RESULT-CHANGING.
AnalyzeTwinImmuneZones flags zones_ambiguous when the acentric control reads more compressed
than a perfect twin's 0.541 by three standard errors: no twin fraction can do that, so something
else (overlapping spots, neighbour correlation) averages reflections with unrelated ones, it
compresses the zones too, and a genuine centric zone then reads acentric. SearchSpaceGroup's own
zone gate already skips such a reading, and the struct documents that no verdict is read from it
either way - but Rugnux's TwinZoneVerdict still returned -1 on it, only noting the ambiguity in
its text, and so let a refusal stand on a zone it had just called uninformative.
9zmu (deposited P6522, c ~493 A, 95% of predicted spots overlap a neighbour) regressed in rc176
from P6122 (enantiomorph, pass) to P321: its P1 <|L|> of 0.394 (overlap, not twinning - second
moment 2.23; the model's twin fraction 0.08 and R-free 0.287 twinned or not) put it in the
partial-twin band, so since 7c1befd48 the search asks the zone of the holohedral 622 too. On the
Lorentz-filtered merge the control read 0.552 +- 0.002 (just inside the twin range) and the zone
-1378 nats, so that arm refused 622; the all-observation arm confirmed it, and the arbitration
read the zone on the all-observation merge: control 0.513 (ambiguous), zone -319 nats, verdict
-1, refusal stands, P321. Now that reading is undecided, the rule stays as before the zone was
asked, and the all-observation 622 is taken: P6122 again, R-free 0.2825 (as rc175).
Changed: 9zmu P321 -> P6122 (pass). Unchanged against rc176 run 20261017-1924 (space group,
verdict, ISa, R-free identical): 3r6o I41, 8c3e P321, 3mc4 R3, and every other open set whose
rc176 log has REFUSED / twin-immune / "Twinning indicators BEFORE" (2wnn 4bwl 5ebi 5j23 6fid
6iu6 6iu8 6iu9 6p8j 6pxb 6pxc 6vww 6z9g 6zqr 7k1l 7kcn 8xte 8xtg 9fcf 9hnc 9hs7 9i80 cuhf2),
20 random passing open sets (2wnz 3p85 5jvn 6cdl 6f3p 6u7g 6zr0 7n2s 7orr 7os3 7ou1 7tcd 8egn
8xbp 8y74 9min 9rp9 9t6s 9v16 9yzk) and the five in-house sets with a TWIN_ZONE_DECISION.
In rc176 9zmu was the only set whose decisive zone verdict was an ambiguous one.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PXc1zD1yxHqaR1DGdCTHL4
leonarski_fandClaude Opus 5.5
ced0ac4bdd
