A skyline may retain enough total empty area while no longer containing a box for its largest remaining square. Scan for the required consecutive low columns and reject such monotonic dead states.
Keep each pruning combination independently measurable and record the small public-path gain, the direct-order-9 regression, and the rejected periodic schedule.
Tests: Debug CTest (13 passed)
Tests: ASan+UBSan CTest (13 passed)
Refs: #15
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