Windows desktop: message input field disappears for one specific chat while messages still sync from mobile

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

26.908.9136.0

What subscription do you have?

Business

What platform is your computer?

Microsoft Windows 11, x64, build 26200

What issue are you seeing?

The message input field is completely missing in one specific existing chat in the Windows desktop app.

The conversation history, assistant responses, and generated PDF attachments are displayed normally. Other chats still show a working message input field.

The same affected chat can be continued from the mobile app. Messages sent from the phone synchronize correctly and appear in the Windows app, but the message input field remains missing there.

This indicates that the conversation and synchronization are still working. Only the message input field for this particular chat fails to appear in the Windows app.

What steps can reproduce the bug?

I cannot reproduce this issue deterministically because I do not know what originally caused the message input field to disappear.

I can only describe the current, persistent state:

1. One specific chat has no message input field in the Windows desktop app.
2. Other chats still display their input fields normally.
3. Switching to another chat and returning does not restore the field.
4. Reloading the Windows app does not restore the field.
5. Closing and restarting the Windows app does not restore the field.
6. The affected chat remains usable from the mobile app.
7. Messages sent from mobile synchronize to the Windows app, but the message input field remains missing.

The original trigger is unknown.

Actual behavior

The affected chat can be read and receives synchronized messages, but it cannot be continued from the Windows app because its message input field is missing.

What is the expected behavior?

Every active chat that can be continued from another client should display a working message input field in the Windows app.

If a chat is intentionally read-only, the app should explain why instead of silently hiding the field.

Additional information

Observed on 2026-09-18.

The affected chat has a longer history and contains generated PDF attachments. This may be relevant, but the cause is unknown.

The problem affects only one chat, not the entire application.

Possibly related: #43278 reports a disappearing composer on macOS after a transient conversation_inaccessible error. This report is different because it affects Windows, persists after switching chats, reloading, and restarting, while messages sent from mobile continue to synchronize into the affected chat.

No conversation contents, account identifiers, local paths, chat IDs, session IDs, or screenshots containing private information are included.

No source files, tests, or entry points are identified. Start by reproducing the persistent missing composer in the Windows desktop app and compare the affected chat with other chats; review related issue #43278 for context. Done means the affected chat displays a working input field, or clearly explains why it is read-only, without breaking message synchronization.