Codex Desktop: add a bulk action to switch existing tasks to a new model

What variant of Codex are you using?

Codex Desktop on macOS.

What feature would you like to see?

Add a supported bulk action for changing the model (and optionally reasoning effort) of existing Codex tasks/conversations.

For example, under Settings > Model:

• Set as default for new tasks
• Apply to existing tasks...

The bulk action should offer safe scopes:

• non-archived tasks only (default)
• tasks in the current project
• all projects
• optionally include archived tasks
• only replace a selected source model, such as GPT-5.5, so intentionally pinned custom/older models are not overwritten
• optionally migrate reasoning effort separately

It should show the number of affected tasks and require confirmation.

Why this is needed

Changing the global default in ~/.codex/config.toml, for example:

model = "gpt-5.6-sol"
model_reasoning_effort = "xhigh"

sets the desired default, but Codex Desktop also persists model selection per thread. Existing tasks can remain recorded on the older model and otherwise have to be opened and changed individually with the model picker.

On one real local profile after changing the global default to GPT-5.6 Sol, the supported state index still reported:

174 non-archived tasks on gpt-5.5
33 archived tasks on gpt-5.5

With hundreds of existing tasks, changing them one by one is impractical. Directly editing ~/.codex/state_5.sqlite is unsupported and risks conflicting with app reconciliation.

Expected behavior

A user should be able to explicitly migrate selected existing tasks from one model to another in one supported operation. Afterward:

• the task's picker shows the target model
• resuming the task uses the target model
• unrelated/custom-provider tasks remain unchanged
• thread history and context are preserved

This should be an explicit user action, not an automatic overwrite of every existing task whenever the default changes.

Related issue

• #32061 requests that normal CLI resume preserve a task's previously selected model. This request is complementary, not a duplicate: preserve per-task settings by default, while providing an explicit bulk migration action when a user chooses to upgrade many tasks.

Environment

• Codex Desktop: 26.715.31925 (build 5551)
• Bundled Codex CLI: 0.145.0-alpha.18
• macOS 26.5.1 (25F80)