Difficulty Scaling

Difficulty adjusts based on observable signal. Each epoch the parent substrate is re-evaluated to set a baseline. The minimum-improvement threshold adjusts based on the rate of state advances and quality attempts. Hidden-pack quotas keep the hardest strata represented as the corpus grows. Without quotas, the sampled pack would slowly drift toward whichever stratum had the most records, and the hardest categories (multi-hop relation, temporal current-versus-stale) would get under-tested.

Large corpus deltas freeze the threshold for one epoch. That is the only manual safety valve; everything else is reactive to live activity.