Support first-class main-session agent/role presets with skill scoping

Summary

Codex should support first-class role/agent presets for the main session, not just top-level --profile config overrides or isolated CODEX_HOME workarounds.

A role should be able to define things like:

• system/developer instructions
• allowed/disallowed tools
• preloaded skills
• model / provider / profile defaults
• optional approval / sandbox defaults

and then be selectable directly at startup, for example:

codex --agent frontend
codex --agent backend
codex --agent reviewer

Problem

Today, --profile appears to be a config/profile selector, not a true role/agent definition mechanism.

That means there is currently no clean built-in way to express a setup like:

• frontend agent can use frontend/UI skills
• backend agent can use backend/server skills
• reviewer agent can use review-focused skills and prompts

without falling back to heavier workarounds like separate CODEX_HOME directories.

Using separate CODEX_HOME roots is functional but awkward because it can also split:

• config state
• installed skills
• local history/session state
• auth and other user-local data

That is much heavier than “start the same Codex, but as a different role”.

Why this matters

This is useful even for single-user workflows, not only multi-agent orchestration.

Typical usage:

• one terminal starts a frontend role
• another starts a backend role
• both belong to the same overall user/workspace flow
• but each should have different instructions, skill preload, and capability surface

Claude Code already exposes a much more direct version of this idea via --agent / custom agents. Codex currently feels noticeably less ergonomic for this specific workflow.

Proposed UX

Any of these would help, with a strong preference for the first two:

Option 1: first-class top-level agents

Allow config like:

[agents.frontend]
description = "Frontend/UI specialist"
prompt = "You are a frontend specialist..."
skills = ["frontend-skill", "ui-review"]
tools = ["Read", "Edit", "Write", "Bash"]
profile = "frontend"

[agents.backend]
description = "Backend specialist"
prompt = "You are a backend specialist..."
skills = ["backend-skill"]
tools = ["Read", "Edit", "Write", "Bash"]
profile = "backend"

Then:

codex --agent frontend
codex --agent backend

Option 2: role presets that extend profiles

Keep profiles for ordinary config, but add a higher-level role layer that can also bind skills, prompts, and tool restrictions.

Option 3: make skills profile-scoped

If Codex does not want a full agent abstraction yet, allowing profiles.<name>.skills (or equivalent) would still close a large part of the gap.

Expected behavior

• A role should be selectable at startup without switching to a different CODEX_HOME
• Different roles should be able to preload different skills
• Different roles should be able to set different instructions / tool restrictions
• Roles should compose cleanly with existing profiles
• Session/history storage should remain in the same normal Codex environment unless the user explicitly wants full separation

Non-goal

This request is not asking for full background subagent orchestration by itself.
It is mainly about making “start Codex as role X” a first-class concept for the main session.

Related issues

• #2604 (broader subagent support)
• #14039 (per-subagent model/provider/profile selection)
• #4432 (auth profile request)

This request is adjacent to those, but narrower:
it is specifically about role/agent presets for the main interactive session, especially with skill scoping.