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The spec bounds an uncle's own slot (0 < sl_A - sl_U <= w_u) but leaves its PARENT unconstrained beyond lying on the referencing chain. So a block minted NOW, built on a chain block from arbitrarily far back, is a legal first-fork uncle: recent by its own slot, ancient by its parent's. Verifying it means deriving the epoch state and ledger root as of that ancient parent, per reference, and those are precisely the inputs the counting rules require -- so the work cannot be amortised. It costs the adversary nothing beyond lottery wins it already has; it just builds them somewhere useless. Measured with a deep_parent coalition. At the deployed operating point a 30% adversary moves the MEDIAN counted reference's reach from 54 slots back to 20,144, and the worst case to 76,778 -- the epoch boundary, ~21 hours of history, ~256x the nominal window. It is not a tail effect. The fix is a SUBSTITUTION, not an additional rule. A block strictly postdates its parent and a referenced uncle strictly precedes its referencer, so sl_A - sl_U < sl_A - sl_parent(U) <= w_u: bounding the parent bounds the uncle for free, and a both-windows variant would be identical to the parent one. Both invariants are pinned in a new test_slot_ordering.py rather than argued -- the user asked to confirm sl_A > sl_U explicitly, and it turns out to be load-bearing for the whole implication, so it is tested at three geometries plus a hand-built counting case. Under the parent anchor the same coalition reaches 292/300/300 slots at delta_max 4/8/16 -- capped by construction. Honest recovery is unaffected: 0.9993 -> 0.9999, 0.9969 -> 0.9986, 0.9791 -> 0.9858, no loss anywhere within one to two SEM, because a latency orphan's parent is recent by construction. One finding that sharpens the case: at delta_max = 16 the HONEST uncle-anchored arm already reaches 315 slots, past its own w_u = 300. Under the current rule w_u is not a bound on validation reach even with no adversary present. It only becomes a state-retention bound once anchored to the parent. Recorded as sec 6.12 with fig38, a new row in the sec 8.5 spec deltas, both new knobs in sec 7, and the study in sec 9. uncle_window_anchor and the deep_parent strategy are appended to the RNG key only when non-default, so no committed run is reseeded. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>