From b1a3a5dd465e0b91b3f3f047993f7370b7922435 Mon Sep 17 00:00:00 2001
From: Thor <thor@joerger.dev>
Date: Thu, 23 Apr 2026 12:15:25 +0200
Subject: [PATCH] Fix GetMinMergedCell for cells spanning all columns and
 multiple rows

When a single cell spans all columns (MergeRight = columnCount - 1) and
more than one row (MergeDown >= 1), GetMinMergedCell() throws
InvalidOperationException because the condition

    resultRowIndex + cell.MergeDown == row

simplifies to MergeDown == 0, which the origin cell (MergeDown >= 1) does
not satisfy. All other cells in that row are excluded because they are not
in _mergedCells (they are covered by the merge).

Fix: add a fallback loop that finds the cell with the minimum MergeDown
value in _mergedCells for the given row. This matches the behaviour of
GetMinMergedCellOriginal() which handles this case correctly.
---
 .../Rendering/TableRenderer.cs                | 31 +++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/src/foundation/src/MigraDoc/src/MigraDoc.Rendering/Rendering/TableRenderer.cs b/src/foundation/src/MigraDoc/src/MigraDoc.Rendering/Rendering/TableRenderer.cs
index a28b6406..a233a635 100644
--- a/src/foundation/src/MigraDoc/src/MigraDoc.Rendering/Rendering/TableRenderer.cs
+++ b/src/foundation/src/MigraDoc/src/MigraDoc.Rendering/Rendering/TableRenderer.cs
@@ -903,6 +903,37 @@ Cell GetMinMergedCell(int row)
                     return cell;
                 }
             }
+
+            // Fallback: all cells in this row begin multi-row spans (MergeDown > 0),
+            // so no cell satisfies `resultRowIndex + MergeDown == row`.
+            // This occurs when a single cell spans all columns and more than one row
+            // (e.g. MergeRight = columnCount - 1, MergeDown >= 1).
+            // Find the cell with the minimum MergeDown instead —
+            // this matches the behaviour of GetMinMergedCellOriginal.
+            int minMergeDown = int.MaxValue;
+            Cell? minCell = null;
+            for (int idx = 0; idx < clsCount; idx++)
+            {
+                var cell = resultRow[idx];
+                if (!_mergedCells.Contains(cell))
+                    continue;
+                if (cell.MergeDown < minMergeDown)
+                {
+                    minMergeDown = cell.MergeDown;
+                    minCell = cell;
+                    if (minMergeDown == 0)
+                        break; // Can't get better.
+                }
+            }
+            if (minCell is not null)
+            {
+#if DEBUG
+                Debug.Assert(originalResult.Row!.Index + originalResult.MergeDown ==
+                             minCell.Row!.Index + minCell.MergeDown);
+#endif
+                return minCell;
+            }
+
             throw new InvalidOperationException("GetMinMergedCell: Unexpected problem #1");
         }