diff --git a/pyproject.toml b/pyproject.toml
index 2e7ac44..8558433 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -22,6 +22,7 @@ dependencies = [
     "psutil>=5.9.0",
     "python-dotenv>=1.0.0",
     "sqlmodel>=0.0.16",
+    "scapy>=2.6.1",
 ]
 
 [project.optional-dependencies]
@@ -53,7 +54,6 @@ dev = [
     "psycopg2-binary>=2.9.11",
     "paho-mqtt>=2.1.0",
     "pymongo>=4.16.0",
-    "scapy>=2.6.1",
 ]
 
 [project.scripts]
@@ -62,7 +62,7 @@ decnet = "decnet.cli:app"
 [tool.pytest.ini_options]
 asyncio_mode = "auto"
 asyncio_debug = "true"
-addopts = "-m 'not fuzz and not live' -v -q -x -n logical"
+addopts = "-m 'not fuzz and not live' -v -q -x -n logical --dist loadscope"
 markers = [
     "fuzz: hypothesis-based fuzz tests (slow, run with -m fuzz or -m '' for all)",
     "live: live subprocess service tests (run with -m live)",
diff --git a/tests/api/conftest.py b/tests/api/conftest.py
index e0860d5..32aff91 100644
--- a/tests/api/conftest.py
+++ b/tests/api/conftest.py
@@ -12,6 +12,18 @@ from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_asyn
 from sqlalchemy.pool import StaticPool
 import os as _os
 
+
+def pytest_ignore_collect(collection_path, config):
+    """Skip test_schemathesis.py unless fuzz marker is selected.
+
+    Its module-level code starts a subprocess server and mutates
+    decnet.web.auth.SECRET_KEY, which poisons other test suites.
+    """
+    if collection_path.name == "test_schemathesis.py":
+        markexpr = config.getoption("markexpr", default="")
+        if "fuzz" not in markexpr:
+            return True
+
 # Must be set before any decnet import touches decnet.env
 os.environ["DECNET_JWT_SECRET"] = "test-secret-key-at-least-32-chars-long!!"
 os.environ["DECNET_ADMIN_PASSWORD"] = "test-password-123"
diff --git a/tests/live/test_health_live.py b/tests/live/test_health_live.py
index 398af86..275a352 100644
--- a/tests/live/test_health_live.py
+++ b/tests/live/test_health_live.py
@@ -97,7 +97,6 @@ async def token(live_client):
 
 
 @pytest.mark.live
-@pytest.mark.xdist_group("health_live")
 class TestHealthLive:
     """Live integration tests — real DB, real Docker check, real task state."""
 
diff --git a/tests/live/test_service_isolation_live.py b/tests/live/test_service_isolation_live.py
index be2f12e..d14824d 100644
--- a/tests/live/test_service_isolation_live.py
+++ b/tests/live/test_service_isolation_live.py
@@ -128,7 +128,6 @@ async def token(live_client):
 
 
 @pytest.mark.live
-@pytest.mark.xdist_group("service_isolation_live")
 class TestCollectorLiveIsolation:
     """Real collector behaviour against the actual Docker daemon."""
 
@@ -204,7 +203,6 @@ class TestCollectorLiveIsolation:
 
 
 @pytest.mark.live
-@pytest.mark.xdist_group("service_isolation_live")
 class TestIngesterLiveIsolation:
     """Real ingester against real DB and real filesystem."""
 
@@ -314,7 +312,6 @@ class TestIngesterLiveIsolation:
 
 
 @pytest.mark.live
-@pytest.mark.xdist_group("service_isolation_live")
 class TestAttackerWorkerLiveIsolation:
     """Real attacker worker against real DB."""
 
@@ -363,7 +360,6 @@ class TestAttackerWorkerLiveIsolation:
 
 
 @pytest.mark.live
-@pytest.mark.xdist_group("service_isolation_live")
 class TestSnifferLiveIsolation:
     """Real sniffer against the actual host network stack."""
 
@@ -400,7 +396,6 @@ class TestSnifferLiveIsolation:
 
 
 @pytest.mark.live
-@pytest.mark.xdist_group("service_isolation_live")
 class TestApiLifespanLiveIsolation:
     """Real API lifespan against real DB and real host state."""
 
@@ -447,7 +442,6 @@ class TestApiLifespanLiveIsolation:
 
 
 @pytest.mark.live
-@pytest.mark.xdist_group("service_isolation_live")
 class TestCascadeLiveIsolation:
     """Verify that real component failures do not cascade."""