diff --git a/src/protocol.test.ts b/src/protocol.test.ts
index 06c2673..7735cb9 100644
--- a/src/protocol.test.ts
+++ b/src/protocol.test.ts
@@ -1,5 +1,5 @@
 import { describe, it, expect } from 'vitest';
-import { parseCommand } from './protocol.js';
+import { parseCommand, serializeResponse, successResponse } from './protocol.js';
 
 // Helper to create command JSON string
 const cmd = (obj: object) => JSON.stringify(obj);
@@ -1412,6 +1412,28 @@ describe('parseCommand', () => {
     });
   });
 
+  describe('serializeResponse - lone surrogate handling', () => {
+    it('should serialize response with lone surrogate to valid JSON', () => {
+      const response = successResponse('1', {
+        snapshot: 'button "test \uD800 click"',
+      });
+      const json = serializeResponse(response);
+      expect(() => JSON.parse(json)).not.toThrow();
+      const parsed = JSON.parse(json);
+      expect(parsed.data.snapshot).toContain('\uFFFD');
+      expect(parsed.data.snapshot).not.toMatch(/[\uD800-\uDFFF]/);
+    });
+
+    it('should preserve valid emoji characters', () => {
+      const response = successResponse('1', {
+        snapshot: 'button "😀 Click"',
+      });
+      const json = serializeResponse(response);
+      const parsed = JSON.parse(json);
+      expect(parsed.data.snapshot).toContain('😀');
+    });
+  });
+
   describe('invalid commands', () => {
     it('should reject unknown action', () => {
       const result = parseCommand(cmd({ id: '1', action: 'unknown' }));
diff --git a/src/protocol.ts b/src/protocol.ts
index 4b4200a..785d576 100644
--- a/src/protocol.ts
+++ b/src/protocol.ts
@@ -1149,8 +1149,12 @@ export function errorResponse(id: string, error: string): Response {
 }
 
 /**
- * Serialize a response to JSON string
+ * Serialize a response to JSON string.
+ * Replaces lone Unicode surrogates with U+FFFD to prevent
+ * serde_json parsing errors on the Rust side.
  */
 export function serializeResponse(response: Response): string {
-  return JSON.stringify(response);
+  return JSON.stringify(response, (_key, value) =>
+    typeof value === 'string' && !value.isWellFormed() ? value.toWellFormed() : value
+  );
 }
diff --git a/tsconfig.json b/tsconfig.json
index 93aa062..ff14e31 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -1,10 +1,10 @@
 {
   "compilerOptions": {
-    "target": "ES2022",
+    "target": "ES2024",
     "module": "NodeNext",
     "moduleResolution": "NodeNext",
     "lib": [
-      "ES2022"
+      "ES2024"
     ],
     "outDir": "./dist",
     "rootDir": "./src",