fix: stop synthetic rtt_* keys from masking real plugin-data checks

host.plugin_data now always holds rtt_ipv4/rtt_ipv6 history after the
first heartbeat, which broke two pre-existing behaviors that assumed
plugin_data reflects only real client-collected data:

- The request_update ACK gate in handle_datagram() never fired again
  after a host's first heartbeat, so stale OS/agent-version info was
  never refreshed after a reconnect (only a client restart fixed it).
- plugin_data.clear() on every UP transition wiped rtt_* history too,
  so a flaky host could never accumulate a useful RTT graph.

Add _is_rtt_key()/_has_real_plugin_data() helpers so both spots treat
rtt_* keys as synthetic: the gate now looks only at real plugin data,
and the recovery clear only drops real plugin keys, preserving RTT
history across reconnects.

Also fixes two pre-existing E127 continuation-indent flake8 issues in
tests/test_udp_rtt_history.py.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DEimzMv4Q5EjFg3hoiZ69T

tests/test_udp_rtt_history.py

@@ -1,4 +1,6 @@
 """Tests for RTT history capture in udp.py's handle_datagram."""
+import time
+
 from hbd.common.proto import dicttos
 from hbd.server import hbdclass
 from hbd.server.udp import handle_datagram, parse_message
@@ -32,7 +34,7 @@ def _base_ctx():
 def test_handle_datagram_records_rtt_history_for_new_connection():
     hbdclass.Host.hosts.pop("rtt-hist-host", None)
     handle_datagram(_htb("rtt-hist-host", rtt=42.5), ("127.0.0.1", 50000),
-                     _FakeTransport(), _base_ctx())
+                    _FakeTransport(), _base_ctx())
 
     host = hbdclass.Host.hosts["rtt-hist-host"]
     samples = host.plugin_data.get("rtt_ipv4")
@@ -58,7 +60,64 @@ def test_handle_datagram_appends_rtt_history_across_heartbeats():
 def test_handle_datagram_skips_rtt_history_when_rtt_missing():
     hbdclass.Host.hosts.pop("rtt-hist-host3", None)
     handle_datagram(_htb("rtt-hist-host3", rtt=None), ("127.0.0.1", 50000),
-                     _FakeTransport(), _base_ctx())
+                    _FakeTransport(), _base_ctx())
 
     host = hbdclass.Host.hosts["rtt-hist-host3"]
     assert "rtt_ipv4" not in host.plugin_data
+
+
+def test_request_update_fires_on_recovery_even_with_rtt_history():
+    """Regression for Finding 1: rtt_* keys must not permanently disable the
+    request_update gate. A connection recovering from a non-UP state must
+    still be asked to resend real plugin data, even though rtt_ipv4 already
+    holds samples from before the drop.
+    """
+    hbdclass.Host.hosts.pop("rtt-hist-host4", None)
+    transport = _FakeTransport()
+    ctx = _base_ctx()
+
+    # First heartbeat: brand-new host, no plugin data at all yet.
+    handle_datagram(_htb("rtt-hist-host4", rtt=15.0), ("127.0.0.1", 50000), transport, ctx)
+    host = hbdclass.Host.hosts["rtt-hist-host4"]
+    assert host.plugin_data.get("rtt_ipv4")  # rtt history now non-empty
+
+    # Simulate a recovery: connection was dropped (e.g. OVERDUE->UP after a
+    # missed heartbeat) and is about to come back UP on the next heartbeat.
+    conn = host.connections["IPv4"]
+    conn.state = hbdclass.Connection.DOWN
+
+    transport.sent.clear()
+    handle_datagram(_htb("rtt-hist-host4", rtt=16.0), ("127.0.0.1", 50000), transport, ctx)
+
+    ack_data, _ = transport.sent[0]
+    ack = parse_message(ack_data)
+    assert ack.get("request_update")
+
+
+def test_recovery_clears_real_plugin_data_but_preserves_rtt_history():
+    """Regression for Finding 2: host.plugin_data.clear() on recovery must
+    wipe real client-collected plugin data while leaving rtt_* history
+    samples intact.
+    """
+    hbdclass.Host.hosts.pop("rtt-hist-host5", None)
+    transport = _FakeTransport()
+    ctx = _base_ctx()
+
+    for rtt in (10.0, 11.0, 12.0):
+        handle_datagram(_htb("rtt-hist-host5", rtt=rtt), ("127.0.0.1", 50000), transport, ctx)
+
+    host = hbdclass.Host.hosts["rtt-hist-host5"]
+    assert len(host.plugin_data["rtt_ipv4"]) == 3
+
+    # Simulate a drop, and pretend the client had previously sent real
+    # plugin data (collected before the connection went down).
+    conn = host.connections["IPv4"]
+    conn.state = hbdclass.Connection.DOWN
+    host.add_plugin_data("os_info", {"os": "linux"}, timestamp=time.time())
+    assert "os_info" in host.plugin_data
+
+    # Recovery heartbeat.
+    handle_datagram(_htb("rtt-hist-host5", rtt=13.0), ("127.0.0.1", 50000), transport, ctx)
+
+    assert "os_info" not in host.plugin_data
+    assert len(host.plugin_data["rtt_ipv4"]) == 4