+# Use 127.0.0.1 (not "localhost") so we always hit IPv4. Docker Desktop /
+# OrbStack on macOS map host ports to IPv4 only, and ``localhost`` resolves
+# to ``::1`` on this host, which yields connection-reset noise.
+BASE_URL = "http://127.0.0.1:18000"
 
 
 @pytest.fixture(scope="module")
@@ -100,6 +103,30 @@ def send_signal_to_dirty_arbiter(sig):
     )
 
 
+def wait_for_apps_ready(*paths, timeout=10):
+    """Poll the given app endpoints until each returns 200.
+
+    The dirty arbiter rebalances apps across workers asynchronously after
+    TTIN/TTOU signals.  Tests that care about app availability — rather
+    than worker counts — should call this between scaling and the request
+    so they don't race the rebalance.
+    """
+    deadline = time.time() + timeout
+    pending = list(paths)
+    while pending and time.time() < deadline:
+        for path in list(pending):
+            try:
+                resp = requests.get(f"{BASE_URL}{path}", timeout=2)
+                if resp.status_code == 200:
+                    pending.remove(path)
+            except requests.RequestException:
+                pass
+        if pending:
+            time.sleep(0.5)
+    if pending:
+        raise RuntimeError(f"Apps did not become ready: {pending}")
+
+
 class TestTTINSignal:
     """Test SIGTTIN increases dirty workers."""
 
@@ -159,14 +186,24 @@ class TestTTOUSignal:
 class TestUnlimitedApps:
     """Test apps with worker_count=None work correctly."""
 
-    def test_unlimited_app_works(self, docker_services):
+    @pytest.fixture(autouse=True)
+    def _ready(self, docker_services):
+        # The TTOU-spam test before this class may leave the arbiter at
+        # the floor (2 workers).  Bump the count back up so LimitedTask
+        # has spare capacity, then wait for both apps to be reachable.
+        for _ in range(2):
+            send_signal_to_dirty_arbiter("TTIN")
+            time.sleep(0.5)
+        wait_for_apps_ready("/unlimited", "/limited", timeout=30)
+
+    def test_unlimited_app_works(self):
         """UnlimitedTask should work."""
         resp = requests.get(f"{BASE_URL}/unlimited", timeout=10)
         assert resp.status_code == 200
         data = resp.json()
         assert data["task"] == "unlimited"
 
-    def test_limited_app_works(self, docker_services):
+    def test_limited_app_works(self):
         """LimitedTask should work."""
         resp = requests.get(f"{BASE_URL}/limited", timeout=10)
         assert resp.status_code == 200
diff --git a/tests/docker/per_app_allocation/README.md b/tests/docker/per_app_allocation/README.md
index bae552d7..91535227 100644
--- a/tests/docker/per_app_allocation/README.md
+++ b/tests/docker/per_app_allocation/README.md
@@ -58,5 +58,5 @@ pytest test_per_app_e2e.py::TestPerAppAllocation::test_config_limited_app_uses_o
 
 ## Notes
 
-- Tests run on port 8001 to avoid conflicts with the existing dirty_arbiter tests on 8000
+- Tests run on port 28001 to avoid conflicts with the existing dirty_arbiter tests on 8000 and with macOS Docker alternatives that often reserve port 8001 (e.g., OrbStack's vcom-tunnel)
 - The container uses a keep-alive wrapper to allow testing worker crash scenarios
diff --git a/tests/docker/per_app_allocation/docker-compose.yml b/tests/docker/per_app_allocation/docker-compose.yml
index 19aaf7c8..a389cd0b 100644
--- a/tests/docker/per_app_allocation/docker-compose.yml
+++ b/tests/docker/per_app_allocation/docker-compose.yml
@@ -4,7 +4,7 @@ services:
       context: ../../..
       dockerfile: tests/docker/per_app_allocation/Dockerfile
     ports:
-      - "8001:8000"
+      - "28001:8000"
     healthcheck:
       test: ["CMD", "curl", "-f", "http://localhost:8000/status"]
       interval: 1s
diff --git a/tests/docker/per_app_allocation/test_per_app_e2e.py b/tests/docker/per_app_allocation/test_per_app_e2e.py
index 1abcb1b3..e1c34472 100644
--- a/tests/docker/per_app_allocation/test_per_app_e2e.py
+++ b/tests/docker/per_app_allocation/test_per_app_e2e.py
@@ -39,7 +39,7 @@ class DockerContainer:
         self.name = name
         self.build = build
         self.container_id = None
-        self.base_url = "http://127.0.0.1:8001"
+        self.base_url = "http://127.0.0.1:28001"
 
     def __enter__(self):
         # Build if requested
@@ -64,7 +64,7 @@ class DockerContainer:
             [
                 "docker", "run", "-d",
                 "--name", self.name,
-                "-p", "8001:8000",
+                "-p", "28001:8000",
                 "per_app_allocation-gunicorn",
                 "sh", "-c",
                 "gunicorn app:application -c gunicorn_conf.py & "