Planner: respuesta directa para saludos y preguntas simples

El planner ahora puede devolver direct_response en vez de un plan
cuando el mensaje no requiere herramientas (saludos, preguntas
generales, conversación casual).

- planner.py: prompt actualizado con formato direct_response
- engine.py: si planner devuelve string, emitir como texto y
  completar sin ejecutar steps

"hola" → "¡Hola! ¿En qué puedo ayudarte hoy?" (0 steps, 0 tools)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/orchestrator/engine.py

@@ -118,8 +118,54 @@ class OrchestratorEngine:
         planner_usage: dict[str, int] = {"input_tokens": 0, "output_tokens": 0}
         try:
             planner = self._create_agent(AgentRole.PLANNER)
-            plan_steps, planner_usage = await planner.plan(session)
-            task.plan = plan_steps
+            plan_result, planner_usage = await planner.plan(session)
+
+            # Direct response — no plan needed (saludo, pregunta simple)
+            if isinstance(plan_result, str):
+                logger.info("Planner returned direct response for task %s", task.task_id)
+                task.status = TaskStatus.COMPLETED
+                session.complete_task()
+
+                # Emit as text streaming for the frontend
+                await self.sse.emit(
+                    EventType.AGENT_DELTA,
+                    {"agent": "planner", "delta": plan_result, "step": 0},
+                    session_id=session.session_id,
+                )
+
+                cost_usd = (
+                    (planner_usage.get("input_tokens", 0) / 1_000_000) * settings.cost_per_1m_input
+                    + (planner_usage.get("output_tokens", 0) / 1_000_000) * settings.cost_per_1m_output
+                )
+
+                await self.sse.emit(
+                    EventType.EXECUTION_COMPLETED,
+                    {
+                        "session_id": session.session_id,
+                        "task_id": task.task_id,
+                        "steps_completed": 0,
+                        "steps_failed": [],
+                        "status": "completed",
+                        "usage": planner_usage,
+                        "total_cost_usd": round(cost_usd, 6),
+                    },
+                    session_id=session.session_id,
+                )
+
+                return {
+                    "session_id": session.session_id,
+                    "task_id": task.task_id,
+                    "content": plan_result,
+                    "steps_completed": 0,
+                    "steps_failed": [],
+                    "artifacts_count": 0,
+                    "review": "",
+                    "status": "completed",
+                    "usage": planner_usage,
+                    "total_cost_usd": round(cost_usd, 6),
+                }
+
+            task.plan = plan_result
             task.status = TaskStatus.EXECUTING
         except Exception as e:
             logger.error("Planning failed: %s", e)
@@ -134,7 +180,7 @@ class OrchestratorEngine:
 
         logger.info(
             "Plan created with %d steps for task %s",
-            len(plan_steps),
+            len(plan_result),
             task.task_id,
         )