feat(observability): Langfuse 전송 — 턴 마무리(사용자 trace)·게이트웨이(FabriX generation) 두 훅, SDK 없이 HTTP. deploy/langfuse 에 compose+env+반입 절차

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

5_django_backend/apps/chat/stream.py

@@ -20,12 +20,14 @@ import asyncio
 import json
 import logging
 import time
+from datetime import datetime, timezone
 
 from django.conf import settings
 from django.http import StreamingHttpResponse
 from django.views.decorators.csrf import csrf_exempt
 
 from apps.accounts.authentication import user_from_token
+from apps.gateway import langfuse
 from asgiref.sync import sync_to_async
 from common.envelope import json_error
 from common.opencode_service import opencode_service
@@ -248,6 +250,25 @@ async def _finalize(session: ChatSession, state: TurnState, started: float, *, f
     if title:
         session.title_llm = title[:200]
     await session.asave(update_fields=["is_generating", "title_llm", "updated_at"])
+
+    # 관측: 사용자 단위 trace 하나 + 답변 generation 하나. 실패해도 여기까진 이미 저장됨.
+    if langfuse.enabled():
+        tid = f"{session.id}-{int(started * 1000)}"
+        user_email = await sync_to_async(lambda: session.user.email)()
+        meta = {"failed": failed} if failed else {}
+        langfuse.send_later([
+            langfuse.trace(tid, "chat", userId=user_email, sessionId=session.id, input=state.user_text,
+                           output=content, metadata=meta, tags=["codeassist"]),
+            langfuse.generation(
+                tid, "opencode-turn",
+                startTime=datetime.fromtimestamp(started, timezone.utc).isoformat(),
+                endTime=langfuse.now_iso(),
+                input=state.user_text, output=content,
+                usage=langfuse.usage_of(usage["input"], usage["output"]) if usage else None,
+                level="ERROR" if failed else "DEFAULT", statusMessage=failed or "",
+                metadata={"elapsed_ms": usage["elapsed_ms"]} if usage else {},
+            ),
+        ])
     return usage, title