Merge branch 'c-screw-undetermined' into pool-C

docs/RUGNUX_REPORT.md

@@ -199,6 +199,19 @@ partner among them — and, on a group that has such a partner, `SPACE_GROUP_ENA
 whether the hand is open (`UNDETERMINED`), asserted by the user (`GIVEN`), or taken from an accepted
 model (`ASSUMED_FROM_MODEL`).
 
+`SPACE_GROUP_SCREW_UNDETERMINED=` names the **axes whose screw these data could not decide at all**,
+as one or more of `a`, `b`, `c`; when every screw the data could show was judged it reads `NONE`
+and, like the other keys whose answer is "nothing to report", is written only with `--developer`. It
+fires when the axial row a screw lives on was never recorded — it lay in the spindle's blind cone,
+or outside the resolution range — so nothing was measured that could confirm or refuse the screw.
+On such an axis `SPACE_GROUP_NAME=` is not an answer: the answer is that group **or** any of
+`SPACE_GROUP_ALTERNATIVES`, and no measurement in the run chooses between them. What is written to
+the `.mtz`/`.cif`/`.hkl` is unchanged — the member claiming no screw, because a reflection file must
+carry one group — and the report prints the axis, why the row could not be judged, and what the
+alternatives are. To settle it, record the missing row: a different crystal orientation, or a sweep
+that reaches it. With `--developer` the space-group section names the same axes in prose beside the
+per-zone screw table.
+
 `SOHNCKE_SPACE_GROUP=` in section 2 is written on every run whose space group was determined by the
 search; a run given its group with `-S` has no Sohncke candidate to name and omits the key. Where the
 search found a glide plane, `SPACE_GROUP_NAME=` names the group with it and this names the best group