The measured-centre arm is a whole geometry pre-pass. It now integrates first a third of the pre-pass
frames, in 3k + 1 blocks of about 10 deg over the whole pre-pass arc with every third kept, and the
file's centre merges the same frames (its outcomes for the other frames are moved out while that
engine ingests). Where the measured centre loses on that subset on every line MeasuredCentreWins draws
by more than NEAR_TIE_SIGMA times the line's noise (Poisson for the strong counts, the Fisher standard
error for a CC1/2), it has lost and no full arm is run. Anything else, a near tie or a win, puts the
run back as the file's centre left it and runs the arm over all the pre-pass frames, deciding as before.
The run made again (decide_all_late_) runs the arm on all frames.
The same subset was tried for the metric-symmetry demoted arm and the walk refits and is not used
there: the held-out residual's standard error does not grow on a third of the frames, so a subset
margin overstates the evidence (one set's metric call flipped at 2.07 sigma), and a subset refit moved
one walk to a worse fixed point.
Against rc175 edde4439c, ci + 49 extra + 9 private sets: p.hkl and MTZ data identical on all 86. The
arm lost on the subset on 22 sets (no full arm), was a tie/win on 9 (full arm as before, +0.3-1.7 s).
Alternated runs: one set 62.1 -> 55.2 s, another 46.2 -> 42.4 s.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EizBKhTqrAYago9KJG3dA3
leonarski_fandClaude Opus 5.5
94a51ea1ae