[ZocoLini]

Closes #1129. Part of #1047.

CbTx version 4 (dashpay/dash#7639) adds merkleRootAssetUnlocks after creditPoolBalance, and every coinbase must be v4 once v24 activates. We stopped reading after asset_locked_amount, so a v4 coinbase left 32 bytes unread and misaligned the rest of the block, and re-encoding dropped the field (wrong txid and block merkle root).

Changes

• New MerkleRootAssetUnlocks hash type.
• CoinbasePayload::merkle_root_asset_unlocks: Option<MerkleRootAssetUnlocks>, read and written from version 4 and counted in size(). Encoding a v4 payload without it errors, like the v3 fields.
• CURRENT_VERSION stays 3: Core rejects v4 until v24 activates.
• Hand-written bincode impl with the derived layout, writing the new field only from version 4. The derive would add a trailing Option tag to every payload and break decoding of data persisted before (the dash-spv QRInfo fixtures failed with it).

Breaking: new public field on CoinbasePayload.

Modelling note

I'd prefer the field to be mandatory, as in Core: a plain uint256 in CCbTx that stays null unless version >= 4, where it is always serialized (all zeros when the block has no v2 unlocks). That would rule out a v4 payload without the root. It is an Option here to follow the existing pattern of the v3 fields (best_cl_height, best_cl_signature, asset_locked_amount). Changing that is better done for all of them in a separate PR.

Testing

• Unit: size for v1-v4, v4 consensus round trip (root at the end, exact bytes consumed), v4 bincode round trip, v4 without the root fails to encode.
• cargo test -p dashcore -p key-wallet -p key-wallet-ffi, cargo test -p dash-spv with dashd integration tests, clippy -D warnings.
• No real v4 coinbase vector yet: our regtest dashd doesn't run v24.

🤖 Generated with Claude Code

PR Hygiene · 095cfc6

• Bots — coderabbitai skipped after its own rate limit
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  • files with no dedicated owner (dash/src/blockdata/transaction/special_transaction/coinbase.rs, dash/src/hash_types.rs, key-wallet-ffi/src/special_payload.rs) — QuantumExplorer or xdustinface
  • key-wallet (key-wallet/src/transaction_checking/transaction_router/tests/classification.rs, key-wallet/src/transaction_checking/transaction_router/tests/coinbase.rs, key-wallet/src/wallet/managed_wallet_info/transaction_builder.rs) — QuantumExplorer or xdustinface

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📥 Commits

Reviewing files that changed from the base of the PR and between 67b307c and 095cfc6.

📒 Files selected for processing (6)

• dash/src/blockdata/transaction/special_transaction/coinbase.rs
• dash/src/hash_types.rs
• key-wallet-ffi/src/special_payload.rs
• key-wallet/src/transaction_checking/transaction_router/tests/classification.rs
• key-wallet/src/transaction_checking/transaction_router/tests/coinbase.rs
• key-wallet/src/wallet/managed_wallet_info/transaction_builder.rs

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[codecov]

Codecov Report

❌ Patch coverage is 97.08738% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.93%. Comparing base (67b307c) to head (095cfc6).

Files with missing lines	Patch %	Lines
...ckdata/transaction/special_transaction/coinbase.rs	97.02%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1137      +/-   ##
==========================================
+ Coverage   77.92%   77.93%   +0.01%     
==========================================
  Files         302      302              
  Lines       79108    79209     +101     
==========================================
+ Hits        61644    61733      +89     
- Misses      17464    17476      +12     

Flag	Coverage Δ
core	75.10% <97.02%> (+0.13%)	⬆️
ffi	51.14% <100.00%> (-0.01%)	⬇️
rpc	48.95% <ø> (ø)
spv	92.34% <ø> (-0.06%)	⬇️
wallet	81.99% <100.00%> (+<0.01%)	⬆️

Files with missing lines	Coverage Δ
dash/src/hash_types.rs	55.43% <ø> (ø)
key-wallet-ffi/src/special_payload.rs	92.25% <100.00%> (+0.02%)	⬆️
.../wallet/managed_wallet_info/transaction_builder.rs	92.73% <100.00%> (+<0.01%)	⬆️
...ckdata/transaction/special_transaction/coinbase.rs	89.88% <97.02%> (+4.76%)	⬆️

... and 7 files with indirect coverage changes

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