Reaching the tip needed two historical facts encoded, and the second one was
not in the original hypothesis.
First, the disarmed window: 36 anchor heights (13,267,824 to 13,268,944) whose
blocks carry an attached certificate but no digest, and whose signer indices are
not strictly increasing, produced while anchoring was disarmed fleet-wide to
unblock the chain after an incident. Encoded as a named list of historical
windows with fixed bounds in code, after the precedent of the base-fee lapse
windows: inside, the header is accepted as written; outside, nothing changes.
Second, the recovery, found by measuring rather than guessing. After the
emergency re-arm the fleet ran for a stretch with a lowered seal threshold, so
proposers legitimately wrote shorter certificates. Its extent was measured by
reading 25,252 anchor heights one at a time, with NO binary search, because the
property is not monotone: only about 15 percent of heights are affected and the
largest gap between two affected heights is 44, so a binary search would have
returned an answer that looks exactly like a good one. Result: 13,268,976 to
13,890,544, thresholds measured at 1 or 2, never 0.
The second window relaxes the seal COUNT only. Digest binding and index
ordering stay enforced and every seal is still verified. Widening the disarmed
window to cover both would have been easier and would have thrown away
certificate binding on 19,425 anchor heights, which is the one property the
anchor exists for.
Negative control in four directions, because an exception can fail both ways:
the window predicate forced always-false turns 10 tests red; forced always-true
turns 39 red, of which 22 are pre-existing strictness tests, making the
exception swallowing the chain visible; the historical threshold emptied turns 7
red; pinned at 1 turns 8 red. Restored: 641 tests, 0 failures, counted from XML.
Patch verified on a pristine upstream checkout, alone and in series, and the
resulting tree compiles.
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