ResultDepth x chance-exactness factorial: the fifth ply at five and at seven strata, with an end-to-end reproduction control

SUPERSEDES RS-20260821T181917Z-9a34ba02, which assessed this experiment when the depth-5 seven-stratum arm held 16 games. The arm was stopped by the repository owner's decision at the 32-game chunk boundary and will not be resumed, so its analysis is now FINAL even though the cohort is partial: 32 of 64 planned games, every one of them a whole game, 0 censored, 0 score-decomposition identity failures, 0 incomplete decisions, minimum completed depth 5. The old record remains committed history and is not edited. THE HEADLINE IS A CORRECTION, NOT AN UPDATE. The previous record read the fifth ply as 'does not separate'. That reading was a NON-MEASUREMENT REPORTED AS A NULL. Doubling the sample from 16 to 32 games moved the depth-5-minus-depth-4 seven-stratum contrast from -1,581 to +23,367 and its median from -39,660 to +18,820 - THE SIGN FLIPPED - which is what a quantity being estimated far below its detection floor looks like. By chunk the paired mean is -1,581 on the first 16 seeds and +48,315 on the second 16. Do NOT replace the old reading with 'depth 5 helps': +23,367 is equally unsupported. The one-sided 95% bootstrap lower bound is -83,046 and the contrast's detection floor at n=32 is 107,988, so the estimate sits at 22% of the smallest effect this cohort could have resolved. The correct statement is that THE FOURTH-TO-FIFTH PLY CONTRAST AT SEVEN STRATA WAS NEVER MEASURED, in either record. THE POWER ANALYSIS IS THE MOST USEFUL THING THIS EXPERIMENT PRODUCED. Detection floor, taken as 1.645 x sd / sqrt(n), the smallest true effect whose one-sided 95% bound would clear zero: d4s7-d4s5 +101,171 against a floor of 55,192 (n=64); d4s7-d3s7 +86,172 against 61,457 (n=64); d5s5-d4s5 -8,624 against 47,052 (n=64); d5s7-d4s7 +23,367 against 107,988 (n=32). EVERY SIGNIFICANT RESULT IN THIS FACTORIAL IS ABOVE ITS FLOOR AND EVERY NULL IS BELOW IT - the factorial separated the contrasts it had the power to separate and nothing else. Resolving the observed +23,367 needs about 684 paired games; finishing to the planned 64 would have left a standard error near 46,400 against a 23,367 estimate, still a non-measurement. That is the justification for the stop: the contrast is not answerable at any affordable cohort size, so the marginal machine-day buys no information. The variance is structural, not fixable by tidier running: the five largest single-seed paired deltas are -1,002,862, +958,985, -678,455, +592,546 and -577,069, so individual games swing by more than twice the cohort mean. WHAT IS ACTUALLY MEASURED HERE, and it is the same lesson from the other side: at depth 5, going from five to seven strata is worth +123,613 with a lower bound of +32,575, W-T-L 19-0-13 - SIGNIFICANT, and comfortably above its 95,207 floor - for 5.85x the work. The chance-exactness axis pays at depth 5 exactly as it pays at depth 4 (+101,171 [+47,447] there). The previous record's warning therefore survives and is strengthened: the eye-catching gap between d4s7's 398,498 and d5s5's 288,704 is a CHANCE-SAMPLES effect, not a depth effect, and both stratum contrasts are now significant while no depth contrast is. The engine controls are unchanged and clean: the fast engine's depth-4 arm reproduces the recorded unoptimised arm over 704 field comparisons with 0 mismatches, and the depth-5 five-stratum arm reproduces its recorded 32-game predecessor over 352 comparisons with 0 mismatches across two binaries and two cache capacities.