[Windows App] Native PDF side-pane annotation controls missing after update (26.915.3509)

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

26.915.3509. Windows package version: 26.915.3509.0, verified from the installed/running application package rather than the About dialog.

What subscription do you have?

Not captured.

What platform is your computer?

Windows, x64. Chinese-language UI. Observed September 18, 2026, Asia/Shanghai time zone.

What issue are you seeing?

The native PDF preview in the desktop app's side pane has no visible annotation/comment entry point. The user reports that PDF annotations were available before a recent update and are now missing. The exact first affected version and cause have not been established.

The user-provided screenshot shows a normally rendered 46-page PDF, with the filename menu, page navigation (2/46), zoom (244%), and download controls, but no annotation control.

This blocks the intended workflow: read a generated report in the GPT/Codex side pane, select passages, add comments, and ask the assistant to revise the report. The user specifically needs this workflow inside the app.

What steps can reproduce the bug?

Observed sequence on the affected installation:

1. Generate a local PDF in a Codex task and open it in the native PDF side-pane preview.
2. Navigate to a body-text page.
3. Look for the annotation/comment entry point.
4. Observe that the normal viewing controls are present but the annotation control is absent.

This is a report from one affected installation, not a claim that it reproduces on every account or machine.

What is the expected behavior?

Provide a visible, usable native PDF annotation control in the side pane, allowing the user to attach comments to the report and request changes. If availability is intentionally conditional, explain that in the UI and provide a supported recovery path.

Additional information

• The affected PDF was checked locally: 46 pages, searchable text, no encryption, no PDF permission restrictions, and no read-only file attribute.
• The same document accepts Chinese comments and saves/reopens successfully in a separate PDF.js viewer. That workaround does not restore the native annotation entry point.
• Read-only inspection of the installed client indicates that PDF annotation functionality still exists and its availability is conditional. Runtime feature configuration was not inspected, so no specific gate or root cause is asserted.
• Related issue: #26931 describes annotation availability differing by opening route on macOS. This report concerns a currently affected Windows build; whether the underlying cause is the same is unknown.
• The screenshot's visible controls are described above in text. The original report, private paths, account identifiers, and session logs are not included.

Please investigate a possible regression or availability/configuration issue and provide a supported way to restore native PDF annotations.

Start by reproducing the missing annotation control in the Windows native PDF side-pane preview on build 26.915.3509.0, then inspect the app's conditional PDF annotation availability and configuration. Done means the side pane provides a visible annotation entry point and the user can attach comments to a PDF and reopen the saved document.