VS Code Explorer Model Override #15474

What version of the IDE extension are you using?

26.318.11754

What subscription do you have?

plus

Which IDE are you using?

VS Code

What platform is your computer?

Linux 5.15.167.4-microsoft-standard-WSL2 x86_64 x86_64

What issue are you seeing?

In the VS Code Codex runtime, spawned explorer subagents can ignore the explicit model
override passed in the spawn_agent call.

The parent session requests model="gpt-5.4-mini", but the spawned child thread starts with
turn_context.model = "gpt-5.4".

This makes repo-level subagent configs such as .codex/agents/context-gatherer.toml ineffective
for explorer agents even when the parent agent forwards the configured model explicitly.

What steps can reproduce the bug?

1. Start a parent Codex session in VS Code with default model gpt-5.4.
2. From the parent, spawn a read-only explorer subagent with:
   • agent_type="explorer"
   • model="gpt-5.4-mini"
   • reasoning_effort="medium"
   • fork_context=true
3. Inspect the spawned child session log.

What is the expected behavior?

The child session should start with turn_context.model = "gpt-5.4-mini".

Additional information

• This repro focuses on explorer subagents because the failure is directly confirmed there.
• Repo guidance was already updated to explicitly pass model="gpt-5.4-mini" for
  context-gatherer spawns, so this appears to be a runtime issue rather than a repo-config issue.
• The mismatch is visible in persisted session logs even when the parent call arguments are correct.