rugnux: fit the profile radius from the strongest spots too

Same defect as the mosaicity in 2c94f3013, in the same file's sibling fit. The
profile radius is an RMS of the excitation error over whatever spots were kept,
and weaker spots sit further off the Ewald sphere, so it grows with the depth of
the list: measured over a 150 -> unlimited spot budget it rises ~60%, and on a
clean dataset as much as on a hard one, so this is general rather than something
one awkward crystal provoked. That made it a function of --max-spots, which is
an indexing budget, rather than of the crystal.

Its one consumer treats it as a membership gate (ewald_dist_cutoff is twice it)
where reflections at the cutoff carry near-zero partiality and are removed
downstream anyway, so the integrated data barely notices: with the mosaicity
already pinned, the partial count moves 0.2% across a 34% change in the radius.
It is also reported per image as a diagnostic, though, and a number that slides
with an unrelated setting is misleading to anyone comparing two runs - and it
would stop being benign the moment anything used it as a width rather than a
gate.

Battery over 37 crystals: no space group changes, 36 of 37 bit-identical, no
failures, one crystal marginally better.

Also in the comparison script: report XDS's mosaicity next to rugnux's. XDS has
two and they are not interchangeable - CORRECT.LP's REFLECTING_RANGE_E.S.D. is
post-refined, while INTEGRATE.LP's per-batch SIGMAR is its integration-stage
estimate, and the two differ by up to 2.3x. The XDS cell now prints both as
postrefined|MLE so a per-image estimate is compared against the one measured the
same way. Fixes a scoping bug in the same addition where every crystal read the
last directory's INTEGRATE.LP.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

image_analysis/indexing/FitProfileRadius.cpp

@@ -11,7 +11,20 @@ std::optional<float> FitProfileRadius(const std::vector<SpotToSave>& spots,
     double sum_bw_var = 0.0;      // energy-bandwidth contribution to subtract out
     int count = 0;
 
-    for (const auto &s: spots) {
+    // Fitted from the strongest spots only. This is an RMS over whatever spots were kept, and weaker
+    // spots sit further off the Ewald sphere, so it grows with the depth of the list: measured over a
+    // 150 -> unlimited spot budget it rises ~60% on both a hard and a clean rotation dataset. That
+    // made it a function of the INDEXING budget (--max-spots) rather than of the crystal. Its one
+    // consumer treats it as a membership gate (ewald_dist_cutoff = 2x it), where reflections at the
+    // cutoff carry ~zero partiality, so the integrated data barely moved (0.2% of partials across
+    // that range) - but it is also reported per image as a diagnostic, where a number that slides
+    // with an unrelated setting is simply misleading. FilterSpotsByCount leaves the list
+    // strongest-first, so taking the head selects the spots a smaller --max-spots would.
+    constexpr size_t PROFILE_RADIUS_FIT_SPOTS = 250;
+    const size_t n_fit = std::min(spots.size(), PROFILE_RADIUS_FIT_SPOTS);
+
+    for (size_t si = 0; si < n_fit; ++si) {
+        const auto &s = spots[si];
         if (!s.indexed)
             continue;
         sum_squares += static_cast<double>(s.dist_ewald_sphere) * s.dist_ewald_sphere;