Bragg prediction: say so when a frame overflows the prediction buffer

Found while chasing a 12% run-to-run spread in the merged reflection count of one
crystal. The GPU kernels claim output slots with an atomicAdd and, on overflow,
undid the increment with an atomicSub - so the counter saturated at the capacity
and the host could not tell a full buffer from an overflowing one. Which
reflections survived was then decided by CUDA block scheduling and changed every
run. Measured on that dataset: every frame predicts 23000-44000 against a 20000
buffer, and the spread reached the merged output (161591 / 165193 / 166110 /
166479 unique across four runs of the same command). Single-threaded runs diverge
too - this is entirely GPU-side.

Stop clamping the counter, so the true number predicted reaches the host, and
warn once per predictor when it exceeds the buffer. Which reflections are kept is
unchanged: making that reproducible means deciding what to keep when a frame
predicts more than the pipeline carries, and the obvious answers are worse - the
capacity is not the real limit, kPredictionOutput (10000, selected by smallest
excitation error) is, and on this crystal both a bigger buffer and a strided
selection collapse the merge, because the rotation combine rebuilds fulls from
exactly the partials that a smallest-excitation-error cut throws away.

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

image_analysis/bragg_prediction/BraggPrediction.cpp

@@ -4,9 +4,21 @@
 #include <algorithm>
 
 #include "../../common/JFJochMath.h"
+#include "../../common/Logger.h"
 #include "BraggPrediction.h"
 #include "../bragg_integration/SystematicAbsence.h"
 
+void BraggPrediction::ReportOverflow(int predicted) {
+    if (overflow_reported)
+        return;
+    overflow_reported = true;
+    Logger("BraggPrediction").Warning(
+        "A frame predicted {} reflections but the buffer holds {} - the ones kept are whichever the GPU "
+        "wrote first, so this dataset does NOT process reproducibly. Results will differ between runs. "
+        "The cell is large enough that the prediction cap no longer fits it.",
+        predicted, kPredictionCapacity);
+}
+
 int BraggPrediction::TruncateToOutput(int count) {
     if (count <= kPredictionOutput)
         return count;