§63 has defined T0/T1/T2 since Phase 26 and never enforced it. Two measured consequences in
SESSION-20: ~13 full clean-fleet verifies (~15 min each) for batches that were provably T1
(over-verification), AND two cases where the write set was LARGER than the belief about it — the §85
widen believed contained to one overlay broke ov_SC01_077, and gate_stage's ARITY pre-pass silently
rewrote 40 TUs (under-verification, the dangerous half).
A tier is a CLAIM about the write set; this turns it into a MEASUREMENT. --expect t1 fails loud when
the tree disagrees. Binary list DERIVED from config/splat.*.yaml (R33, never hardcoded — R36's
incident was a hardcoded set missing 4 real binaries). Coverage ASSERTED (R32): an unclassified path
exits 2 and names itself rather than being silently skipped. overlays.mk is attributed per-binary by
parsing its diff, so a change confined to one binary's var-block stays T1.
Drew T