Look up block by height, LT, or timestamp

curl --request GET \
  --url https://toncenter.com/api/v2/lookupBlock

{
  "ok": true,
  "result": {
    "@type": "ton.blockIdExt",
    "workchain": -1,
    "shard": "-9223372036854775808",
    "seqno": 51148869,
    "root_hash": "HxogBiV2YA+KrC9cJa5llfvDGNk2hwCqsaCSYo40V00=",
    "file_hash": "h7LOaX0cTqc8qKecsNYi32SVu0McCito3P2qzynvdqk=",
    "@extra": "1755814026.5747118:7:0.2443600480097572"
  }
}