fix: add MCP result validation, improve agent error handling and state management

- Add `_extract_mcp_content_text()` helper in naliia_tools.py to safely
  extract text from MCP results, preventing IndexError on empty content
- Replace all direct `result.content[0].text` accesses with safe helper
- Improve customer identification with preservation of existing state
- Add proper JSON parsing with fallback and error handling
- Simplify webhook state management (use agent's checkpointer internally)
- Update system prompt to remove check_mcp_connection tool reference
- Fix tests to use async mocks and correct expected values

tests/test_webhook.py

@@ -1,4 +1,5 @@
 import pytest
+from unittest.mock import AsyncMock
 from types import SimpleNamespace
 from httpx import ASGITransport, AsyncClient
 from naliiabotapi.main import app
@@ -12,27 +13,21 @@ class TestWebhookChatBot:
     async def tests_webhook_success(self, send_message_payload):
         """Test that the webhook endpoint returns a successful response.
 
-        Se crea un `mock_agent` con `invoke` mockeado y se inyecta
+        Se crea un `mock_agent` con `ainvoke` mockeado y se inyecta
         mediante `app.dependency_overrides` antes de realizar la petición.
         """
-        # Crear mock del agente y su invoke
         mock_agent = SimpleNamespace()
+        mock_agent.ainvoke = AsyncMock(
+            return_value={"messages": [SimpleNamespace(content="Respuesta mock")]}
+        )
 
-        def mock_invoke(state, config=None):
-            return {"messages": [SimpleNamespace(content="Respuesta mock")]}
-
-        mock_agent.invoke = mock_invoke
-
-        # Sobrescribir la dependencia del agente en la app
         app.dependency_overrides[get_agent] = lambda: mock_agent
 
         async with AsyncClient(
-                transport=ASGITransport(app=app),
-                base_url="http://localhost:8010"
+            transport=ASGITransport(app=app), base_url="http://localhost:8010"
         ) as client:
             response = await client.post("/webhook", json=send_message_payload)
 
-        # Limpiar override para no afectar a otros tests
         app.dependency_overrides.pop(get_agent, None)
 
         assert response.status_code == 200