Every model that played the D5 set complained about the same moment: two
pieces left, interlocked, and nothing on the board saying which way to turn.
codex-spark took it to the end — it cycled all six orientations on L18 and
gave up on a level that was solvable, with clarity rated 5. Replaying the
position shows exactly one of the six orientations releases anything.
deadTurnAudit now reports endgameMinOpen: across reachable states with three
pieces or fewer left, the fewest orientations that release anything. It is
computed inside the walk that was already happening, so it costs nothing. The
generator requires at least two.
The gate picks out precisely the four levels every model stalled on, with no
false positives — the other fourteen already had two or three. Regenerating
drops the spiral family entirely: its structure produces single-exit endgames
by construction, not by unlucky seed.
Measured on the regenerated set, rule bot first and then grok-4.6 xhigh over
all 18:
blind rotations 1.17 -> 0.29 per level
extra rotations 1.22 -> 0.35
dead taps 2 -> 0
run time 55.5s -> 34.7s
stuck rating 1.89 -> 1.41 (this metric repeats at r = 0.85)
"which way do I turn" complaints 22% -> 12% of levels
The gate is a floor, not a difficulty dial: difficulty also fell, 2.39 -> 2.12,
because the levels it removes are the hard ones. And it treats a symptom — the
t0/t3 interlock is what the four-piece chain in createDeepLock builds by
construction, so the complaint is halved rather than gone.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
