fix: rewrite Google Maps traffic layer to avoid L-instance constructor error

Replace static import + createLayerComponent approach with dynamic import()
inside a useEffect, which ensures leaflet.gridlayer.googlemutant augments the
same L instance that's active at runtime. Add loading=async to Maps JS script.

Traffic is now toggled via a dedicated button (green when active) rather than
LayersControl, bypassing the react-leaflet layer lifecycle that caused the
constructor conflict.

drb-frontend/components/MapView.tsx

@@ -1,6 +1,6 @@
 "use client";
 
-import { useCallback, useEffect, useMemo, useState } from "react";
+import { useCallback, useEffect, useMemo, useRef, useState } from "react";
 import {
   FeatureGroup,
   LayersControl,
@@ -10,9 +10,7 @@ import {
   TileLayer,
   useMap,
 } from "react-leaflet";
-import { createLayerComponent } from "@react-leaflet/core";
 import L from "leaflet";
-import "leaflet.gridlayer.googlemutant";
 import type { CallRecord, IncidentRecord, NodeRecord } from "@/lib/types";
 
 // ── Leaflet icon fix ──────────────────────────────────────────────────────────
@@ -148,17 +146,53 @@ function computeGroups<T extends { id: string; lat: number; lng: number }>(
 }
 
 // ── Google Maps traffic layer via leaflet-google-mutant ───────────────────────
+// Uses dynamic import so the side-effect augments the same L instance at runtime,
+// avoiding the "GoogleMutant is not a constructor" error from static top-level imports.
+function GoogleTrafficManager({ enabled }: { enabled: boolean }) {
+  const map = useMap();
   // eslint-disable-next-line @typescript-eslint/no-explicit-any
-const GoogleTrafficOverlay = createLayerComponent<any, object>(
+  const layerRef = useRef<any>(null);
-  (_props, ctx) => {
+  const scriptLoadedRef = useRef(false);
-    // leaflet-google-mutant augments L.gridLayer after the side-effect import
+
+  useEffect(() => {
+    if (!enabled) {
+      if (layerRef.current) { map.removeLayer(layerRef.current); layerRef.current = null; }
+      return;
+    }
+
+    const key = process.env.NEXT_PUBLIC_GOOGLE_MAPS_API_KEY;
+    if (!key) return;
+
+    function mountLayer() {
+      import("leaflet.gridlayer.googlemutant").then(() => {
+        if (layerRef.current) return; // already mounted
         // eslint-disable-next-line @typescript-eslint/no-explicit-any
-    const instance = (L as any).gridLayer.googleMutant({ type: "roadmap" });
+        const layer = (L as any).gridLayer.googleMutant({ type: "roadmap" });
-    instance.addGoogleLayer("TrafficLayer");
+        layer.addGoogleLayer("TrafficLayer");
-    return { instance, context: ctx };
+        map.addLayer(layer);
-  },
+        layerRef.current = layer;
-  () => {}
+      });
-);
+    }
+
+    // eslint-disable-next-line @typescript-eslint/no-explicit-any
+    if ((window as any).google?.maps) {
+      mountLayer();
+    } else if (!scriptLoadedRef.current) {
+      scriptLoadedRef.current = true;
+      const script = document.createElement("script");
+      script.src = `https://maps.googleapis.com/maps/api/js?key=${key}&loading=async`;
+      script.async = true;
+      script.onload = mountLayer;
+      document.head.appendChild(script);
+    }
+
+    return () => {
+      if (layerRef.current) { map.removeLayer(layerRef.current); layerRef.current = null; }
+    };
+  }, [enabled, map]);
+
+  return null;
+}
 
 // ── MapRefCapture — exposes L.Map instance to parent ─────────────────────────
 function MapRefCapture({ onReady }: { onReady: (m: L.Map) => void }) {
@@ -357,20 +391,7 @@ export default function MapView({ nodes, activeCalls, incidents = [], lastUpdate
     return () => clearInterval(id);
   }, []);
 
-  // Load Google Maps JS API for leaflet-google-mutant traffic layer
+  const [trafficEnabled, setTrafficEnabled] = useState(false);
-  const [googleReady, setGoogleReady] = useState(false);
-  useEffect(() => {
-    const key = process.env.NEXT_PUBLIC_GOOGLE_MAPS_API_KEY;
-    if (!key) return;
-    // eslint-disable-next-line @typescript-eslint/no-explicit-any
-    if ((window as any).google?.maps) { setGoogleReady(true); return; }
-    if (document.querySelector('script[src*="maps.googleapis.com/maps/api/js"]')) return;
-    const script = document.createElement("script");
-    script.src = `https://maps.googleapis.com/maps/api/js?key=${key}`;
-    script.async = true;
-    script.onload = () => setGoogleReady(true);
-    document.head.appendChild(script);
-  }, []);
 
   // Live clock for TOC situational awareness
   useEffect(() => {
@@ -468,10 +489,8 @@ export default function MapView({ nodes, activeCalls, incidents = [], lastUpdate
             </FeatureGroup>
           </LayersControl.Overlay>
 
-          {/* Overlay: Traffic — Google Maps via leaflet-google-mutant */}
+          {/* Traffic managed outside LayersControl to avoid L-instance conflicts */}
-          <LayersControl.Overlay name="Traffic">
+          <GoogleTrafficManager enabled={trafficEnabled} />
-            {googleReady ? <GoogleTrafficOverlay /> : <FeatureGroup />}
-          </LayersControl.Overlay>
 
           {/* Overlay: Weather Radar — NEXRAD via Iowa Env Mesonet; key forces remount on refresh */}
           <LayersControl.Overlay name="Weather Radar">
@@ -504,6 +523,21 @@ export default function MapView({ nodes, activeCalls, incidents = [], lastUpdate
         </div>
       )}
 
+      {/* ── Traffic toggle ───────────────────────────────────────────────────── */}
+      {process.env.NEXT_PUBLIC_GOOGLE_MAPS_API_KEY && (
+        <button
+          onClick={() => setTrafficEnabled((v) => !v)}
+          title="Toggle traffic layer"
+          className={`absolute bottom-[6.5rem] right-3 z-[1001] w-8 h-8 border rounded text-xs font-bold leading-none transition-colors flex items-center justify-center select-none ${
+            trafficEnabled
+              ? "bg-green-700 border-green-500 text-white"
+              : "bg-gray-950/90 border-gray-700 text-gray-400 hover:bg-gray-800"
+          }`}
+        >
+          🚦
+        </button>
+      )}
+
       {/* ── Auto-fit button ──────────────────────────────────────────────────── */}
       {mapInstance && allPositions.length > 0 && (
         <button