Replace focused text from Android source

WirelessTextSyncer.Windows.Tests/SyncMessageTests.cs

@@ -1,5 +1,6 @@
 using System.Text.Json;
 using WirelessTextSyncer.Windows.Models;
+using WirelessTextSyncer.Windows.Services;
 
 namespace WirelessTextSyncer.Windows.Tests;
 
@@ -28,4 +29,58 @@ public sealed class SyncMessageTests
         Assert.IsNotNull(message);
         Assert.AreEqual(SyncAction.Backspace, message.Action);
     }
+
+    [TestMethod]
+    public void DeserializeAndroidReplaceAllMessage()
+    {
+        var message = JsonSerializer.Deserialize<SyncMessage>(
+            """{"action":"replaceAll","text":"final text"}""",
+            new JsonSerializerOptions(JsonSerializerDefaults.Web));
+
+        Assert.IsNotNull(message);
+        Assert.AreEqual(SyncAction.ReplaceAll, message.Action);
+        Assert.AreEqual("final text", message.Text);
+    }
+
+    [TestMethod]
+    public void ReplaceAllUsesFocusedTextReplacement()
+    {
+        var keyboard = new RecordingKeyboardInjectionService();
+        var handler = new SyncMessageHandler(keyboard);
+
+        handler.Handle(new SyncMessage
+        {
+            Action = SyncAction.ReplaceAll,
+            Text = "final text"
+        });
+
+        CollectionAssert.AreEqual(
+            new[] { "replace:final text" },
+            keyboard.Calls);
+    }
+
+    private sealed class RecordingKeyboardInjectionService : IKeyboardInjectionService
+    {
+        public List<string> Calls { get; } = [];
+
+        public void InsertText(string text)
+        {
+            Calls.Add($"insert:{text}");
+        }
+
+        public void ReplaceFocusedText(string text)
+        {
+            Calls.Add($"replace:{text}");
+        }
+
+        public void Backspace()
+        {
+            Calls.Add("backspace");
+        }
+
+        public void Enter()
+        {
+            Calls.Add("enter");
+        }
+    }
 }