Emitir plan como bloque tool_use visible en el frontend

El plan del planner se emite como tool_use(name="plan") + tool_result
con los steps formateados. El frontend lo renderiza como un bloque
colapsable de herramienta con el plan de ejecución.

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

src/orchestrator/engine.py

@@ -201,6 +201,33 @@ class OrchestratorEngine:
             task.task_id,
         )
 
+        # Emit plan to frontend as a visible block
+        plan_tool_id = f"plan_{task.task_id}"
+        plan_steps_list = [
+            {"step": i + 1, "agent": s.agent_role, "description": s.description}
+            for i, s in enumerate(plan_result)
+        ]
+        await self.sse.emit(
+            EventType.TOOL_STARTED,
+            {"tool": "plan", "step": 0, "tool_call_id": plan_tool_id},
+            session_id=session.session_id,
+        )
+        plan_text = "\n".join(
+            f"  {s['step']}. [{s['agent']}] {s['description']}"
+            for s in plan_steps_list
+        )
+        await self.sse.emit(
+            EventType.TOOL_COMPLETED,
+            {
+                "tool": "plan",
+                "status": "completed",
+                "summary": f"Plan: {len(plan_result)} steps",
+                "raw_output": f"Plan de ejecución ({len(plan_result)} pasos):\n{plan_text}",
+                "tool_call_id": plan_tool_id,
+            },
+            session_id=session.session_id,
+        )
+
         # 3. Execute each step — failures are logged and skipped
         results: list[dict[str, Any]] = []
         failed_steps: list[int] = []