Fix combined view column alignment

MainWindow.cs

@@ -1081,16 +1081,59 @@ private Control BuildFilePanel(TextBox tb, Button browse, ComboBox cb, StackPane
                 break;
 
             default:
-                headers = main.Columns;
+                // Build a union of both schemas. Columns with the same header are
-                foreach (var r in result.Matches) data.Add(r);
+                // aligned; B-only columns get their own position in the result.
+                headers = new List<string>(main.Columns);
+                var mainColumnMap = Enumerable.Range(0, main.Columns.Count).ToArray();
+                var secondaryColumnMap = new int[sec.Columns.Count];
+                var matchedSecondaryColumns = new HashSet<int>();
+
+                for (int b = 0; b < sec.Columns.Count; b++)
+                {
+                    int matchingMain = -1;
+                    for (int a = 0; a < main.Columns.Count; a++)
+                    {
+                        if (!matchedSecondaryColumns.Contains(a) &&
+                            string.Equals(main.Columns[a].Trim(), sec.Columns[b].Trim(), StringComparison.OrdinalIgnoreCase))
+                        {
+                            matchingMain = a;
+                            break;
+                        }
+                    }
+
+                    if (matchingMain >= 0)
+                    {
+                        secondaryColumnMap[b] = matchingMain;
+                        matchedSecondaryColumns.Add(matchingMain);
+                    }
+                    else
+                    {
+                        var header = sec.Columns[b];
+                        if (headers.Contains(header, StringComparer.OrdinalIgnoreCase))
+                            header = $"B: {header}";
+                        secondaryColumnMap[b] = headers.Count;
+                        headers.Add(header);
+                    }
+                }
+
+                string[] CombineRows(string[] rowA, string[] rowB)
+                {
+                    var combined = new string[headers.Count];
+                    Array.Fill(combined, "");
+                    for (int a = 0; a < mainColumnMap.Length && a < rowA.Length; a++)
+                        combined[mainColumnMap[a]] = rowA[a];
+                    for (int b = 0; b < secondaryColumnMap.Length && b < rowB.Length; b++)
+                        combined[secondaryColumnMap[b]] = rowB[b];
+                    return combined;
+                }
+
+                foreach (var pair in result.Pairs)
+                    data.Add(CombineRows(pair.RowA, pair.RowB));
                 sources = new List<string>();
-                foreach (var _ in result.Matches) sources.Add("A");
+                foreach (var _ in result.Pairs) sources.Add("A+B");
                 foreach (var r in result.OnlySecondary)
                 {
-                    var row = new string[main.Columns.Count];
+                    data.Add(CombineRows(Array.Empty<string>(), r));
-                    Array.Fill(row, "");
-                    for (int c = 0; c < row.Length && c < r.Length; c++) row[c] = r[c];
-                    data.Add(row);
                     sources.Add("B");
                 }
                 break;