Feature Request: Unified model picker across authenticated providers

Problem

Currently, the model picker only shows models from the active provider, even when multiple providers are already authenticated.

For example, if I'm logged into both Codex (ChatGPT) and Grok, I cannot select a Codex model while Grok is the active provider. I have to switch providers first, then open the model picker again.

I think separating provider and model selection makes sense for CLI arguments and configuration files, where explicit control is useful. However, in an interactive TUI, this feels like exposing an implementation detail that users shouldn't need to think about.

When I open the model picker, my intention is simply to choose which model to use, regardless of its provider.

Proposed solution

Allow the model picker to display models from all authenticated providers, ideally grouped by provider.

Selecting a model from a different provider would automatically switch to the corresponding provider.

This wouldn't require changing the underlying provider architecture or removing explicit provider selection. Existing restrictions on switching providers during active operations could remain in place.

Why this matters

One of fx's appealing features is its ability to use multiple AI subscriptions through a single interface.

A unified model picker would make that experience much more seamless, especially for users who frequently switch between models from different providers.

The provider is still an important implementation and configuration detail, but I don't think it needs to be a prerequisite for selecting a model in the TUI.