fix: derive DataGrid2 column names from attribute or caption

Column names were always generated as sequential identifiers (col1,
col2, ...) in DESCRIBE PAGE output. Now derives semantic names from
the column's bound attribute or caption text, falling back to col%d
only when neither is available.

Author: engalar

mdl/executor/cmd_pages_describe_output.go

@@ -354,10 +354,9 @@ func (e *Executor) outputWidgetMDLV3(w rawWidget, indent int) {
 					}
 					fmt.Fprintf(e.output, "%s  }\n", prefix)
 				}
-				// Output columns
+				// Output columns — derive name from attribute or caption, fall back to col%d
 				for i, col := range w.DataGridColumns {
-					// Generate synthetic column name since Mendix doesn't store it
-					colName := fmt.Sprintf("col%d", i+1)
+					colName := deriveColumnName(col, i)
 					e.outputDataGrid2ColumnV3(prefix+"  ", colName, col)
 				}
 				fmt.Fprintf(e.output, "%s}\n", prefix)
@@ -576,6 +575,31 @@ func (e *Executor) outputWidgetMDLV3(w rawWidget, indent int) {
 	}
 }
 
+// deriveColumnName produces a semantic column name from the column's attribute
+// or caption. Falls back to "col%d" when neither is available.
+func deriveColumnName(col rawDataGridColumn, index int) string {
+	if col.Attribute != "" {
+		// Use the short attribute name (last segment after dot)
+		parts := strings.Split(col.Attribute, ".")
+		return parts[len(parts)-1]
+	}
+	if col.Caption != "" {
+		// Sanitize caption to a valid identifier: keep alphanumeric, replace rest with underscore
+		sanitized := strings.Map(func(r rune) rune {
+			if r >= 'a' && r <= 'z' || r >= 'A' && r <= 'Z' || r >= '0' && r <= '9' || r == '_' {
+				return r
+			}
+			return '_'
+		}, col.Caption)
+		// Trim leading/trailing underscores and collapse multiples
+		result := strings.TrimFunc(sanitized, func(r rune) bool { return r == '_' })
+		if result != "" {
+			return result
+		}
+	}
+	return fmt.Sprintf("col%d", index+1)
+}
+
 // outputDataGrid2ColumnV3 outputs a single DataGrid2 column in V3 MDL syntax.
 func (e *Executor) outputDataGrid2ColumnV3(prefix, colName string, col rawDataGridColumn) {
 	// Build the main column properties