Codex desktop: xlsx preview reports "aren't supported yet" for every workbook after 26.715.70719 (build 5650)

Environment

• Codex desktop (macOS) 26.715.70719 / build 5650 (Sparkle-updated Jul 21 ~17:00 UTC)
• macOS 15.6 (Darwin 24.6.0), Apple Silicon

What happens
Clicking any .xlsx in the workspace shows:

Excel spreadsheet previews aren't supported yet Open this file in another app to view it

No preview panel opens, and unlike #31749 there is no blank panel — the app declines the file type before attempting to render. Notably, the "aren't supported yet" phrasing reads like feature-rollout copy rather than an error state, which fits a feature gate being switched off.

What I expected
The workbook preview panel, which worked on this machine through ~Jul 19 (previous builds; Sparkle update history shows 5440 → 5628 → 5650).

Evidence this is app-side, not file-side
I tested a controlled matrix — every one of these refuses with the same message:

1. A blank single-sheet workbook freshly generated with openpyxl
2. A plain-values workbook, no styling
3. A workbook with multiple sheets, an Excel Table, and freeze panes
4. Pre-existing project workbooks that previewed fine in earlier builds
5. A brand-new file authored directly in Microsoft Excel for Mac

All five open normally in Excel and load cleanly with openpyxl. macOS file-type resolution is healthy (mdls reports org.openxmlformats.spreadsheetml.sheet; the system Quick Look generator claims the UTI), so this is not an OS registration issue.

Additional observations

• App logs (~/Library/Logs/com.openai.codex/...) from today contain no workbook/preview entries at all when clicking an xlsx — consistent with the feature being gated off rather than crashing.
• The PopcornElectronWorkbookPanel assets still ship in the current build's app.asar.
• Possibly related: #31749 (workbook panel blank with PopcornElectronWorkbookPanel worker error, filed Jul 9). If the panel was intentionally disabled pending that fix, a changelog note would save users a lot of file-side debugging.

Questions

1. Is xlsx preview intentionally feature-gated off in current builds? If so, is re-enablement tied to a fix for #31749?
2. If not intentional — is there a workaround (setting, flag, channel) to restore it?