Admit 1Hash block 474294 under a new missing-parent-transaction rule

[deadmanoz]

Summary

Adds a missing_unconfirmed_parent evidence rule and the first block it admits: height 474294, 00000000000000000182acdf5657c93a0769dc6f9004047496b2e15efc6a4232, mined by 1Hash in July 2017.

Transaction 110 of the block spends b11a78c6c61af1cb37586f639050d74b95c2b0fd525623b6cb6a4bb4fba46a0e:1. That parent transaction is not in the block and did not exist at the tip of 474293, so ConnectBlock fails with bad-txns-inputs-missingorspent. Both transactions confirmed in the same-height competitor 000000000000000000db2504327e272fe7658fac0dd0741f46b212256e500886.

The existing bad-txns-inputs-missingorspent checker (477115, 809478) only recognises a parent that appears later in the same block. 474294 has none, and a prevout absent from the body is what every valid block looks like, so absence alone cannot be the evidence. The record therefore names the failing outpoint in a new missing_prevout context field, and CI checks that one outpoint rather than searching the block's 2,141 outside parents for one that happens to fit.

CI admits the record only if the body spends the recorded outpoint from a transaction that is not in the block; a public Esplora API reports prev_hash as the block at height 474293, so the candidate extends the canonical chain; the parent transaction is fetched, verified by txid and contains the spent output; and the API currently reports that transaction confirmed in another block at this height or later. That is, the parent was not in the chain below the candidate, so its output did not exist when the block was mined. An unconfirmed or unknown parent is not evidence, and a parent confirmed below this height is a normal spend.

CI does not rebuild the UTXO set at 474293 or replay ConnectBlock. It trusts the configured providers for the confirmation and the canonical hash (mempool.space and blockstream.info agree on the parent's confirmation), and the cached replies are snapshots from their first fetch. parent_kind remains a descriptive field on every record; the schema now says so.

Changes

• ci/prevouts.py: one fetch helper that returns bytes and one cached-lookup helper that decodes a file or downloads, decodes and then stores the reply. The same two functions now serve previous transactions ({txid}.bin), the /tx/{txid}/status reply ({txid}.status.json) and the /block-height/{n} reply (height-{n}.hash). That refactor is the first commit and changes nothing for the sigops path.
• ci/block_evidence.py and ci/sanity-check.py: omitted_prevouts, the confirmed_at_or_after inference, the RULES entry requiring missing_prevout, and the missing_parent evidence mode.
• data/invalid-blocks.jsonl and blocks/474294-….bin, byte-identical to the copy in bitcoin-data/stale-blocks at 2633e0e. Observations: the merge-mining-research Namecoin witness at child height 349887 and the chainquery.com orphan listing in NStifter/mergedmonitor. merge-mining-research still classifies the block as a stale; that reclassification is a separate change, after which the observation link will be repinned.
• docs/schema.md and docs/notes.md: the missing_prevout field, the evidence contract row, a section on why a later confirmation elsewhere proves the failure, and a plainer explanation of why ConnectBlock never runs when one of these blocks is replayed today.
• Tests cover the confirmation height boundaries, the admission failures for a malformed or unspent outpoint, a non-canonical previous block and a missing cache, and that unconfirmed or malformed replies are never cached.

Testing

python ci/sanity-check.py --fetch-prevouts admits 47 blocks with 6 block files and prints the fetched evidence for 474294: parent confirmed at 474294 in …500886, canonical block at 474293 equal to the record's prev_hash. The offline run passes with the three cached files present and fails naming the missing entry when the cache is incomplete. python -m unittest discover -s ci -p 'test_*.py' runs 32 tests. CI on this head: run 34950924462.

Related

bitcoin-data/stale-blocks#139 removes the invalid block from stale-blocks once this is published.

Original discussion: https://bitcointalk.org/index.php?topic=2041607.0.

[deadmanoz]

Drafting because I need to update the observation source in merge-mining-research so that the JSON entry has the correct "final" link (it needs to be demoted in that dataset to an error block)