Codex app subagent panel omits agents spawned through nested code-mode calls

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

26.707.41301 (build 5103)

What subscription do you have?

Pro

What platform is your computer?

Darwin 25.5.0 arm64 arm (macOS 26.5.1, build 25F80)

What issue are you seeing?

The Codex app successfully spawns and runs subagents, but they do not appear in the parent thread's Subagents panel when multi_agent_v1__spawn_agent is invoked as a nested tool inside functions.exec.

The backend state is correct: child rollout files exist and thread_spawn_edges links each child to the parent. However, the parent transcript records the spawn as custom_tool_call: exec and contains no collabAgentToolCall: spawnAgent item. The installed app's panel logic derives the subagent list from collabAgentToolCall items, so these successfully created children are omitted.

This is related to #25836, but the failure here is specifically the missing structured event for nested code-mode agent calls, not only an unclickable agent entry.

What steps can reproduce the bug?

1. In the Codex desktop app, ask the agent to spawn a subagent.
2. Let code mode invoke multi_agent_v1__spawn_agent inside functions.exec.
3. Confirm the tool returns an agent ID and nickname and the child completes normally.
4. Open the parent thread's Subagents panel.
5. The spawned child is absent.

Observed diagnostics:

• Parent thread / feedback ID: 019f4b7a-3565-7ca0-943e-9f70729b1e05
• Child threads were persisted and linked through thread_spawn_edges.
• Parent rollout contains custom_tool_call entries named exec.
• Parent rollout contains no collabAgentToolCall entry for the spawn.

What is the expected behavior?

Every successfully spawned child should appear in the parent thread's Subagents panel regardless of whether the spawn tool was called directly or nested through code mode.

The client could either emit a structured collabAgentToolCall event for nested agent operations or reconcile the transcript-derived panel list with persisted thread_spawn_edges.

Additional information

Feedback ID: 019f4b7a-3565-7ca0-943e-9f70729b1e05

App: 26.707.41301 (build 5103)
Codex CLI: 0.144.0-alpha.4

Related: #25836