Fix overlay insertion index and batch annotation updates

darwin/mapkit_flutter/Sources/mapkit_flutter/Annotations/AnnotationController.swift

@@ -86,9 +86,15 @@ extension MapKitViewHost {
     }
 
     func annotationsToAdd(_ annotations: [PlatformAnnotation]) {
-        for annotation in annotations {
-            addAnnotation(FlutterAnnotation(fromPlatform: annotation))
+        let toAdd = annotations.map(FlutterAnnotation.init(fromPlatform:))
+        let stale = toAdd.compactMap { self.annotationsById.removeValue(forKey: $0.id) }
+        if !stale.isEmpty {
+            self.mapView.removeAnnotations(stale)
         }
+        for annotation in toAdd {
+            self.annotationsById[annotation.id] = annotation
+        }
+        self.mapView.addAnnotations(toAdd)
     }
 
     func annotationsToChange(_ annotations: [PlatformAnnotation]) {
@@ -107,8 +113,9 @@ extension MapKitViewHost {
     }
 
     func annotationsToRemove(_ annotationIds: [String]) {
-        for annotationId in annotationIds {
-            removeAnnotation(id: annotationId)
+        let toRemove = annotationIds.compactMap { self.annotationsById.removeValue(forKey: $0) }
+        if !toRemove.isEmpty {
+            self.mapView.removeAnnotations(toRemove)
         }
     }
 

darwin/mapkit_flutter/Sources/mapkit_flutter/Overlays/FlutterOverlay.swift

@@ -15,20 +15,22 @@ protocol FlutterOverlay: MKOverlay {
 
 extension MKMapView {
     /// Adds an overlay, using `zIndex` as an ordering hint within its level:
-    /// the overlay lands after every existing Flutter overlay whose zIndex is
-    /// `<=` its own, so equal indices preserve insertion order. The insertion
-    /// index is clamped to the level's array bounds.
+    /// the overlay lands directly before the first Flutter overlay whose
+    /// zIndex is greater than its own, so equal indices preserve insertion
+    /// order. Non-Flutter peers (tile overlays) carry no zIndex and never
+    /// shift the position; with no higher-zIndex peer the overlay is appended
+    /// on top of the level.
     func addFlutterOverlay(_ overlay: any FlutterOverlay) {
         let level = overlay.overlayLevel
         let peers = self.overlays(in: level)
-        let index = peers
-            .compactMap { $0 as? any FlutterOverlay }
-            .filter { $0.zIndex <= overlay.zIndex }
-            .count
-        if index >= peers.count {
-            addOverlay(overlay, level: level)
-        } else {
+        let index = peers.firstIndex { peer in
+            guard let flutterPeer = peer as? any FlutterOverlay else { return false }
+            return flutterPeer.zIndex > overlay.zIndex
+        }
+        if let index {
             insertOverlay(overlay, at: index, level: level)
+        } else {
+            addOverlay(overlay, level: level)
         }
     }