nmc(P1c): AuxPow::check_proof parent-coinbase tx-merkle leg (step 3) + witness-stripped txid KAT - #181
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frstrtr merged 1 commit intoJun 19, 2026
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…p 3) + witness-stripped txid KAT Adds nmc::coin::parent_coinbase_txid() (Hash over TX_NO_WITNESS serialization, byte-identical to btc compute_txid() but NMC-local per the coin fence) and wires AuxPow::check_proof step 3: reconstruct the parent block tx-merkle-root from the witness-stripped coinbase txid through parent_coinbase_branch/index via aux_merkle_root(). When a parent header is present the reconstructed root MUST equal parent_header.m_merkle_root, else INVALID; malformed legs (negative index, index wider than branch depth) are INVALID. Steps 2 (MM-marker commitment) and 4 (parent PoW) remain unbuilt, so a structurally-consistent proof still returns INCOMPLETE, never VALID -- NMC MUST NOT block-validate off this leaf. The load-bearing KAT asserts the exact byte serialization: the txid is hashed over the LEGACY (no-witness) layout -- txid, NOT wtxid -- re-derived field-by- field without SerializeTransaction's witness/marker path, and is shown to differ from the wtxid for a coinbase carrying the BIP141 reserved value. Plus 4 check_proof boundary KATs (match=>INCOMPLETE, mismatch/negative/too-wide=> INVALID). nmc_auxpow_merkle_test 14/14 PASS exit 0. NMC-local, btc tree READ-ONLY, test target name unchanged (CI allowlist untouched).
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Stacked PR — review order P1a (#178) -> P1b (#180) -> P1c (this). Base is the P1b branch so this diff is P1c-only; each leg is independently revertable.
What
Third leg of
AuxPow::check_proof(): the parent-coinbase tx-merkle proof (step 3 of 4).nmc::coin::parent_coinbase_txid()—Hash(pack(TX_NO_WITNESS(tx))), byte-identical to the btc tree'scompute_txid()(mempool.hpp) but NMC-local per the coin fence (onlynmc::coinserializer +core::Hash; no btc include).check_proofstep 3: reconstruct the parent block tx-merkle-root from the witness-stripped coinbase txid throughparent_coinbase_branch/parent_coinbase_indexviaaux_merkle_root(). When a parent header is present the reconstructed root MUST equalparent_header.m_merkle_root, else INVALID. Negative/too-wide index => INVALID.Still INCOMPLETE-never-VALID
Steps 2 (MM-marker commitment + chain_id/slot binding) and 4 (parent PoW vs target, btc tree READ-ONLY) are unbuilt. A structurally-consistent proof returns INCOMPLETE — NMC MUST NOT block-validate off this leaf. No leaf can block-validate until all four legs land, so this carries no merge risk.
Tests —
nmc_auxpow_merkle_test14/14 PASS exit 0 (was 9/9)SerializeTransaction's witness/marker path (catches a stray marker/flag), and shown to differ from the wtxid for a coinbase carrying the BIP141 reserved value.check_proofboundary KATs: match=>INCOMPLETE, mismatch/negative/too-wide=>INVALID.Fences
NMC-local (
src/impl/nmc/only), btc tree READ-ONLY, GPG-signed, zero-attribution, test target name unchanged (CI--targetallowlist untouched). I do not self-merge.Next: P1c-step2 (coinbase MM-marker scan + chain_id pin), then step 4 (parent PoW).