[iOS Remote] Previously visible subagent and Steps cards disappear after reopening a task

Environment

• Host: ChatGPT/Codex Desktop on Windows
• Client: ChatGPT iOS on iPhone 12, using Remote

Issue

Subagent and structured Steps UI can appear correctly while a remote task is open on iOS, but disappear after leaving and reopening the same task.

This does not require another subagent spawn or update_plan call while the task is closed. The same subagent card/button and Steps UI that were previously visible are no longer shown after reopening.

There is also a second case: if a subagent is spawned while its remote Codex task is not in the foreground on iOS, its card may never appear after returning to the task. I therefore cannot open that subagent thread to see its progress or result, or interact with it from mobile.

Reproduction

1. Open a Desktop task through ChatGPT iOS Remote.
2. While viewing it, let Codex spawn a subagent and create/update its structured Steps list.
3. Confirm the subagent button/card and Steps UI appear.
4. Leave the task or background the iOS app.
5. While it is backgrounded, let Codex spawn another subagent.
6. Reopen the same remote task.
7. Previously visible subagent/Steps UI may be missing, and a subagent spawned while backgrounded may have no card at all.

Expected

Reopening a remote task should rehydrate all spawned subagent threads, their latest progress/results, and the latest structured Steps state, regardless of whether their spawn events were observed live while the task was in the foreground.

Related: #32704, #22773, #28480, #32502