from __future__ import annotations
import datetime as _dt, uuid

def utcnow() -> str:
    return _dt.datetime.now(_dt.timezone.utc).strftime("%Y-%m-%dT%H:%M:%S.%fZ")

def new_session_id() -> str:
    return str(uuid.uuid4())

def new_run_id(task_id: str, arm: str, rep: int, model_tag: str = "") -> str:
    base = f"{task_id}_{arm}_r{rep}"
    return f"{base}_{model_tag}" if model_tag else base