Function synthetic_log_transaction 

pub fn synthetic_log_transaction(block_number: U256, chain_id: U256) -> Vec<u8> 

Build the deterministic payload of the synthetic transaction that carries a block’s “outside-of-frame” logs: logs emitted with no enclosing ethereum transaction (e.g. pallet-assets balance-change mirrors on non-eth_transact paths).

Shared by the runtime — which emits this transaction into the block so its logs enter the logs_bloom, receipts_root and transaction trie — and by the eth-rpc layer, which rebuilds the identical bytes to recover its hash. It is an unsigned legacy transaction distinguished only by nonce = block_number (so the hash is unique per block) and is not an executable transaction.