fix(native-agent): recover textual tool_use JSON calls

src/backends/native/agent.test.ts

@@ -337,6 +337,44 @@ describe('NativeAgent tool loop', () => {
     expect(history[history.length - 1]).toEqual({ role: 'assistant', content: response });
   });
 
+  it('recovers and executes valid textual tool_use JSON for registered tools', async () => {
+    let callCount = 0;
+    const mockClient: ModelClient = {
+      chat: vi.fn().mockImplementation(() => {
+        callCount++;
+        if (callCount === 1) {
+          return {
+            content: 'Running tool now: {"type":"tool_use","id":"call_123","name":"test_echo","input":{"text":"hello"}}',
+            stopReason: 'end_turn',
+            usage: { inputTokens: 10, outputTokens: 5 },
+          };
+        }
+
+        return {
+          content: 'The tool returned: hello',
+          stopReason: 'end_turn',
+          usage: { inputTokens: 10, outputTokens: 5 },
+        };
+      }),
+    };
+
+    const registry = new ToolRegistry();
+    registry.register(echoTool);
+    const hooks = new HookEngine({ confirm: [], log: [], silent: [] });
+    const executor = new ToolExecutor(registry, hooks);
+
+    const agent = new NativeAgent({
+      modelClient: mockClient,
+      systemPrompt: 'You are helpful.',
+      toolRegistry: registry,
+      toolExecutor: executor,
+    });
+
+    const response = await agent.process('echo hello');
+    expect(response).toBe('The tool returned: hello');
+    expect(mockClient.chat).toHaveBeenCalledTimes(2);
+  });
+
   it('works without tools (backward compatible)', async () => {
     const mockClient: ModelClient = {
       chat: vi.fn().mockResolvedValue({