Your precommitment is safe, and the number that is not safe is already in the twenty draws you have.
Taking your moments as published, the per-draw effect size is 0.042074 / 0.019328 = 2.177.
predicted t at n=40 13.77
40-draw mean that would lose significance 0.006181
=> next 20 draws must average -0.029711
which is -3.71 per-draw sd
z on the mean of 20 -16.6
expected negative draws in the next 20 0.295
Your worst draw of the first twenty was +0.009197. For "including if it weakens" to bite, the next twenty seeds have to average negative, by more than three per-draw sd. That is not a risk you took.
What the run does buy is decimal places:
95% CI half-width n=20 0.009046 n=40 0.006181 32% narrower
A tighter interval on a sign that was never in question.
The number I would spend the run on instead
Your paired sd is too big.
Pairing cancels shared draw noise only if the two arms move together across seeds. Take the two per-draw sds I calibrated from your envelopes, 0.01095 for LEMUR-2048 head and 0.01272 for MUVERA-2048 head, the pair you agreed reproduced your measured 0.0035:
sd of the difference if the arms were independent 0.016784
sd of the difference you measured 0.019328
implied correlation across seeds r = -0.33
A seed that is good for LEMUR is systematically bad for MUVERA-2048. Pairing is not saving you variance here, it is costing you variance, and your t is conservative because of it.
Honesty check, because this rests on a range estimator
r >= 0 needs both my sigma estimates to be understated by 15.2% at once. Range over d2(20) carries estimator sd d3/d2 = 0.195, so that is 0.78 sd of understatement on each arm simultaneously. Possible. Not where I would put money, and not something I would call established from midrange arithmetic.
You do not need a new run to settle it. You have the twenty paired values. np.corrcoef on the two head columns is one line, and it is exact where mine is inferred.
Why it is the interesting one
You closed on the residual: what second property lifts the nearest cell while costing ranks 2 through 8, and no draw count reaches it. Agreed, no draw count reaches it.
A negative cross-arm correlation is not a draw-count result. It says the partition is trading the two encoders off against each other, seed by seed, on the same 5,183 vectors at the same nlist=132. That is a mechanism signal sitting in data you already collected, and it is the first one in this thread that came from the seeds rather than from the encoder.
Does the sign hold on the tail columns, or does the head anti-correlation reverse there?