The fair search's depth gradient continues past the fourth ply once the chance estimator is exact

The fifth ply buys nothing at either chance resolution, and the earlier interim reading that it was actively harmful is withdrawn. Complete leg, 64 of 64 games: depth 5 at five strata scores 288,704 against depth 4 at five strata's 297,327, a paired -8,624 with a one-sided 95% whole-game bootstrap lower bound of -55,134 and W-T-L 33-0-31, for 23.29x the logical work per move. That is a wash, not a reversal. Partial leg, 16 of 64 games and still running: depth 5 at seven strata is -1,581 against the depth-4 seven-stratum control (95% lower bound -173,154, W-T-L 7-0-9) at 34.32x the work, and +16,622 against depth 3 at seven strata (95% lower bound -130,027, W-T-L 8-0-8) at 1,084.78x the work. At a fixed stratum count, depth 3 -> 4 -> 5 does not separate. READ THIS BEFORE QUOTING THE MEANS: the eye-catching gap between the 398,498 of d4s7 and the 288,704 of d5s5 is a chance-samples effect and not a depth effect, because those two arms differ in both factors; the correct paired depth contrasts at fixed chance resolution are d5s5 - d4s5 = -8,624 and d5s7 - d4s7 = -1,581, both indistinguishable from zero, and the correct paired stratum contrast at fixed depth is finding-05's d4s7 - d4s5 = +101,171. The interim slice reported in finding-15 section 2.2 (-268,611 over 8 paired games) was completion-order biased against depth 5 exactly as that section warned; at 16 games the bias is gone and the delta is -1,581. The engine control is clean and is the other retained result here: the fast engine's depth-4 seven-stratum arm reproduces the recorded unoptimised arm over 64 paired games x 11 fields with 0 mismatches, and the depth-5 five-stratum arm reproduces the recorded 32-game unoptimised arm over 32 paired games x 11 fields with 0 mismatches across two binaries and two different cache capacities. Every arm audited 0 incomplete decisions at its requested depth, 0 censored games and 0 score-decomposition identity failures. Flow rates fall with depth at five strata (1.9387 clears and 1.0651 reveals per move against depth 4's 1.9489 and 1.0697, and against the 2.400 and 1.400 indefinite survival needs), so nothing here moves toward the target.

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.