webui: use partial status polling

firmware/esp32/overland-controller/overland-controller.ino

@@ -240,6 +240,22 @@ input{width:100%;border:1px solid var(--line);border-radius:12px;padding:12px;ba
 <script>
 const API_BASE="/api/v1";
 function api(path){return API_BASE+path;}
+
+const STATUS_FIELDS_OVERVIEW="battery,temps,relays,vehicle,network,alarms,system";
+
+function isConfigTabActive(){
+  return $("configPage")?.classList.contains("active") || false;
+}
+
+function statusUrl(){
+  const needsFullStatus=isConfigTabActive() || !window.lastStatus?.config;
+  return needsFullStatus ? api("/status") : api("/status?fields="+STATUS_FIELDS_OVERVIEW);
+}
+
+function mergeStatus(previous,next){
+  if(!previous) return next;
+  return Object.assign({},previous,next);
+}
 const $=id=>document.getElementById(id);
 function fmt(n,d=1){return typeof n==="number"?n.toFixed(d):"--"}
 function temp(v){return typeof v==="number"?fmt(v,1)+"°F":"Offline"}
@@ -332,6 +348,7 @@ async function relay(id,on){
   await load();
 }
 function render(data){
+  data=mergeStatus(window.lastStatus,data);
   window.lastStatus=data;
   $("conn").textContent="Live";
   $("conn").className="pill good";
@@ -562,7 +579,7 @@ function renderConfigControls(data){
 }
 
 async function saveRelayConfig(){
-  const r=await fetch(api("/status"),{cache:"no-store"});
+  const r=await fetch(api("/status?fields=config"),{cache:"no-store"});
   const data=await r.json();
   const relays=data.config?.relays||[];
 
@@ -587,7 +604,7 @@ async function saveRelayConfig(){
 }
 
 async function saveTempConfig(){
-  const r=await fetch(api("/status"),{cache:"no-store"});
+  const r=await fetch(api("/status?fields=config"),{cache:"no-store"});
   const data=await r.json();
   const temps=data.config?.temperature_sensors||[];
 
@@ -649,7 +666,7 @@ async function connectWifi(){
 }
 async function load(){
   try{
-    const r=await fetch(api("/status"),{cache:"no-store"});
+    const r=await fetch(statusUrl(),{cache:"no-store"});
     render(await r.json());
   }catch(e){
     $("conn").textContent="Offline";

tests/test_http_api_contract.py

@@ -300,3 +300,14 @@ def test_status_endpoint_supports_field_selection_and_cache_headers():
     assert 'server.header("If-Modified-Since")' in source
     assert 'server.send(304)' in source
     assert 'server.collectHeaders(statusCacheHeaders, 2)' in source
+
+
+def test_embedded_webui_uses_partial_status_for_overview_polling():
+    source = firmware_source()
+
+    assert 'const STATUS_FIELDS_OVERVIEW="battery,temps,relays,vehicle,network,alarms,system";' in source
+    assert 'function statusUrl()' in source
+    assert 'api("/status?fields="+STATUS_FIELDS_OVERVIEW)' in source
+    assert 'fetch(statusUrl(),{cache:"no-store"})' in source
+    assert 'function mergeStatus(previous,next)' in source
+    assert 'api("/status?fields=config")' in source