BIP54 proposes contraining the cointbase transaction nLockTime and nSequence fields. Our internal mining code has been doing this since #32155, but currently the fields are only communicated to IPC clients (see e.g. #33819).
This PR extends the getblocktemplate RPC to provide these fields.
Accompanying proposed extension to BIP54: https://github.com/bitcoin/bips/pull/2097
Even if BIP54 never activates, it makes sense to serve these new fields.
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For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/34419.
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| Concept ACK | jonatack |
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Added the coinbase nVersion.
Expand the getblocktemplate RPC result with two fields to prepare
for a possible BIP54 deployment in the future.
I dropped nVersion from the proposal, see https://github.com/bitcoin/bips/pull/2097#issuecomment-3997488850.
Although it's harmless to add, I also dropped it from the implementation here for clarity. It can be added in a followup.
Concept ACK