fix(server): ignore datagrams that are not named HTB/PLG messages

A scanner's SIP INVITE on the public UDP port was parsed as a message without
a name and signed on a host called "unknown". Non-client datagrams are still
journaled but no longer create hosts or get an ACK.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

tests/test_udp_stray_datagrams.py

@@ -0,0 +1,40 @@
+"""Datagrams that are not heartbeat traffic (internet scanners) must not create hosts."""
+from hbd.common.proto import dicttos
+from hbd.server import hbdclass
+from hbd.server.udp import handle_datagram, parse_message
+
+
+class _FakeTransport:
+    sent = 0
+
+    def sendto(self, data, addr):
+        _FakeTransport.sent += 1
+
+
+def _ctx():
+    return {"config": {}, "hbdclass": hbdclass, "msg_to_websockets": None,
+            "DEBUG": 0, "verbose": False}
+
+
+def _handle(raw):
+    handle_datagram(parse_message(raw), ("192.0.2.9", 50000), _FakeTransport(), _ctx())
+
+
+def test_sip_invite_does_not_create_a_host():
+    hbdclass.Host.hosts.pop("unknown", None)
+    _handle(b"INVITE sip:10000@192.0.2.1:50003 SIP/2.0\r\nTo: <sip:10000@192.0.2.1>\r\n\r\n")
+    assert "unknown" not in hbdclass.Host.hosts
+
+
+def test_nameless_heartbeat_does_not_create_a_host_or_get_acked():
+    hbdclass.Host.hosts.pop("unknown", None)
+    _FakeTransport.sent = 0
+    _handle(dicttos("HTB", {"id": 0}))
+    assert "unknown" not in hbdclass.Host.hosts
+    assert _FakeTransport.sent == 0
+
+
+def test_named_heartbeat_still_creates_its_host():
+    hbdclass.Host.hosts.pop("stray-ok", None)
+    _handle(dicttos("HTB", {"name": "stray-ok", "id": 0}))
+    assert "stray-ok" in hbdclass.Host.hosts