Fix intermittent loss of options positions and realtime PnL on refresh.

Use stale-while-revalidate for positions API and UI, throttle sync calls, and avoid overwriting displayed PnL with null on transient failures.

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/instance/templates/embed_boot_scripts.html

@@ -1081,6 +1081,16 @@ function paintRealtimePnl(v){
         pnlEl.classList.toggle("pnl-neg", n < 0);
     });
 }
+let lastRealtimePnl = null;
+function updateRealtimePnl(v){
+    if(v != null && !Number.isNaN(Number(v))){
+        lastRealtimePnl = Number(v);
+        paintRealtimePnl(v);
+        return;
+    }
+    if(lastRealtimePnl != null) return;
+    paintRealtimePnl(v);
+}
 function sumOrdersFloatPnl(orders){
     if(!orders || !orders.length) return null;
     let total = 0, found = false;
@@ -1153,7 +1163,7 @@ function applyAccountSnapshot(data){
         setFundsFieldText("options-trading-usdc", `${Number(data.options_trading_usdc).toFixed(2)} USDC`);
     }
     if(typeof data.unrealized_pnl !== "undefined"){
-        paintRealtimePnl(data.unrealized_pnl);
+        updateRealtimePnl(data.unrealized_pnl);
     }
     if(typeof data.available_trading_usdt !== "undefined" && data.available_trading_usdt !== null){
         latestAvailableUsdt = Number(data.available_trading_usdt);