Function needs_prev_shard_check 

pub fn needs_prev_shard_check(
    rank: u64,
    found_block: Option<u64>,
    block_number: BlockNumber,
) -> bool

Checks if a previous shard lookup is needed to determine if we’re before the first write.

Returns true when rank == 0 (first entry in shard) and the found block doesn’t match the target block number. In this case, we need to check if there’s a previous shard.