[Spreadsheets] artifact-tool 2.8.59 turns no-fill cells with empty color nodes solid black

What version of the Codex App are you using (From “About Codex” dialog)?

26.901.51231 (build 8109); bundled runtime 26.905.11957

What subscription do you have?

Not specified; reproducible directly in the local bundled runtime

What platform is your computer?

macOS 26.4.1, arm64; Node.js 24.19.0; @oai/artifact-tool 2.8.59

What issue are you seeing?

Importing an XLSX whose default fill is patternType="none" with empty and children produces an opaque black worksheet preview, making black text invisible. An unedited import/export round trip also changes the fill to patternType="solid".

A synthetic 2-column, 3-row workbook reproduces this without business data. The control with no color children renders normally. PNG black pixels have RGBA (0,0,0,255), so this is not transparent-image viewer compositing.

Computed style reports pattern.patternType:1 for the control and pattern.patternType:2 for the trigger. Exported trigger fill becomes <x:patternFill patternType="solid" />.

What steps can reproduce the bug?

1. Create a small workbook using the bundled package:

import { Workbook, SpreadsheetFile } from '@oai/artifact-tool';
const wb = Workbook.create();
const s = wb.worksheets.add('Sheet1');
s.getRange('A1:B3').values = [['Text','Example'],['Arial 123','Sample A'],['More text','Sample B']];
s.getRange('A1:B3').format.columnWidth = 24;
s.getRange('A1:B3').format.font = {name:'Arial',size:11,color:'#000000'};
wb.recalculate();
await (await SpreadsheetFile.exportXlsx(wb)).save('base.xlsx');

2. Copy base.xlsx to trigger.xlsx, replacing only the first patternFill in xl/styles.xml within the ZIP. Preserve the namespace prefix (x: in my test).

Control:

<x:patternFill patternType="none" />

Trigger:

<x:patternFill patternType="none"><x:fgColor/><x:bgColor/></x:patternFill>

3. Import, render and export without editing any cells:

import fs from 'node:fs/promises';
import { FileBlob, SpreadsheetFile } from '@oai/artifact-tool';
const wb = await SpreadsheetFile.importXlsx(await FileBlob.load('trigger.xlsx'));
console.log((await wb.inspect({kind:'computedStyle',sheetId:'Sheet1',range:'B2',maxChars:2000})).ndjson);
const png = await wb.render({sheetName:'Sheet1',range:'A1:B3',scale:1.5});
await fs.writeFile('preview.png',new Uint8Array(await png.arrayBuffer()));
wb.recalculate();
await (await SpreadsheetFile.exportXlsx(wb)).save('roundtrip.xlsx');

4. Compare preview.png and xl/styles.xml in roundtrip.xlsx for both variants. Control stays white/no-fill; trigger becomes black/solid.

What is the expected behavior?

No-fill semantics should take precedence over irrelevant color children: patternType="none" should render with the normal worksheet background and remain none after import/export.

Additional information

Test matrix:

Input patternFill	Preview	Round-trip XML
none, no color children	White/readable	none
none, empty fgColor/bgColor	Opaque black	solid, no explicit color
none, both colors rgb=00000000	Opaque black	solid, fgColor rgb=FF000000
none, foreground red/background white	White, but semantics changed	solid, fgColor rgb=FFFFFFFF
Empty patternFill, no attributes/children	White/readable	none

Workaround: remove fgColor/bgColor only from fills explicitly marked patternType=none before importing. This restores rendering and round-trip no-fill semantics.

Setting range.format.fill=null after import did not resolve the affected workbook. An explicit white fill restores text inside that range but changes the intended formatting and leaves affected cells outside the range black. Arial and SimSun text are readable once the fill is normalized. Native Excel displays no-fill normally in a structurally valid workbook.

This appears to be an import/style-conversion defect, not solely a PNG rendering issue. Package internals were not inspected, so the exact implementation cause is not asserted. Please route to the bundled spreadsheet/artifact-tool runtime maintainers. No private workbook, business data, or local user paths are included in this report.

Run the provided Node.js reproduction with @oai/artifact-tool 2.8.59, comparing the control and trigger workbooks. Inspect xl/styles.xml before and after the import/export round trip and compare the rendered preview. Done means patternType="none" with empty color nodes renders as no fill and remains none in the exported workbook.