out of curiosity can you post a diff between spreadx11 and standard x11
1. Each block is signed with the same key which is used in coinbase transaction and this signing must be performed in mining loop.
2. It is necessary to recompute whole block hash during mining.
These two things proof miner's knowledge of the whole block and ability to spend coinbase transaction. This prevents trustless pools because upon finding a block miner can broadcast it directly to the network and spend its reward.