Unfortunately many subscriptions require you use their harness. In that case, I highly recommend using Termic (https://github.com/simion/termic/).

It's an incredibly useful GUI that lets you use the provider's harness, but adds extra productivity features. You can use OpenCode, Pi, Claude, Codex, whatever you want. The TUI runs in a window, but you can also pull up terminals, open tabs, keep projects, workspaces, show file diffs, give feedback on lines of code, review PRs, and way, way more. The number of features is impressive.

The devs are very quickly adding features, yet the app remains stable. And they fix bugs super fast! They fixed like three bugs and implemented two feature requests of mine within a week of asking. Best of all the whole thing is FOSS and they're not trying to make money off you. Absolutely awesome maintainers.