Respect user set default_mode and improve agent management

[guillaumeboehm]

This PR aims to improve some of the agent switching and default behaviors.

I encountered an issue because my default agents are disabled in my opencode config, and the plugin always added them to the available agents and ignored the default_mode set by the user.

Here's an overview of what this PR changes:

• The default_mode option was not being respected when setting the
  state current_mode. The current_mode is now set when first opening the
  opencode window.
• The mode switching is now wrapped in a "switch_to_mode" function to
  ensure the mode exists in the available agents for more control.
• The build and plan agents were added to the available agents even if
  explicitly disabled in the opencode config -> leading to a hang when
  sending messages to opencode. They are now prepended if they are not
  disabled.
• The agent list was always randomly returned, it is now sorted before
  using it.

[guillaumeboehm]

Ah looks like the tests are broken... I obviously ignored them as hard as I could 🤣 I'll figure out how to run them and check what's wrong.

[sudo-tee]

Take your time. Otherwise it looks like a good feature

[guillaumeboehm]

Take your time. Otherwise it looks like a good feature

Yeah I figured out what's the issue but I'm struggling to fix it xD When the renderer test is being run, it's using the user opencode config instead of a mock config, and the expected 'BUILD' agent in the topbar is not here in my case.
So I'm trying to make the renderer tests use a mock config, but it's not going smooth xD

[sudo-tee]

@guillaumeboehm

I've had a look at it and I think it's just that the mode is never set for the renderer_spec as it never calls api.open that calls your ensure_mode. Where before the mode was set directly in the state.

I pushed a fix for the tests to your branch.

I also removed a render_output in the ensure_mode, as it's unecessary since it's done in the open method.

Can you just do a last test to ensure everthing is fine, and after that I can merge this

[guillaumeboehm]

Thanks! It works great now I think. I also added a little test in the config_file tests to test the disabled agents case.