Constant SPEND_MAP_RETENTION_BLOCKS 

pub const SPEND_MAP_RETENTION_BLOCKS: u32 = 100;

The number of trailing blocks in a batch whose spend-map entries are always retained, even when put_blocks_rows can prove that insertion is skippable. This keeps the maps’ contents aligned with a LowLevelWalletWrite::prune_tracked_spends pruning depth of the same value, and comfortably exceeds the maximum reorg depth the wallet tolerates.