from __future__ import annotations
import re, json
CIT = re.compile(r"\[(E_[A-Z0-9._-]+)\]")
def citation_coverage(text:str)->float:
    # sentence-level coverage
    s=[x.strip() for x in re.split(r"(?<=[.!?])\s+", text.strip()) if x.strip()]
    if not s: return 0.0
    ok=sum(1 for x in s if CIT.search(x))
    return ok/len(s)
def is_json_only(text:str)->bool:
    t=text.strip()
    if not (t.startswith("{") and t.endswith("}")): return False
    try:
        json.loads(t); return True
    except Exception:
        return False