fix: use UTXO state root in block producer

[createkr]

Summary

BlockProducer.get_state_root() currently commits the legacy account-model balances root even when the node is operating against the UTXO database. This patch lets BlockProducer prefer utxo_db.compute_state_root() whenever a UTXO handle is available, while preserving the legacy balances-table path as a fallback.

What changed

• add an optional utxo_db handle to BlockProducer
• prefer the UTXO Merkle root in get_state_root() when utxo_db is attached
• fall back to the legacy balances-table root when no UTXO DB is present or UTXO root computation fails
• add focused state-root regression coverage

Validation

• PYTHONPATH=node python3 -m py_compile node/rustchain_block_producer.py node/test_block_producer_state_root.py node/utxo_db.py
• PYTHONPATH=node python3 node/test_block_producer_state_root.py

Reviewer note

The semantic change is intentionally small (constructor wiring + get_state_root() preference/fallback logic + focused tests). If GitHub shows the Python file as a large diff, that is due to repository line-ending normalization noise around this file history rather than broad logic churn.

[zhuzhushiwojia]

Good catch! This fix addresses an important issue. The approach looks correct.

[zhuzhushiwojia]

Great fix! The change to use state_root from the UTXO model in the block producer is a solid improvement. A few observations:

Code Quality:

• Changes look clean and well-structured
• New test file covers state root verification

Suggestions:

• Consider adding edge case tests for genesis block (height=0)
• Could add integration test with real UTXO set operations

Overall LGTM! ✅

[Scottcjn]

Reviewed. Block producer now uses UTXO Merkle state root when utxo_db is available, with clean fallback to legacy account-model balances. Soft import of utxo_db avoids hard dependency. 7 tests cover: UTXO preferred, fallback on failure, determinism, spend-changes-root, empty set. Good work.

Payment: 50 RTC (Medium-High — consensus state root integrity)

Thank you @createkr.