diff --git a/pyproject.toml b/pyproject.toml
index f105810..9cb6265 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "hatchling.build"
 
 [project]
 name = "zmqruntime"
-version = "0.6.3"
+version = "0.6.4"
 description = "Generic ZMQ-based distributed execution framework"
 authors = [{name = "Tristan Simas", email = "tristan.simas@mail.mcgill.ca"}]
 license = {text = "MIT"}
@@ -26,7 +26,7 @@ keywords = ["zmq", "zeromq", "distributed", "execution", "rpc", "messaging"]
 
 dependencies = [
     "annotated-types>=0.7.0",
-    "metaclass-registry>=0.1.6",
+    "metaclass-registry>=0.4.0",
     "numpy>=1.24",
     "portalocker>=2.8.2",
     "pyzmq>=22.0",
diff --git a/src/zmqruntime/server.py b/src/zmqruntime/server.py
index db96e98..0289d7a 100644
--- a/src/zmqruntime/server.py
+++ b/src/zmqruntime/server.py
@@ -12,7 +12,6 @@
 from collections.abc import Callable, Mapping
 
 import zmq
-from metaclass_registry import AutoRegisterMeta
 from typing_extensions import Self
 
 from zmqruntime.config import TransportMode, ZMQConfig
@@ -38,17 +37,15 @@
 logger = logging.getLogger(__name__)
 
 
-class ZMQServer(ABC, metaclass=AutoRegisterMeta):
+class ZMQServer(ABC):
     """
     ABC for ZMQ servers - dual-channel pattern with ping/pong handshake.
 
-    Registry auto-created and stored as ZMQServer.__registry__.
-    Subclasses auto-register by setting _server_type class attribute.
+    ``_server_type`` is the runtime role a server reports in its pong. Several
+    server classes may serve one role, so servers are not registered by it.
     """
 
-    __registry_key__ = "_server_type"
-
-    _server_type: str | None = None  # Override in subclasses for registration
+    _server_type: str | None = None  # The runtime role reported in the pong
     _server_role = ServerRole.GENERIC
 
     @classmethod
diff --git a/src/zmqruntime/transport_modes.py b/src/zmqruntime/transport_modes.py
index 9b623b5..f70d611 100644
--- a/src/zmqruntime/transport_modes.py
+++ b/src/zmqruntime/transport_modes.py
@@ -588,6 +588,13 @@ def data_control_pair_is_available(
     @classmethod
     @contextmanager
     def private_endpoint(cls, config: ZMQConfig) -> Iterator[ZMQConfig]:
-        """A new socket directory, removed when the caller is done with it."""
-        with tempfile.TemporaryDirectory(prefix=f"{config.app_name}-") as directory:
+        """A new socket directory, removed when the caller is done with it.
+
+        The directory is created beneath ``config.socket_root()``, so the
+        length of its socket paths does not depend on ``TMPDIR``: a path
+        longer than ``zmq.IPC_PATH_MAX_LEN`` cannot be bound.
+        """
+        root = config.socket_root()
+        root.mkdir(parents=True, exist_ok=True)
+        with tempfile.TemporaryDirectory(prefix="private-", dir=root) as directory:
             yield replace(config, ipc_socket_dir=directory)
diff --git a/tests/test_transport.py b/tests/test_transport.py
index 5a35ba3..cd27c5c 100644
--- a/tests/test_transport.py
+++ b/tests/test_transport.py
@@ -195,6 +195,36 @@ def test_transport_mode_owns_ipc_socket_binding() -> None:
     assert endpoint_socket.random_bind_requests == []
 
 
+@pytest.mark.skipif(platform.system() == "Windows", reason="IPC is POSIX-only")
+def test_private_ipc_endpoint_lives_under_the_socket_root_not_tmpdir(
+    monkeypatch, tmp_path
+) -> None:
+    long_tmpdir = tmp_path / ("t" * 120)
+    long_tmpdir.mkdir()
+    monkeypatch.setenv("TMPDIR", str(long_tmpdir))
+    monkeypatch.setattr("tempfile.tempdir", None)
+    config = ZMQConfig(app_name=f"zmqruntime-test-{uuid.uuid4().hex[:8]}")
+    root = config.socket_root()
+    declaration = TransportMode.IPC.declaration
+
+    try:
+        with declaration.private_endpoint(config) as first:
+            with declaration.private_endpoint(config) as second:
+                first_dir = Path(first.ipc_socket_dir)
+                second_dir = Path(second.ipc_socket_dir)
+                assert first_dir != second_dir
+                assert first_dir.parent == second_dir.parent == root
+                assert first_dir.is_dir() and second_dir.is_dir()
+                socket_path = declaration.socket_path(65535, first)
+                assert socket_path.parent == first_dir
+                assert len(str(socket_path).encode()) <= zmq.IPC_PATH_MAX_LEN
+        assert not first_dir.exists() and not second_dir.exists()
+        assert list(long_tmpdir.iterdir()) == []
+    finally:
+        if root.exists():
+            root.rmdir()
+
+
 @pytest.mark.skipif(platform.system() == "Windows", reason="IPC is POSIX-only")
 def test_ipc_startup_lock_obeys_total_operation_deadline() -> None:
     config = ZMQConfig(