[macOS Desktop][turn/steer] Entire completed assistant message disappears from transcript

App and platform

ChatGPT/Codex desktop 26.810.52044 on macOS.

Issue

A completed assistant response can disappear from the visible desktop transcript after follow-up messages are steered into an active turn.

In the observed session, the assistant produced a substantial final response after several follow-ups were sent while it was working. When the conversation continued, that completed response was no longer visible. Asking the assistant to print it again recovered the content. This has happened repeatedly with steered follow-ups.

Steps to reproduce

1. Open an existing desktop chat.
2. Ask for a response that requires a longer-running turn.
3. While the turn is active, send one or more follow-up messages.
4. Let the assistant finish and display its final response.
5. Continue the conversation.
6. Observe that the prior completed response can disappear from the visible transcript.

Expected behavior

Steering should update the active turn while every completed assistant response remains visible in chronological order.

Actual behavior

The follow-ups are handled, but a substantial completed assistant response disappears from the visible transcript and must be regenerated.

Distinguishing details

• The missing object is the entire completed assistant message, not a local-file link or an output directive.
• No PDF, file citation, :codex-file-citation{...}, or generated local artifact is involved.
• The observed trigger is one or more follow-ups delivered to an active turn through turn/steer.
• The app log records method=turn/steer; the same log window then contains repeated ResizeObserver loop completed with undelivered notifications and Received turn/started|completed for unknown conversation messages. Conversation identifiers are omitted.

Duplicate review

This is not #38211. That issue is specific to a Windows local-PDF file citation disappearing while the underlying assistant message and PDF remain. This report concerns a complete assistant response disappearing on macOS after steering, with no file citation involved.

Other superficially related reports also have different triggers and persisted states: #28751 concerns empty messages saved after resuming an older Windows thread; #26872 concerns content located in another thread; #34255 concerns the model selector disappearing after switching chats; and #33558 concerns duplicate submit dispatches.

Impact

This makes the desktop transcript unreliable for long technical deliverables and creates an apparent data-loss condition.

Start by reproducing the disappearing transcript entry on macOS with follow-ups sent through turn/steer, then inspect the turn/steer handling and transcript update path. Use the app log around turn/started, turn/completed, and the repeated unknown-conversation messages to trace the affected conversation. Done means completed assistant responses remain visible in chronological order after steered turns.