[FEATURE]: ability to revert/fork from the ai message, not only from the user's

Feature hasn't been suggested before.

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Describe the enhancement you want to request

PROBLEM: Currently, we can only respond to or create a fork from the user's message, which is suboptimal in many ways. We cannot revert to the middle of the AI model's actions or some of the model's thoughts, to correct/address them right away.

E.g., it's common for me to only have one message at the start of the session, which effectively prevents me from using these options. Sometimes, when I realise that the AI model is behaving incorrectly, I can’t do anything about it except start the session again from the very beginning.

If OpenCode provided the ability to revert or fork from one of the model's messages or tool calls, we could choose the exact moment when the model started to malfunction, which would increase the efficiency of the whole workflow tremendously.

Is it possible to support that?