View: resize if moved between outputs while fullscreen

river/View.zig

@@ -303,6 +303,13 @@ pub fn sendToOutput(self: *Self, destination_output: *Output) void {
         self.foreign_toplevel_handle.?.outputEnter(destination_output.wlr_output);
     }
 
+    const dimensions = destination_output.getEffectiveResolution();
+    self.pending.box = .{
+        .x = 0,
+        .y = 0,
+        .width = dimensions.width,
+        .height = dimensions.height,
+    };
     self.output = destination_output;
 }