Preserve QExcell gridline visibility in XLSX

src/io/excellOffice.test.ts

@@ -27,6 +27,7 @@ import {
   worksheetXmlToHyperlinks,
   worksheetXmlToMergedCells,
   worksheetXmlToRowHeights,
+  worksheetXmlToShowGridLines,
   worksheetXmlToTabColor,
   xlsxStylesXmlToCellFormatTable,
   xlsxThemeXmlToColors,
@@ -650,6 +651,43 @@ describe("excellOffice OOXML helpers", () => {
     expect(imported.sheets[0].frozenPane).toEqual({ columns: 1, rows: 1, topLeftCell: "B2", activePane: "bottomRight" });
   });
 
+  it("читает и записывает скрытие сетки листа XLSX через sheetView showGridLines", async () => {
+    expect(
+      worksheetXmlToShowGridLines({
+        worksheet: {
+          sheetViews: {
+            sheetView: { showGridLines: "0" }
+          }
+        }
+      })
+    ).toBe(false);
+    expect(buildSheetViewsXml(undefined, false)).toBe('<sheetViews><sheetView workbookViewId="0" showGridLines="0"/></sheetViews>');
+    expect(buildSheetViewsXml({ rows: 1 }, false)).toBe(
+      '<sheetViews><sheetView workbookViewId="0" showGridLines="0"><pane ySplit="1" topLeftCell="A2" activePane="bottomLeft" state="frozen"/></sheetView></sheetViews>'
+    );
+
+    const blob = await exportXlsxBlob({
+      id: "book-1",
+      title: "Grid lines.xlsx",
+      updatedAt: "2026-06-01T00:00:00.000Z",
+      activeSheet: "sheet-1",
+      sheets: [
+        {
+          id: "sheet-1",
+          name: "Grid",
+          showGridLines: false,
+          cells: { A1: "No grid" }
+        }
+      ]
+    });
+    const zip = await JSZip.loadAsync(await blob.arrayBuffer());
+    const sheetXml = (await zip.file("xl/worksheets/sheet1.xml")?.async("string")) ?? "";
+    const imported = await importXlsxFile(new File([blob], "Grid lines.xlsx", { type: blob.type }));
+
+    expect(sheetXml).toContain('<sheetViews><sheetView workbookViewId="0" showGridLines="0"/></sheetViews>');
+    expect(imported.sheets[0].showGridLines).toBe(false);
+  });
+
   it("читает и записывает автофильтр XLSX через autoFilter ref", async () => {
     expect(
       worksheetXmlToAutoFilter({