Nested hybrid grid: reject active-cell-only grids and fix setCellResultIndex assert

Active-cell grids report a fixed total cell count, so appended LGR cells overflowed the active cell info array. Return an error instead, and assert on the reservoir cell index.

ApplicationLibCode/ReservoirDataModel/RigActiveCellInfo.cpp

@@ -76,7 +76,7 @@ ActiveCellIndex RigActiveCellInfo::cellResultIndex( ReservoirCellIndex reservoir
 //--------------------------------------------------------------------------------------------------
 void RigActiveCellInfo::setCellResultIndex( ReservoirCellIndex reservoirCellIndex, ActiveCellIndex reservoirCellResultIndex )
 {
-    CAF_ASSERT( reservoirCellResultIndex.value() < m_reservoirCellToActiveCell.size() );
+    CAF_ASSERT( reservoirCellIndex.value() < m_reservoirCellToActiveCell.size() );
 
     m_reservoirCellToActiveCell[reservoirCellIndex.value()] = reservoirCellResultIndex;
 }

ApplicationLibCode/ReservoirDataModel/RigNestedHybridGridReconstructor.cpp

@@ -20,6 +20,7 @@
 
 #include "RiaLogging.h"
 
+#include "RigActiveCellGrid.h"
 #include "RigActiveCellInfo.h"
 #include "RigCaseCellResultsData.h"
 #include "RigCell.h"
@@ -70,7 +71,15 @@ bool RigNestedHybridGridReconstructor::reconstruct( RigEclipseCaseData* caseData
 
     if ( !caseData || !caseData->mainGrid() ) return setError( "No grid data." );
 
-    RigMainGrid* grid      = caseData->mainGrid();
+    RigMainGrid* grid = caseData->mainGrid();
+
+    // Active-cell-only grids keep cells in a sparse map and report a fixed total cell count, so
+    // appending LGR cells is not supported and would write out of bounds.
+    if ( dynamic_cast<RigActiveCellGrid*>( grid ) )
+    {
+        return setError( "Reconstruction is not supported for grids with only active cells loaded." );
+    }
+
     const size_t cellCount = grid->cellCount();
 
     if ( input.refine.size() != cellCount )