diff --git a/nanobot/channels/websocket/runtime.py b/nanobot/channels/websocket/runtime.py
index 92f5f12fe..7e54209ef 100644
--- a/nanobot/channels/websocket/runtime.py
+++ b/nanobot/channels/websocket/runtime.py
@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import asyncio
+import errno
 import ipaddress
 import json
 import socket
@@ -538,14 +539,32 @@ class WebSocketChannel(BaseChannel):
     # -- Server lifecycle and connection ingress ---------------------------
 
     @staticmethod
-    def _listener_is_serving(server: Server) -> bool:
+    def _socket_is_accepting(sock: socket.socket) -> bool:
+        """Return whether a bound socket still advertises a listen capability.
+
+        ``SO_ACCEPTCONN`` is not portable: macOS/BSD raise ``OSError`` with
+        ``ENOPROTOOPT`` ("Protocol not available") for this option even on a
+        perfectly healthy listening socket. Treating that as "not serving"
+        makes the listener look permanently degraded, so the caller retries
+        forever and the channel never reaches a ready state. When the option
+        is unavailable we fall back to the file-descriptor liveness check.
+        """
+        if sock.fileno() < 0:
+            return False
+        try:
+            return bool(sock.getsockopt(socket.SOL_SOCKET, socket.SO_ACCEPTCONN))
+        except OSError as exc:
+            if exc.errno in (errno.ENOPROTOOPT, errno.EOPNOTSUPP, errno.EINVAL):
+                return True
+            raise
+
+    @classmethod
+    def _listener_is_serving(cls, server: Server) -> bool:
         """Return whether every bound socket still has a live listen capability."""
         try:
             sockets = server.sockets
             return bool(sockets) and server.is_serving() and all(
-                sock.fileno() >= 0
-                and bool(sock.getsockopt(socket.SOL_SOCKET, socket.SO_ACCEPTCONN))
-                for sock in sockets
+                cls._socket_is_accepting(sock) for sock in sockets
             )
         except OSError:
             return False
diff --git a/tests/channels/test_websocket_listener_health.py b/tests/channels/test_websocket_listener_health.py
new file mode 100644
index 000000000..22b85e9c7
--- /dev/null
+++ b/tests/channels/test_websocket_listener_health.py
@@ -0,0 +1,86 @@
+"""Regression tests for WebSocket listener health probing portability."""
+
+from __future__ import annotations
+
+import errno
+import socket
+from typing import Any
+
+import pytest
+
+from nanobot.channels.websocket.runtime import WebSocketChannel
+
+
+class _StubSocket:
+    """Minimal socket stand-in: real sockets forbid attribute patching."""
+
+    def __init__(self, *, fileno: int, error: OSError | None = None, value: int = 1):
+        self._fileno = fileno
+        self._error = error
+        self._value = value
+
+    def fileno(self) -> int:
+        return self._fileno
+
+    def getsockopt(self, *_args: Any, **_kwargs: Any) -> int:
+        if self._error is not None:
+            raise self._error
+        return self._value
+
+
+@pytest.fixture
+def listening_socket() -> socket.socket:
+    sock = socket.socket()
+    sock.bind(("127.0.0.1", 0))
+    sock.listen(1)
+    yield sock
+    sock.close()
+
+
+def test_real_listening_socket_is_accepting(listening_socket: socket.socket) -> None:
+    """A genuinely listening socket must never be reported as degraded.
+
+    On macOS/BSD this exercises the ``ENOPROTOOPT`` fallback path; on Linux it
+    exercises the native ``SO_ACCEPTCONN`` path. Both must agree.
+    """
+    assert WebSocketChannel._socket_is_accepting(listening_socket) is True
+
+
+def test_closed_socket_is_not_accepting() -> None:
+    sock = socket.socket()
+    sock.bind(("127.0.0.1", 0))
+    sock.listen(1)
+    sock.close()
+
+    assert WebSocketChannel._socket_is_accepting(sock) is False
+
+
+@pytest.mark.parametrize(
+    "unsupported_errno",
+    [errno.ENOPROTOOPT, errno.EOPNOTSUPP, errno.EINVAL],
+)
+def test_unsupported_sockopt_falls_back_to_fd_liveness(unsupported_errno: int) -> None:
+    """macOS/BSD reject ``SO_ACCEPTCONN`` even on healthy listeners.
+
+    Treating that rejection as "not serving" made the listener look permanently
+    degraded, so the channel retried forever and never became ready.
+    """
+    sock = _StubSocket(fileno=3, error=OSError(unsupported_errno, "Protocol not available"))
+
+    assert WebSocketChannel._socket_is_accepting(sock) is True
+
+
+def test_unexpected_oserror_propagates() -> None:
+    sock = _StubSocket(fileno=3, error=OSError(errno.EBADF, "Bad file descriptor"))
+
+    with pytest.raises(OSError) as excinfo:
+        WebSocketChannel._socket_is_accepting(sock)
+
+    assert excinfo.value.errno == errno.EBADF
+
+
+def test_unsupported_sockopt_still_rejects_dead_fd() -> None:
+    """The portability fallback must not mask an already-closed listener."""
+    sock = _StubSocket(fileno=-1, error=OSError(errno.ENOPROTOOPT, "Protocol not available"))
+
+    assert WebSocketChannel._socket_is_accepting(sock) is False