Reduce ADS-B map layout shift

static/css/adsb_dashboard.css

@@ -862,6 +862,9 @@ body {
     min-height: 300px;
     min-width: 0;
     overflow: hidden;
+    background: #08121c;
+    contain: layout paint;
+    overflow-anchor: none;
 }
 
 @media (min-width: 768px) {
@@ -880,17 +883,19 @@ body {
 
 .display-container {
     position: absolute;
-    top: 0;
-    left: 0;
-    right: 0;
-    bottom: 0;
+    inset: 0;
+    isolation: isolate;
+    contain: layout paint;
+    overflow-anchor: none;
 }
 
 #radarMap {
-    position: relative;
-    width: 100%;
-    height: 100%;
+    position: absolute;
+    inset: 0;
     display: block;
+    background: #08121c;
+    contain: layout paint;
+    overflow-anchor: none;
 }
 
 .map-crosshair-overlay {
@@ -904,6 +909,16 @@ body {
     --crosshair-x-end: 50%;
     --crosshair-y-end: 50%;
     --crosshair-duration: 1500ms;
+    contain: layout paint;
+    overflow-anchor: none;
+}
+
+#radarMap .leaflet-pane,
+#radarMap .leaflet-map-pane,
+#radarMap .leaflet-tile-pane,
+#radarMap .leaflet-overlay-pane,
+#radarMap .leaflet-tile {
+    overflow-anchor: none;
 }
 
 .map-crosshair-line {

templates/adsb_dashboard.html

@@ -453,6 +453,8 @@
         let panelSelectionFallbackTimer = null;
         let panelSelectionStageTimer = null;
         let mapCrosshairRequestId = 0;
+        let radarMapResizeObserver = null;
+        let radarMapSizeSyncFrame = null;
         // Watchlist - persisted to localStorage
         let watchlist = JSON.parse(localStorage.getItem('adsb_watchlist') || '[]');
 
@@ -1730,6 +1732,14 @@ ACARS: ${r.statistics.acarsMessages} messages`;
         window.addEventListener('pagehide', function() {
             if (eventSource) { eventSource.close(); eventSource = null; }
             if (gpsEventSource) { gpsEventSource.close(); gpsEventSource = null; }
+            if (radarMapResizeObserver) {
+                radarMapResizeObserver.disconnect();
+                radarMapResizeObserver = null;
+            }
+            if (radarMapSizeSyncFrame) {
+                cancelAnimationFrame(radarMapSizeSyncFrame);
+                radarMapSizeSyncFrame = null;
+            }
         });
 
         document.addEventListener('DOMContentLoaded', () => {
@@ -2134,6 +2144,29 @@ sudo make install</code>
             return layer;
         }
 
+        function scheduleRadarMapSizeSync(drawRings = false) {
+            if (!radarMap) return;
+            if (radarMapSizeSyncFrame) {
+                cancelAnimationFrame(radarMapSizeSyncFrame);
+            }
+            radarMapSizeSyncFrame = requestAnimationFrame(() => {
+                radarMapSizeSyncFrame = null;
+                if (!radarMap) return;
+                radarMap.invalidateSize({ pan: false, debounceMoveend: true });
+                if (drawRings) {
+                    drawRangeRings();
+                }
+            });
+        }
+
+        function attachRadarMapResizeObserver(container) {
+            if (!container || radarMapResizeObserver || typeof ResizeObserver === 'undefined') return;
+            radarMapResizeObserver = new ResizeObserver(() => {
+                scheduleRadarMapSizeSync(true);
+            });
+            radarMapResizeObserver.observe(container);
+        }
+
         async function initMap() {
             // Guard against double initialization (e.g. bfcache restore)
             const container = document.getElementById('radarMap');
@@ -2153,18 +2186,10 @@ sudo make install</code>
             // when internet map providers are slow or unreachable.
             const fallbackTiles = createFallbackGridLayer().addTo(radarMap);
 
-            // Draw range rings after map is ready
-            setTimeout(() => drawRangeRings(), 100);
-
-            // Fix map size on mobile after initialization
-            setTimeout(() => {
-                if (radarMap) radarMap.invalidateSize();
-            }, 200);
-
-            // Additional invalidateSize to ensure all tiles load
-            setTimeout(() => {
-                if (radarMap) radarMap.invalidateSize();
-            }, 500);
+            radarMap.whenReady(() => {
+                scheduleRadarMapSizeSync(true);
+            });
+            attachRadarMapResizeObserver(container);
 
             // Upgrade tiles via Settings in the background (non-blocking)
             if (typeof Settings !== 'undefined') {
@@ -2184,14 +2209,12 @@ sudo make install</code>
 
         // Handle window resize for map (especially important on mobile)
         window.addEventListener('resize', function() {
-            if (radarMap) radarMap.invalidateSize();
+            scheduleRadarMapSizeSync(true);
         });
 
         // Handle orientation changes for mobile devices
         window.addEventListener('orientationchange', function() {
-            setTimeout(() => {
-                if (radarMap) radarMap.invalidateSize();
-            }, 200);
+            scheduleRadarMapSizeSync(true);
         });
 
         // ============================================