[App][Subagents] Child thread opens as a blank white view on macOS and iPhone

Summary

Opening a spawned Codex subagent from the Subagents UI shows the correct child name and header, but the conversation body never renders.

This reproduces on both macOS and iPhone.

Environment

• ChatGPT macOS app: 26.707.91948 (5440)
• Codex CLI/app-server: 0.144.5
• macOS: 26.6 (25G5057c), arm64
• Multi-agent version recorded in the child session: v2

Steps to reproduce

1. Start an interactive Codex task.
2. Spawn a native subagent.
3. Open Subagents.
4. Select the running child on macOS or iPhone.

Expected behavior

The child view displays its prompt, activity, tool calls, status, and final result or error.

Actual behavior

The child header loads, but its content remains blank:

• On macOS, the view stays white with an indefinite OpenAI loading indicator.
• On iPhone, the sheet is completely blank below the header.

The subagent can briefly appear as running and then fail with:

stream disconnected before completion: Encrypted function output content could not be decrypted or decoded.

Even a child whose only task was to stay alive for 10 seconds reproduced the blank view.

Screenshots

<img width="" height="400" alt="Image" src="https://github.com/user-attachments/assets/ca53e947-b3eb-4f9a-b7b2-07aec5265d5a" />

<img width="" height="400" alt="Image" src="https://github.com/user-attachments/assets/56253b96-f46d-47e5-84a5-187ed719aea0" />

Related issues

• #15306
• #16358
• #24475
• #33267