move Langfuse to shared lng cluster, add trace instrumentation

api/main.py

@@ -23,19 +23,25 @@ logging.basicConfig(
 )
 
 
+_langfuse_client = None
+
 def _get_langfuse():
-    """Lazy Langfuse client — returns None if not configured."""
+    """Singleton Langfuse client — returns None if not configured."""
+    global _langfuse_client
+    if _langfuse_client is not None:
+        return _langfuse_client
     try:
         from api.config import get_settings
         s = get_settings()
         if not s.langfuse_public_key or not s.langfuse_secret_key:
             return None
         from langfuse import Langfuse
-        return Langfuse(
+        _langfuse_client = Langfuse(
             public_key=s.langfuse_public_key,
             secret_key=s.langfuse_secret_key,
             host=s.langfuse_host,
         )
+        return _langfuse_client
     except Exception:
         return None
 
@@ -175,7 +181,7 @@ async def trigger_fce(req: FCERequest):
             logger.error("agent_error agent=fce run_id=%s error=%s", run_id, e)
         finally:
             if lf:
-                lf.shutdown()
+                lf.flush()
 
     logger.info("agent_start agent=fce run_id=%s flight=%s", run_id, req.flight_id)
     asyncio.create_task(_run())
@@ -223,7 +229,7 @@ async def trigger_handover(req: HandoverRequest):
             logger.error("agent_error agent=handover run_id=%s error=%s", run_id, e)
         finally:
             if lf:
-                lf.shutdown()
+                lf.flush()
 
     logger.info("agent_start agent=handover run_id=%s hubs=%s", run_id, req.hubs)
     asyncio.create_task(_run())