[FEATURE]: Introduce ordered list for model options #13977

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

There are requests open that go in this direction, but not quite the same. The issue is the following:

Imagine you have clearly defined agents and subagents, but the projects you work each have different providers you're allowed to use. This means that in theory, you'd have to duplicate the definitions for each, as the setup only allows the definition of one model:

{
  "agent": {
    "plan": {
      "model": "anthropic/claude-haiku-4-20250514"
    }
  }
}

Now there are two possible options to manage this:

1. Introduce grouping of models in openCode.

The idea is simple: We create "tiers" of models and assign them to each model. I.e. haiku could be limited, sonnet would get efficient and opus would get complete (as example).
This would then allow the users to define agents as follows:

{
  "agent": {
    "plan": {
      "model": {
         "type_filter": "efficient"
      }
    }
  }
}

This way it would automatically select the applicable one.

2. Allow definition of model list in agent definition

Self explanatory, here is an example:

{
  "agent": {
    "plan": {
      "models": [
         "anthropic/claude-sonnet-4-5",
         "openai/gpt-5"
      ]
    }
  }
}

Considering we can turn off providers per project using the configuration, this would allow user level definitions that can be carried around projects. If first one isn't available, try second one.