feat(dataset): admit four 2018 AntPool parent-reuse blocks

[deadmanoz]

Summary

Four AntPool blocks from 2018, at heights 507514, 509557, 515319 and 534339, include non-coinbase transactions that their canonical parent had already confirmed, so ConnectBlock fails at CheckTxInputs with bad-txns-inputs-missingorspent. 515319 is a complete copy of its parent's 79 non-coinbase transactions; the other three carry a subset or a mix of parent transactions and new ones. The same AntPool worker mined parent and child each time, which reads as a template that updated hashPrevBlock without rebuilding the transaction list: the sibling of 584802 (#11), where the transactions were dropped and their fees kept.

No existing rule looks at the parent's transaction list, so these passed every context-free body check. The new rule already_confirmed_in_parent keeps the same reject string and requires a complete body plus a parent_txid that is a non-coinbase transaction in both the body and the canonical parent (schema section). ci/prevouts.py fetches the parent header, which must hash to prev_hash, and the parent's ordered txid list, which must reproduce that header's merkle root, then checks membership with the parent's coinbase excluded. The canonical hash at height minus one must equal prev_hash. The evidence is cached as {prev_hash}.header, {prev_hash}.txids.json and height-{n}.hash. Only the immediate parent is considered. Core skips BIP30 below height 1983702 on the known chain (guard in validation.cpp), so the named failure is the reuse of spent inputs, not bad-txns-BIP30.

Each record carries pool: AntPool with pool_basis: tag, since every coinbase scriptSig contains Mined by AntPool (mining-pools), and one scrape observation citing the pinned chainquery snapshot in the mergedmonitor archive, whose tips file labels the four as invalid; that label started the search and is not the evidence. The bodies are byte-identical to the copies in stale-blocks abee96d. On 17 September 2026 a Bitcoin Core v31.1.0 node rewound to each parent returned bad-txns-inputs-missingorspent from submitblock for all four; the replay logs are held locally. Schema, notes and README are updated. The four rows and bodies come out of bitcoin-data/stale-blocks in a separate PR, following the stale-versus-invalid split in bitcoin-data/stale-blocks#128.

Testing

All 36 tests pass, including the new cases for a parent_txid absent from the body or from the parent list, the coinbase named as parent_txid, a list that does not match the merkle root, a non-canonical prev_hash, and a missing cached list. Offline python ci/sanity-check.py reports 52 blocks, 52 contexts, 195 observations and 10 block files; with --fetch-prevouts it downloads nothing and passes. The existing admissions are unchanged.