channels_sv2: document why coinbase scriptSig length prefix is always 1 byte - #2244
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scriptSig length prefix is always 1 bytechannels_sv2: document why coinbase scriptSig length prefix is always 1 byte
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The prefix/suffix split indexes in JobFactory hardcode a `1 // bytes in script` term for the scriptSig CompactSize length prefix. CompactSize switches to a 3-byte encoding at 253 bytes, so the hardcoded 1 looks like an off-by-2 hazard on inspection. It is not: Bitcoin consensus limits the coinbase scriptSig to 100 bytes, unconditionally below the 253-byte threshold. Any input that would push the scriptSig past 252 bytes is already consensus-invalid for reasons that have nothing to do with the split. Add a comment stating that rationale at each of the four sites so the assumption doesn't have to be re-derived. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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The prefix/suffix split indexes in
JobFactoryhardcode a1 // bytes in scriptterm for thescriptSigCompactSizelength prefix.CompactSizeswitches to a 3-byte encoding at 253 bytes, so the hardcoded 1 looks like an off-by-2 hazard on inspection.It is not: Bitcoin consensus limits the coinbase tx
scriptSigto 100 bytes, unconditionally below the 253-byte threshold.Any input that would push the scriptSig past 252 bytes is already consensus-invalid for reasons that have nothing to do with the split.
This PR adds a comment stating that rationale at each of the four sites so the assumption doesn't have to be re-derived.
close https://github.com/project-loupe/audit-stratum/issues/19