calibration: --no-refine-tilt holds the header tilt, it does not zero it

GuessInitialGeometry resets rot1/rot2/rot3 to zero before seeding, and the branch
that puts the header's tilt back was guarded by `refine_tilt && !tilt_refined`. With
--no-refine-tilt the tilt is never free, so tilt_refined is false, so the guard is
false, so the restore never ran - and the fit reported a zero tilt while the CLI
printed "held at the header value".

The guard only needs !tilt_refined: a tilt that was declined and a tilt nobody asked
to refine both want the header put back and the beam centre and distance refitted
around it. That is what the branch already does.

Measured on a LaB6 sweep with a tilt imposed on the command line and asked to be
held, --calibration spots:

  before  Rot1= +0.0000 deg  (+0.001400 rad from the header)
  after   Rot1= -0.0802 deg  (+0.000000 rad from the header)

The rings path reaches this only when the spot-derived start wins, which is why it
does not show on a file whose profile start is chosen; the spots path always did.
A calibration whose header tilt is already zero is unaffected - checked, byte-equal
distance either way.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EFEJG6WBQv8th4UJFNe53N

docs/CHANGELOG.md

@@ -17,6 +17,7 @@
 * Twinning is no longer reported when the L-test contradicts it.
 * The `rugnux` report gives the detector tilt and the direct beam beside the beam centre, and carries the tilt in the `dataset_settings` block.
 * The `rugnux` report gives the detector tilt rotation indexing measured, so it can be checked against a powder calibration.
+* `--no-refine-tilt` holds the detector tilt at the value in the file, instead of zeroing it, when the calibration starts from the spots.
 * The `jfjoch_viewer` grid scan view draws the cells in the proportion of the scan steps, so the map has the shape of the scanned area.
 
 ### 1.0.0-rc.165

image_analysis/geom_refinement/PowderCalibration.cpp

@@ -295,7 +295,12 @@ CalibrationResult CalibrateFromProfile(const std::vector<float> &profile,
             && (best->uncertainty.sigma_rot1_rad > 0.0 || best->uncertainty.sigma_rot2_rad > 0.0);
     const float significance = tilt_was_free ? TiltSignificance(best->geometry, best->uncertainty) : 0.0f;
     bool tilt_refined = refine_tilt && tilt_was_free && significance >= TILT_MIN_SIGNIFICANCE;
-    if (refine_tilt && !tilt_refined) {
+    // Not `refine_tilt && !tilt_refined`: with --no-refine-tilt the tilt is never free, so
+    // tilt_refined is false and this branch was skipped entirely - leaving the rotations at the ZERO
+    // that GuessInitialGeometry sets, while the CLI reported them as held at the header value. A
+    // declined tilt and a tilt nobody asked to refine both need the header put back and the rest
+    // refitted around it.
+    if (!tilt_refined) {
         // From the header's tilt, not from the one being declined. fit_from now takes a whole geometry,
         // so without this the "pinned" refit would pin rot1/rot2 at exactly the unvalidated values the
         // gate just rejected - which is the same fault the gate exists to catch, reintroduced one level
@@ -346,7 +351,12 @@ CalibrationResult CalibrateFromSpots(const std::vector<SpotToSave> &spots,
             && (unc.sigma_rot1_rad > 0.0 || unc.sigma_rot2_rad > 0.0);
     const float significance = tilt_was_free ? TiltSignificance(fitted, unc) : 0.0f;
     const bool tilt_refined = refine_tilt && tilt_was_free && significance >= TILT_MIN_SIGNIFICANCE;
-    if (refine_tilt && !tilt_refined) {
+    // Not `refine_tilt && !tilt_refined`: with --no-refine-tilt the tilt is never free, so
+    // tilt_refined is false and this branch was skipped entirely - leaving the rotations at the ZERO
+    // that GuessInitialGeometry sets, while the CLI reported them as held at the header value. A
+    // declined tilt and a tilt nobody asked to refine both need the header put back and the rest
+    // refitted around it.
+    if (!tilt_refined) {
         fitted.PoniRot1_rad(geom.GetPoniRot1_rad()).PoniRot2_rad(geom.GetPoniRot2_rad());
         OptimizeGeometry(fitted, spots, calibrant_ring_q, false, &unc);
     }