docs(cursor): clarify optional capture metadata and rendering scope

flutter/lib/desktop/pages/remote_page.dart

@@ -1116,6 +1116,8 @@ class _ImagePaintState extends State<ImagePaint> {
             if (!isWeb && isViewScaled() && !zoomCursor.value && peerDpr > 0) {
               return (isWindows ? dpr : 1.0) / peerDpr;
             }
+            // Density metadata is optional. Keep the legacy path for hosts that
+            // omit it so capture-backend upgrades are not a client prerequisite.
             var cursorScale = 1.0;
             if (isWindows) {
               // debug win10

flutter/lib/models/model.dart

@@ -2850,7 +2850,8 @@ class CanvasModel with ChangeNotifier {
   }
 }
 
-// data for cursor
+// Scale the host's bitmap and hotspot together. Incorrect source geometry
+// must be fixed in host capture, independently of the client's sizing policy.
 class CursorData {
   final String peerId;
   final String id;
@@ -2858,7 +2859,7 @@ class CursorData {
   // Borrowed from CursorModel/PredefinedCursor, which own its lifetime.
   // The plugin clones the handle before starting asynchronous encoding.
   final ui.Image nativeImage;
-  // Zero preserves sizing for peers that predate cursor density metadata.
+  // Zero preserves legacy sizing for capture backends without density metadata.
   final double pixelRatio;
   double scale;
   Uint8List? data;

libs/base/protos/message.proto

@@ -316,7 +316,7 @@ message CursorData {
   int32 width = 4;
   int32 height = 5;
   bytes colors = 6;
-  // Physical bitmap pixels per remote logical pixel; 0 means an older sender.
+  // Physical bitmap pixels per remote logical pixel; 0 means unknown density.
   double scale = 7;
 }