[App] Add user-confirmed model and reasoning routing for persistent task creation

What variant of Codex are you using?

Codex App (Desktop), with persistent user-visible tasks created through codex_app.create_thread. The local Codex host used for verification is codex-cli 0.146.0.

What feature would you like to see?

Add a first-class, human-in-the-loop model and reasoning routing flow for persistent task creation.

The desired flow is:

1. The coordinating agent evaluates the proposed task.
2. It proposes an exact model and reasoning-effort pair for that task.
3. Codex shows the proposal to the user in a structured confirmation/edit UI.
4. Only after the user approves or edits the pair does Codex create the persistent task.
5. The created task records the proposed, approved, and effective model/reasoning values.

For multiple tasks, the app should support confirming a task-to-model/reasoning mapping as one batch before creation.

Why this is needed

The current create_thread tool accepts model and thinking, but its agent guidance says not to specify a model unless the user explicitly requests a specific model. Otherwise, the fields are omitted and each new task inherits the configured global default.

That is safe, but it prevents an orchestrator from applying task-specific routing unless the user already knows which exact model to request. In practice, a user may want the agent to make the technical recommendation while retaining final control over cost/capability.

In one observed workflow, a coordinator classified several materially different tasks but omitted model and thinking because no exact model had been explicitly requested. All persistent tasks therefore inherited the same global default (gpt-5.6-sol, medium) instead of using the intended per-task routing.

Existing configuration does not cover this surface

The current config schema provides:

• agents.default_subagent_model
• agents.default_subagent_reasoning_effort
• features.multi_agent_v2.expose_spawn_agent_model_overrides

Those settings apply to spawned subagents, not persistent user-visible App tasks created through create_thread.

The managed [models.new_thread] defaults in requirements.toml are static defaults, not a per-task recommendation and approval flow. I could not find a config.toml option for user-confirmed persistent-task routing.

An optional configuration shape could be something like:

[tasks]
model_routing = "confirm" # default | confirm

The exact name is not important; the important behavior is that confirm permits the agent to propose a model/reasoning pair but requires explicit user approval before task creation.

Acceptance criteria

• The agent may propose an exact supported model and reasoning effort for a new persistent task.
• The user can approve or edit both values before creation.
• No persistent task is created until confirmation is received.
• Batch creation presents a clear task-to-model/reasoning mapping.
• The approved values are passed explicitly to create_thread.
• The resulting task exposes the effective model and reasoning effort for auditability.
• If the approved pair is unavailable on the destination host, Codex asks for a new choice instead of silently falling back to the global default.
• The feature remains opt-in and preserves the user's final authority.

Additional information

This is distinct from subagent model routing:

• #31814 covered model overrides for Multi-Agent V2 subagent spawns.
• #32749 exposed model/reasoning overrides for that spawn_agent surface.
• #26767 added global subagent runtime defaults.

It is also narrower than #14923, which requested first-class cross-thread orchestration. Codex App now exposes create_thread; this request concerns the missing user-confirmed model/reasoning selection step when creating those persistent tasks.

Official config schema: https://developers.openai.com/codex/config-schema.json