fix: preserve chart history across reconnects, show gaps for missing data

Only wipe real (non-RTT) plugin data on an actual client reboot (boot
flag), not on every ordinary OVERDUE/DOWN -> UP recovery. A transient
network blip no longer erases CPU/memory/etc. history.

Also split the shared time-series chart into separate line/area segments
wherever the gap between samples is much larger than the typical spacing,
so missing data (host overdue, or history that simply hasn't accumulated
across a drop) renders as a visual gap instead of an interpolated line.

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

hbd/server/templates/plugins.html

@@ -847,16 +847,38 @@
         const yRange = yHigh - yLow || 1;
         const y = v => PAD.top + cH - ((v - yLow) / yRange) * cH;
 
-        // Build polyline points and filled area path
-        const linePoints = pts.map(p => `${x(p.t).toFixed(1)},${y(p.v).toFixed(1)}`).join(' ');
-        const areaPath = `M${x(pts[0].t).toFixed(1)},${(PAD.top + cH).toFixed(1)} ` +
-          pts.map(p => `L${x(p.t).toFixed(1)},${y(p.v).toFixed(1)}`).join(' ') +
-          ` L${x(pts[pts.length-1].t).toFixed(1)},${(PAD.top + cH).toFixed(1)} Z`;
-
         // Color based on latest value
         const latest = pts[pts.length - 1].v;
         const { stroke: strokeColor, fill: fillColor } = opts.colorFor(latest);
 
+        // Split into segments wherever the gap between consecutive samples is
+        // much larger than the typical spacing (e.g. the host was overdue/down
+        // for a while) — draw each segment separately so missing data reads as
+        // a visual gap instead of an interpolated line across dead time.
+        const deltas = [];
+        for (let i = 1; i < pts.length; i++) deltas.push(pts[i].t - pts[i - 1].t);
+        deltas.sort((a, b) => a - b);
+        const medianDelta = deltas[Math.floor(deltas.length / 2)];
+        const gapThreshold = medianDelta * 2.5;
+
+        const segments = [[pts[0]]];
+        for (let i = 1; i < pts.length; i++) {
+          if (pts[i].t - pts[i - 1].t > gapThreshold) segments.push([]);
+          segments[segments.length - 1].push(pts[i]);
+        }
+
+        let linePolylines = '';
+        let areaPaths = '';
+        for (const seg of segments) {
+          if (seg.length < 2) continue;
+          const segPoints = seg.map(p => `${x(p.t).toFixed(1)},${y(p.v).toFixed(1)}`).join(' ');
+          linePolylines += `<polyline points="${segPoints}" fill="none" stroke="${strokeColor}" stroke-width="1.5" stroke-linejoin="round"/>`;
+          const segArea = `M${x(seg[0].t).toFixed(1)},${(PAD.top + cH).toFixed(1)} ` +
+            seg.map(p => `L${x(p.t).toFixed(1)},${y(p.v).toFixed(1)}`).join(' ') +
+            ` L${x(seg[seg.length-1].t).toFixed(1)},${(PAD.top + cH).toFixed(1)} Z`;
+          areaPaths += `<path d="${segArea}" fill="${fillColor}" opacity="0.6"/>`;
+        }
+
         // Compute nice tick step for ~3-5 grid lines
         const rawStep = yRange / 4;
         const mag = Math.pow(10, Math.floor(Math.log10(rawStep || 1)));
@@ -890,8 +912,8 @@
           <line x1="${PAD.left}" y1="${PAD.top}" x2="${PAD.left}" y2="${PAD.top + cH}" stroke="#ccc" stroke-width="1"/>
           <line x1="${PAD.left}" y1="${PAD.top + cH}" x2="${PAD.left + cW}" y2="${PAD.top + cH}" stroke="#ccc" stroke-width="1"/>
           <g clip-path="url(#${opts.clipId})">
-            <path d="${areaPath}" fill="${fillColor}" opacity="0.6"/>
+            ${areaPaths}
-            <polyline points="${linePoints}" fill="none" stroke="${strokeColor}" stroke-width="1.5" stroke-linejoin="round"/>
+            ${linePolylines}
           </g>
           ${xLabels}
         </svg>`;

