Allow spawn_agent to select Normal or Fast mode per subagent

What variant of Codex are you using?

App

What feature would you like to see?

I would like the spawn_agent tool to support selecting a child agent's speed. Right now, it seems to inherit the service_tier setting from config.toml.

Current schema:

spawn_agent({
  task_name: string,
  message: string,
  fork_turns?: "none" | "all" | "<positive integer>",
  model?: "gpt-5.6-sol" | "gpt-5.6-terra",
  reasoning_effort?: "low" | "medium" | "high" | "xhigh" | "max" | "ultra"
})

Please extend the schema with a field such as this, so a manager thread can spawn sub agents with different speed settings:

service_tier?: "default" | "priority"

Additional information

_No response_