Why is difficulty adjustment tricky when Kaspa upgrades to 10 blocks per second?

Upgrading Kaspa's block rate to 10 bps creates a difficulty adjustment problem because the measurement window straddles two different eras. The difficulty adjustment algorithm (DAA) looks back over a window of recent blocks to decide how hard the next block should be to mine. When a speed upgrade happens mid-window, the early part of that window reflects the old, slower 1 bps rate while the later part reflects the new 10 bps rate — and without special handling, the algorithm would see "slow" blocks at the start and incorrectly slash the difficulty far too low. KIP-4 adds another wrinkle by switching from a full DAA window to a sparse one, so the transition logic must account for both changes at once. For miners and users, this matters because a badly miscalculated difficulty could temporarily let blocks be produced far too easily, disrupting the security and timing guarantees that Kaspa's consensus relies on.