Codex desktop workbook preview panel goes blank with PopcornElectronWorkbookPanel worker error

Summary

In the Codex desktop app on macOS, opening a generated .xlsx artifact in the right-side workbook preview panel can leave the panel blank/empty. Restarting Codex does not recover the preview for the same file.

The app log shows repeated Worker runtime error failures from PopcornElectronWorkbookPanel.

Environment

• Codex desktop app: 26.623.70822 (CFBundleVersion 4559)
• Bundled Codex CLI: codex-cli 0.142.4
• macOS: 26.3.1 (a), build 25D771280a
• Thread mode: local desktop app

Repro

1. In the Codex desktop app, ask Codex to generate an .xlsx artifact.
2. Click/open the spreadsheet artifact card so it appears in the right-side preview panel.
3. The panel opens a spreadsheet-like shell, but the workbook content does not render.
4. Quit and reopen Codex.
5. Click/open the same .xlsx artifact again.

Expected

The workbook preview panel renders the workbook sheets so the user can inspect cells and ask Codex questions about specific areas.

Actual

The workbook preview panel remains blank/empty. The artifact can still be opened externally, and a separate openpyxl-based preview script can read the workbook successfully.

The generated workbook in this repro was small, around 9 KB, with four sheets and no formula errors in a separate scan, so this does not appear to be a large-file issue.

Relevant log excerpt

2026-07-08T11:53:08.365Z error [electron-message-handler] [desktop-notifications][global-error] Error: Worker runtime error
    at He.onError (app://-/assets/PopcornElectronWorkbookPanel-DEXqsHf5.js:8:413749)
    at #i (app://-/assets/remote-text-edit-session-0olsg5KH.js:1:49007)
    at He.worker.onerror (app://-/assets/remote-text-edit-session-0olsg5KH.js:1:48006) rendererWebContentsId=1 rendererWindowAppearance=primary rendererWindowFocused=true rendererWindowId=1 rendererWindowVisible=true

2026-07-08T11:53:19.914Z error [electron-message-handler] [desktop-notifications][global-error] Error: Worker runtime error
    at He.onError (app://-/assets/PopcornElectronWorkbookPanel-DEXqsHf5.js:8:413749)
    at #i (app://-/assets/remote-text-edit-session-0olsg5KH.js:1:49007)
    at He.worker.onerror (app://-/assets/remote-text-edit-session-0olsg5KH.js:1:48006) rendererWebContentsId=1 rendererWindowAppearance=primary rendererWindowFocused=true rendererWindowId=1 rendererWindowVisible=true

Notes

• I did not attach the source workbook because it contains user business data.
• The same workbook can be read by openpyxl, and exporting an HTML/CSV preview works as a local workaround.
• This looks like a workbook preview worker/rendering failure rather than a model/context-size issue.