fix(tooling): surface non-executable tool-use warnings

src/backends/native/agent.test.ts

@@ -270,6 +270,36 @@ describe('NativeAgent tool loop', () => {
     expect(mockClient.chat).toHaveBeenCalledTimes(3);
   });
 
+  it('surfaces warning when model emits textual tool_use block without structured tool calls', async () => {
+    const mockClient: ModelClient = {
+      chat: vi.fn().mockResolvedValue({
+        content: 'Let me read the full email to evaluate legitimacy:{"type":"tool_use","id":"call_123","name":"gmail_read","input":{"id":"abc"}}',
+        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('read latest email');
+    expect(response).toContain('Tool call was emitted as plain text and was not executed.');
+    expect(response).toContain('Tool: gmail_read (id: call_123)');
+    expect(response).toContain('"type":"tool_use"');
+
+    const history = agent.getHistory();
+    expect(history[history.length - 1]).toEqual({ role: 'assistant', content: response });
+  });
+
   it('works without tools (backward compatible)', async () => {
     const mockClient: ModelClient = {
       chat: vi.fn().mockResolvedValue({