Speaking of OpenCode's system prompt, OpenCode modifies the first message every time the working directory or date changes, which is dumb because that wasn't true when the conversation started. Transcripts are supposed to be historical records... Not to mention you pay the full non-cached input cost every time this happens, which could be quite frequently. Use a better agent like Pi.

I don't think that is true. It would be extremely noticeable (zero caching) and I am not noticing it.