Desktop app: valid ZIP attachments consistently fail while other file types upload

Summary

In the macOS ChatGPT/Codex desktop app, attaching a small valid ZIP file consistently shows “Upload failed”, while other file types upload successfully.

Environment

• macOS desktop app: 26.818.21641 (build 6849)
• Account type: personal ChatGPT Plus account
• Reproduced after updating from build 6720 to build 6849
• Reproduced after signing out, restarting the app, and signing in again

Steps to reproduce

1. Open a chat or project in the macOS desktop app.
2. Attach a small ZIP archive (approximately 68 KB).
3. The archive contains one binary Garmin FIT activity file.
4. Attempt to submit/upload the attachment.

Expected behavior

The ZIP is accepted as an attachment, or the UI clearly explains that ZIP/FIT content is unsupported.

Actual behavior

The attachment consistently fails with the localized message “Upload failed”. Other non-ZIP files upload normally.

Validation performed

• The ZIP passes a full integrity check with no CRC errors.
• Compression method is standard Deflate.
• The archive contains one file and is far below normal upload-size limits.
• The installed app recognizes application/zip and classifies ZIP content as an archive/folder.
• Renaming the archive is not a viable workaround because the app performs content-based type detection.

Possibly related diagnostic signal

Around the ZIP failure/reload flow, desktop logs repeatedly contain:

GET /backend-api/accounts/{account_id}/settings
401 {"detail":"Must use workspace account for this operation"}

The account identifier has been removed. This request may be unrelated, but it persists in the current build and could indicate that the ZIP-as-folder path is incorrectly invoking workspace-only settings for a personal account.

Workaround

Extracting the archive and providing the contained file through the local workspace avoids the ZIP attachment path.

No user files, account identifiers, or full logs are attached to this report.