hbd/server/udp.py

@@ -521,9 +521,13 @@ def handle_datagram(msg: dict, addr, transport, ctx: dict):
         # Transition to UP and log/notify if appropriate
         lasts = conn.state
         d = conn.newstate(hbdcls.Connection.UP, now)
+        if boot:
             # On reboot, pre-boot plugin data and derived alerts are stale.
             # Cancel all plugin timers and wipe plugin state so timers restart
-        # cleanly from the first two post-boot samples.
+            # cleanly from the first two post-boot samples. An ordinary
+            # reconnect (no boot flag) doesn't invalidate the client's
+            # already-collected data, so it's left alone — this keeps chart
+            # history intact across a transient network blip.
             for pname in list(host.plugin_timers):
                 host.cancel_plugin_timer(pname)
             for pname in [k for k in host.plugin_data if not _is_rtt_key(k)]:

tests/test_udp_rtt_history.py

@@ -14,10 +14,12 @@ class _FakeTransport:
         self.sent.append((data, addr))
 
 
-def _htb(name, rtt=None, interval=0):
+def _htb(name, rtt=None, interval=0, boot=0):
     d = {"name": name, "interval": interval, "id": 0}
     if rtt is not None:
         d["rtt"] = rtt
+    if boot:
+        d["boot"] = boot
     return parse_message(dicttos("HTB", d))
 
 
@@ -94,10 +96,11 @@ def test_request_update_fires_on_recovery_even_with_rtt_history():
     assert ack.get("request_update")
 
 
-def test_recovery_clears_real_plugin_data_but_preserves_rtt_history():
+def test_ordinary_recovery_preserves_real_plugin_data_and_rtt_history():
-    """Regression for Finding 2: host.plugin_data.clear() on recovery must
+    """An ordinary reconnect (no boot flag) — e.g. OVERDUE->UP after a
-    wipe real client-collected plugin data while leaving rtt_* history
+    transient network blip — must NOT wipe already-collected real plugin
-    samples intact.
+    data (e.g. cpu_monitor, os_info) or rtt_* history. Only an actual
+    client reboot invalidates that data (see the boot-flag test below).
     """
     hbdclass.Host.hosts.pop("rtt-hist-host5", None)
     transport = _FakeTransport()
@@ -116,8 +119,35 @@ def test_recovery_clears_real_plugin_data_but_preserves_rtt_history():
     host.add_plugin_data("os_info", {"os": "linux"}, timestamp=time.time())
     assert "os_info" in host.plugin_data
 
-    # Recovery heartbeat.
+    # Ordinary recovery heartbeat — no boot flag.
     handle_datagram(_htb("rtt-hist-host5", rtt=13.0), ("127.0.0.1", 50000), transport, ctx)
 
+    assert "os_info" in host.plugin_data
+    assert len(host.plugin_data["rtt_ipv4"]) == 4
+
+
+def test_boot_recovery_clears_real_plugin_data_but_preserves_rtt_history():
+    """A recovery heartbeat carrying the boot flag (client process actually
+    restarted) must still wipe stale real plugin data, while rtt_* history
+    (still a valid measurement, unaffected by a client reboot) survives.
+    """
+    hbdclass.Host.hosts.pop("rtt-hist-host6", None)
+    transport = _FakeTransport()
+    ctx = _base_ctx()
+
+    for rtt in (10.0, 11.0, 12.0):
+        handle_datagram(_htb("rtt-hist-host6", rtt=rtt), ("127.0.0.1", 50000), transport, ctx)
+
+    host = hbdclass.Host.hosts["rtt-hist-host6"]
+    assert len(host.plugin_data["rtt_ipv4"]) == 3
+
+    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 with boot=1 — client process actually restarted.
+    handle_datagram(_htb("rtt-hist-host6", rtt=13.0, boot=1), ("127.0.0.1", 50000), transport, ctx)
+
     assert "os_info" not in host.plugin_data
     assert len(host.plugin_data["rtt_ipv4"]) == 4