Subagent spawn lines show raw thread IDs instead of readable labels

Summary

Subagent spawn lines in Codex CLI show raw GUID-like thread IDs instead of readable labels.

Environment

• Codex CLI version: 0.134.0
• OS: Windows
• Terminal: PowerShell

Minimal repro

1. Start Codex:

``text
codex
``

1. Paste this prompt:

```text
Spawn 2 subagents and wait for both.

• Agent 1: list the top-level files in the current repo.
• Agent 2: list the top-level directories in the current repo.

Then summarize both results.
```

1. Watch the main thread activity feed as the subagents are created.

Actual result

The activity feed shows raw GUID-like / thread-ID values in the spawn lines, for example:

• Spawned 019e6d16-29c2-7a40-b1bb-4d6f6dbf2bd4 (gpt-5.4-mini xhigh)
  └ Review the current Talio workspace as a PR review focused on correctness bugs, regressions, edge cases, and contract mismatches.

• Spawned 019e6d16-2aa4-74e3-a234-18fbc9c40142 (gpt-5.4-mini xhigh)
  └ Review the current Talio workspace as a PR review focused on races, async hazards, ordering, concurrency, and idempotency risks.

Expected result

Newly spawned subagents should display a readable label immediately, not only a raw thread ID.

Secondary symptom

If I use /agent, open the subagent, and then return to the main agent, the label may render correctly afterward.

Notes

• This looks like a UI/rendering issue rather than a functional failure of the subagent itself.
• The problem appears at subagent spawn time and does not seem repo-specific.