diff --git a/Makefile b/Makefile
index 1b8ffa1..8c71e5b 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,6 @@
 PYTHON ?= uv run python
 UV_CACHE_DIR ?= .uv-cache
+PYTEST_FLAGS ?= -n auto
 OLLAMA_BASE_URL ?= http://localhost:11434/v1
 OLLAMA_MODEL ?= llama3.2:3b
 OLLAMA_DEMO_FLAGS ?=
@@ -27,7 +28,7 @@ help:
 		'  lint                      Run Ruff lint checks' \
 		'  format                    Run Ruff formatter' \
 		'  typecheck                 Run mypy' \
-		'  test                      Run pytest' \
+		'  test                      Run pytest in parallel when multiple cores are available' \
 		'  check                     Run lint, typecheck, and tests' \
 		'  dist-check                Smoke-test the installed pyro CLI and environment UX' \
 		'  pypi-publish              Build, validate, and upload the package to PyPI' \
@@ -76,7 +77,7 @@ typecheck:
 	uv run mypy
 
 test:
-	uv run pytest
+	uv run pytest $(PYTEST_FLAGS)
 
 check: lint typecheck test
 
diff --git a/pyproject.toml b/pyproject.toml
index 09f08ca..044f601 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -67,6 +67,7 @@ dev = [
     "pre-commit>=4.5.1",
     "pytest>=9.0.2",
     "pytest-cov>=7.0.0",
+    "pytest-xdist>=3.8.0",
     "ruff>=0.15.4",
 ]
 
diff --git a/src/pyro_mcp/vm_manager.py b/src/pyro_mcp/vm_manager.py
index eb90462..e25be5f 100644
--- a/src/pyro_mcp/vm_manager.py
+++ b/src/pyro_mcp/vm_manager.py
@@ -1589,6 +1589,23 @@ def _stop_process_group(pid: int, *, wait_seconds: int = 5) -> tuple[bool, bool]
     return True, True
 
 
+def _linux_process_state(pid: int) -> str | None:
+    stat_path = Path("/proc") / str(pid) / "stat"
+    try:
+        raw_stat = stat_path.read_text(encoding="utf-8", errors="replace").strip()
+    except OSError:
+        return None
+    if raw_stat == "":
+        return None
+    closing_paren = raw_stat.rfind(")")
+    if closing_paren == -1:
+        return None
+    suffix = raw_stat[closing_paren + 2 :]
+    if suffix == "":
+        return None
+    return suffix.split(" ", 1)[0]
+
+
 def _run_service_probe_command(
     cwd: Path,
     command: str,
@@ -1962,6 +1979,11 @@ def _ensure_no_symlink_parents(root: Path, target_path: Path, member_name: str)
 def _pid_is_running(pid: int | None) -> bool:
     if pid is None:
         return False
+    process_state = _linux_process_state(pid)
+    if process_state == "Z":
+        return False
+    if process_state is not None:
+        return True
     try:
         os.kill(pid, 0)
     except ProcessLookupError:
diff --git a/tests/test_runtime_network_check.py b/tests/test_runtime_network_check.py
index 35b5a87..0e26b5d 100644
--- a/tests/test_runtime_network_check.py
+++ b/tests/test_runtime_network_check.py
@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+import sys
+
 import pytest
 
 import pyro_mcp.runtime_network_check as runtime_network_check
@@ -43,6 +45,7 @@ def test_network_check_uses_network_enabled_manager(monkeypatch: pytest.MonkeyPa
 def test_network_check_main_fails_on_unsuccessful_command(
     monkeypatch: pytest.MonkeyPatch, capsys: pytest.CaptureFixture[str]
 ) -> None:
+    monkeypatch.setattr(sys, "argv", ["runtime-network-check"])
     monkeypatch.setattr(
         runtime_network_check,
         "run_network_check",
diff --git a/tests/test_vm_manager.py b/tests/test_vm_manager.py
index f8010d3..22e953c 100644
--- a/tests/test_vm_manager.py
+++ b/tests/test_vm_manager.py
@@ -2937,6 +2937,11 @@ def test_workspace_service_process_group_helpers(monkeypatch: pytest.MonkeyPatch
     assert kill_calls == [signal.SIGTERM, signal.SIGKILL]
 
