feat: render RTT history chart per connection in Connectivity section

hbd/server/templates/plugins.html

@@ -445,8 +445,12 @@
         </div>`;
 
         if (data.connections && data.connections.length) {
-          html += `<div class="info-thresholds-title">Connectivity</div>
+          html += `<div class="info-thresholds-title">Connectivity</div>`;
-            <table class="data-table"><thead><tr>
+          for (const c of data.connections) {
+            html += `<div class="info-note">${escHtml(c.family)} &middot; ${escHtml(c.addr || '—')} RTT</div>
+              <div id="rtt-chart-${hostname}-${escHtml(c.family)}" style="margin-bottom:8px;"></div>`;
+          }
+          html += `<table class="data-table"><thead><tr>
               <th>Family</th><th>Address</th><th>State</th>
               <th class="num">RTT</th><th>Last Change</th><th>Last Packet</th>
             </tr></thead><tbody>`;
@@ -495,6 +499,15 @@
         }
 
         el.innerHTML = html;
+
+        if (data.connections && data.connections.length) {
+          const rttThresholds = (data.thresholds || []).find(t => t.metric === 'rtt') || null;
+          for (const c of data.connections) {
+            fetchRttHistory(hostname, c.family)
+              .then(samples => renderRttChart(hostname, c.family, samples, rttThresholds))
+              .catch(() => {});
+          }
+        }
       }
 
       async function fetchHostGlance(hostname) {
@@ -899,6 +912,35 @@
         });
       }
 
+      async function fetchRttHistory(hostname, family) {
+        const plugin = `rtt_${family.toLowerCase()}`;
+        const r = await fetch(`/api/0/hosts/${encodeURIComponent(hostname)}/plugins/${plugin}?limit=100`);
+        if (!r.ok) return [];
+        const json = await r.json();
+        return json.samples || [];
+      }
+
+      function renderRttChart(hostname, family, samples, rttThresholds) {
+        const pts = samples
+          .filter(s => s.data.rtt != null && s.data.rtt > 0)
+          .map(s => ({ t: s.timestamp, v: s.data.rtt }));
+
+        renderTimeSeriesChart(`rtt-chart-${hostname}-${family}`, pts, {
+          yDomain: 'auto',
+          clipId: `rtt-clip-${hostname}-${family}`,
+          unitSuffix: ' ms',
+          colorFor: (latest) => {
+            if (rttThresholds?.critical != null && latest > rttThresholds.critical) {
+              return { stroke: '#e53935', fill: '#ffcdd2' };
+            }
+            if (rttThresholds?.warning != null && latest > rttThresholds.warning) {
+              return { stroke: '#fb8c00', fill: '#ffe0b2' };
+            }
+            return { stroke: '#1976d2', fill: '#bbdefb' };
+          },
+        });
+      }
+
       function renderCpuTable(hostname, d) {
         const KEYS = [
           ['cpu_percent',      'CPU Usage',         'bar'],