I have a small tool to manage agents, and one thing it does is let you select an --agent [codex|opencode|etc] and a --model. Valid --model values are specific to the agent though, and some agents like opencode support a huge amount of models.

When I added tab completion for --model that accounts for what --agent is set to, it made it 100x easier to use and I stopped relying on the defaults so much.

It's such a small thing but makes a big difference for discoverability.