 
+def test_pid_is_running_treats_zombies_as_stopped(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setattr(vm_manager_module, "_linux_process_state", lambda _pid: "Z")
+    assert vm_manager_module._pid_is_running(123) is False  # noqa: SLF001
+
+
 def test_workspace_service_probe_and_refresh_helpers(
     tmp_path: Path, monkeypatch: pytest.MonkeyPatch
 ) -> None:
diff --git a/tests/test_workspace_shells.py b/tests/test_workspace_shells.py
index 4f4f206..b0efcd9 100644
--- a/tests/test_workspace_shells.py
+++ b/tests/test_workspace_shells.py
@@ -154,6 +154,7 @@ def test_workspace_shells_write_and_signal_runtime_errors(
     tmp_path: Path,
     monkeypatch: pytest.MonkeyPatch,
 ) -> None:
+    real_killpg = os.killpg
     session = create_local_shell(
         workspace_id="workspace-6",
         shell_id="shell-6",
@@ -189,6 +190,7 @@ def test_workspace_shells_write_and_signal_runtime_errors(
         monkeypatch.setattr("pyro_mcp.workspace_shells.os.killpg", _raise_killpg)
         with pytest.raises(RuntimeError, match="not running"):
             session.send_signal("INT")
+        monkeypatch.setattr("pyro_mcp.workspace_shells.os.killpg", real_killpg)
     finally:
         try:
             session.close()
diff --git a/uv.lock b/uv.lock
index 9e194db..d688e08 100644
--- a/uv.lock
+++ b/uv.lock
@@ -275,6 +275,15 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/33/6b/e0547afaf41bf2c42e52430072fa5658766e3d65bd4b03a563d1b6336f57/distlib-0.4.0-py2.py3-none-any.whl", hash = "sha256:9659f7d87e46584a30b5780e43ac7a2143098441670ff0a49d5f9034c54a6c16", size = 469047, upload-time = "2025-07-17T16:51:58.613Z" },
 ]
 
+[[package]]
+name = "execnet"
+version = "2.1.2"
+source = { registry = "https://pypi.org/simple" }
+sdist = { url = "https://files.pythonhosted.org/packages/bf/89/780e11f9588d9e7128a3f87788354c7946a9cbb1401ad38a48c4db9a4f07/execnet-2.1.2.tar.gz", hash = "sha256:63d83bfdd9a23e35b9c6a3261412324f964c2ec8dcd8d3c6916ee9373e0befcd", size = 166622, upload-time = "2025-11-12T09:56:37.75Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/ab/84/02fc1827e8cdded4aa65baef11296a9bbe595c474f0d6d758af082d849fd/execnet-2.1.2-py3-none-any.whl", hash = "sha256:67fba928dd5a544b783f6056f449e5e3931a5c378b128bc18501f7ea79e296ec", size = 40708, upload-time = "2025-11-12T09:56:36.333Z" },
+]
+
 [[package]]
 name = "filelock"
 version = "3.25.0"
@@ -718,6 +727,7 @@ dev = [
     { name = "pre-commit" },
     { name = "pytest" },
     { name = "pytest-cov" },
+    { name = "pytest-xdist" },
     { name = "ruff" },
 ]
 
@@ -730,6 +740,7 @@ dev = [
     { name = "pre-commit", specifier = ">=4.5.1" },
     { name = "pytest", specifier = ">=9.0.2" },
     { name = "pytest-cov", specifier = ">=7.0.0" },
+    { name = "pytest-xdist", specifier = ">=3.8.0" },
     { name = "ruff", specifier = ">=0.15.4" },
 ]
 
@@ -763,6 +774,19 @@ wheels = [
     { url = "https://files.pythonhosted.org/packages/ee/49/1377b49de7d0c1ce41292161ea0f721913fa8722c19fb9c1e3aa0367eecb/pytest_cov-7.0.0-py3-none-any.whl", hash = "sha256:3b8e9558b16cc1479da72058bdecf8073661c7f57f7d3c5f22a1c23507f2d861", size = 22424, upload-time = "2025-09-09T10:57:00.695Z" },
 ]
 
+[[package]]
+name = "pytest-xdist"
+version = "3.8.0"
+source = { registry = "https://pypi.org/simple" }
+dependencies = [
+    { name = "execnet" },
+    { name = "pytest" },
+]
+sdist = { url = "https://files.pythonhosted.org/packages/78/b4/439b179d1ff526791eb921115fca8e44e596a13efeda518b9d845a619450/pytest_xdist-3.8.0.tar.gz", hash = "sha256:7e578125ec9bc6050861aa93f2d59f1d8d085595d6551c2c90b6f4fad8d3a9f1", size = 88069, upload-time = "2025-07-01T13:30:59.346Z" }
+wheels = [
+    { url = "https://files.pythonhosted.org/packages/ca/31/d4e37e9e550c2b92a9cbc2e4d0b7420a27224968580b5a447f420847c975/pytest_xdist-3.8.0-py3-none-any.whl", hash = "sha256:202ca578cfeb7370784a8c33d6d05bc6e13b4f25b5053c30a152269fd10f0b88", size = 46396, upload-time = "2025-07-01T13:30:56.632Z" },
+]
+
 [[package]]
 name = "python-discovery"
 version = "1.1.0"