Qwen barely needs any of Opencode's prompt, in my experience; I think I cut it down to about three general lines I found by googling. Mainly you need only a pre-amble to make sure that the plan mode, plan switch and build mode prompt fragments make sense.
Gemma 4 also needs almost nothing at all, which is fascinating, considering it is not a coding-specialist model. It just seems to be who you need it to be when you ask.