fix(langfuse): v4 가 옛 ingestion 을 거부 — OTLP/HTTP JSON(/api/public/otel/v1/traces)으로 전환, 로컬 Langfuse 실측 통과. 사용자·세션 속성은 자식 span 에도 복사

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

5_django_backend/apps/chat/stream.py

@@ -256,13 +256,14 @@ async def _finalize(session: ChatSession, state: TurnState, started: float, *, f
         tid = f"{session.id}-{int(started * 1000)}"
         user_email = await sync_to_async(lambda: session.user.email)()
         meta = {"failed": failed} if failed else {}
+        t0 = datetime.fromtimestamp(started, timezone.utc).isoformat()
+        root = langfuse.trace(tid, "chat", userId=user_email, sessionId=session.id, input=state.user_text,
+                              output=content, metadata=meta, tags=["codeassist"], start=t0, end=langfuse.now_iso())
         langfuse.send_later([
-            langfuse.trace(tid, "chat", userId=user_email, sessionId=session.id, input=state.user_text,
-                           output=content, metadata=meta, tags=["codeassist"]),
+            root,
             langfuse.generation(
-                tid, "opencode-turn",
-                startTime=datetime.fromtimestamp(started, timezone.utc).isoformat(),
-                endTime=langfuse.now_iso(),
+                tid, "opencode-turn", parent=root,
+                startTime=t0, 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 "",