feat(webui): live-update topology fan tiles without a page reload

Each fan tile carries data-fan / data-ceil / data-measured and a small
script polls /api/metrics/latest every 5s — the metrics collector's own
sampling period, served from memory with no extra BMC call — updating
each tile's spin rate, duty fill and tooltip in place. Polling faster
would only re-read identical numbers; sampling the BMC faster would
choke it under load. FanReading gains json tags for the endpoint.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019VHG21rgTUiR1G3qFHTVmN

audit/internal/webui/page_topo_diagram.go

@@ -694,21 +694,59 @@ func renderTopoFanRow(fans []schema.HardwareFanSensor, ceilByName, observedByNam
 				period, glyphSz, glyphSz) + topoFanGlyphPaths() + `</svg>`
 		}
 
-		fillBar := ""
+		measured := 0
+		fillH := 0.0
 		if duty >= 0 {
-			fillBar = fmt.Sprintf(`<div style="position:absolute;left:0;right:0;bottom:0;height:%.0f%%;background:%s;opacity:.55"></div>`, duty, stroke)
+			measured = 1
+			fillH = duty
 		}
+		fillBar := fmt.Sprintf(`<div class="topo-fan-fill" style="position:absolute;left:0;right:0;bottom:0;height:%.0f%%;background:%s;opacity:.55;transition:height .8s linear"></div>`, fillH, stroke)
 
-		fmt.Fprintf(&b, `<div title="%s" onclick="openComponentDetail('fan')" `+
+		fmt.Fprintf(&b, `<div class="topo-fan-tile" data-fan="%s" data-ceil="%d" data-measured="%d" title="%s" onclick="openComponentDetail('fan')" `+
 			`style="position:relative;overflow:hidden;width:%dpx;height:%dpx;display:flex;align-items:center;justify-content:center;`+
 			`border-radius:5px;background:var(--surface-2);border:1px solid %s;color:%s;cursor:pointer">`+
 			`%s<span style="position:relative;display:flex">%s</span></div>`,
-			html.EscapeString(title), side, side, stroke, text, fillBar, glyph)
+			html.EscapeString(name), int(ceil), measured, html.EscapeString(title),
+			side, side, stroke, text, fillBar, glyph)
 	}
 	b.WriteString(`</div>`)
+	b.WriteString(topoFanLiveScript())
 	return b.String()
 }
 
+// topoFanLiveScript polls the already-collected live-metrics snapshot
+// (/api/metrics/latest — served from memory, no BMC call) every 5s and
+// updates each fan tile's spin rate, duty fill and tooltip in place. 5s is
+// the metrics collector's own sampling period, so polling faster would only
+// re-read identical numbers; the endpoint is a mutex read + small JSON, so
+// this is cheap even with many viewers.
+func topoFanLiveScript() string {
+	return `<script>(function(){
+  var tiles=document.querySelectorAll('.topo-fan-tile');
+  if(!tiles.length)return;
+  function period(rpm){var lo=1000,hi=13000,slow=2.2,fast=0.35;
+    if(rpm<=lo)return slow;if(rpm>=hi)return fast;
+    return slow+(rpm-lo)/(hi-lo)*(fast-slow);}
+  function tick(){
+    fetch('/api/metrics/latest',{cache:'no-store'}).then(function(r){return r.json();}).then(function(m){
+      if(!m||!m.fans)return;
+      var by={};m.fans.forEach(function(f){by[f.name]=f.rpm;});
+      tiles.forEach(function(t){
+        var rpm=by[t.dataset.fan];if(rpm==null)return;
+        var ceil=parseFloat(t.dataset.ceil)||0;
+        var svg=t.querySelector('.topo-fan-spin');
+        if(svg&&rpm>0)svg.style.animationDuration=period(rpm).toFixed(2)+'s';
+        var meas=t.dataset.measured==='1'&&ceil>0;
+        var duty=meas?Math.max(0,Math.min(100,rpm/ceil*100)):-1;
+        if(meas){var fill=t.querySelector('.topo-fan-fill');if(fill)fill.style.height=duty.toFixed(0)+'%';}
+        t.title=t.dataset.fan+' · '+Math.round(rpm)+' RPM'+(meas?' · '+Math.round(duty)+'% duty (ceiling '+ceil+')':' · ceiling not measured — run Fan Ceiling Check');
+      });
+    }).catch(function(){});
+  }
+  setInterval(tick,5000);tick();
+})();</script>`
+}
+
 // fanSpinPeriodSec maps an absolute fan RPM to a CSS animation period (one
 // full turn of the glyph, in seconds). The real period would be 60/RPM — a
 // blur at any real fan speed — so it is compressed into a band the eye can

audit/internal/webui/page_topo_test.go

@@ -206,6 +206,13 @@ func TestTopoPageRendersCoolingFansAsFlexRow(t *testing.T) {
 	if !strings.Contains(body, "ceiling not measured") {
 		t.Fatalf("topo fan tooltip should note the ceiling is unmeasured: %s", body)
 	}
+	// Live-update: each tile is addressable and the poll script is present.
+	if n := strings.Count(body, `class="topo-fan-tile"`); n != 2 {
+		t.Fatalf("expected 2 addressable fan tiles, got %d", n)
+	}
+	if !strings.Contains(body, `data-fan="FAN1"`) || !strings.Contains(body, "/api/metrics/latest") {
+		t.Fatalf("topo fan row missing live-update wiring: %s", body)
+	}
 
 	// Component-detail fallback endpoint must resolve the "fan" type.
 	rec2 := httptest.NewRecorder()