fix(preview): derive signals from OSM controls

scripts/lib/cesium-preview.js

@@ -482,6 +482,7 @@
       const state = { elapsedSeconds: 0, phase: "" };
       const entities = [];
       const nodes = new Map();
+      const countdownNodes = new WeakMap();
       const node = (name) => {
         if (nodes.has(name)) return nodes.get(name);
         let value = null;
@@ -496,6 +497,18 @@
         if (value) nodes.set(name, value);
         return value;
       };
+      const countdownNode = (model, name) => {
+        let modelNodes = countdownNodes.get(model);
+        if (!modelNodes) {
+          modelNodes = new Map();
+          countdownNodes.set(model, modelNodes);
+        }
+        if (modelNodes.has(name)) return modelNodes.get(name);
+        let value = null;
+        try { value = model.getNode(name); } catch (error) { /* model node table is still loading */ }
+        if (value) modelNodes.set(name, value);
+        return value;
+      };
       const update = (elapsedSeconds) => {
         Cesium.JulianDate.addSeconds(start, elapsedSeconds, phaseTime);
         let changed = false;
@@ -516,7 +529,7 @@
           for (let value = 0; value < 20; value += 1) {
             const name = `TrafficSignalDynamic_${signal.id}_countdown_${String(value).padStart(2, "0")}`;
             let countdown = null;
-            try { countdown = countdownModel.getNode(name); } catch (error) { /* model node table is still loading */ }
+            countdown = countdownNode(countdownModel, name);
             if (countdown && countdown.show !== (String(value).padStart(2, "0") === visibleCountdown)) {
               countdown.show = String(value).padStart(2, "0") === visibleCountdown;
               changed = true;
@@ -544,6 +557,13 @@
       // countdown must remain visibly periodic.
       const timer = setInterval(render, 250);
       render();
+      // Countdown GLBs may expose their node table a few frames after the
+      // model object exists. Re-apply the initial state once both models are
+      // ready so every hidden digit is explicitly hidden before the first
+      // user-visible frame.
+      for (const model of countdownModels.values()) {
+        if (model.readyPromise) model.readyPromise.then(() => update(0)).catch(() => {});
+      }
       return {
         entities, count: signals.length, dynamic, state, timer,
         set show(value) {