And even if you do use Claude for actual work, there is also immense pedagogical value in writing an agent from scratch. Something really clicks when you actually write the LLM + tool calls loop yourself. I ran a workshop on this at my company and we wrote a basic CLI agent in only 120 lines of Python, with just three tools: list files, read file, and (over)write file. (At that point, the agent becomes capable enough that you can set it to modifying itself and ask it to add more tools!) I think it was an eye-opener for a lot of people to see what the core of these things looks like. There is no magic dust in the agent; it's all in the LLM black box.
I hadn't considered actually rolling my own for day-to-day use, but now maybe I will. Although it's worth noting that Claude Code Hooks do give you the ability to insert your own code into the LLM loop - though not to the point of Eternal Sunshining your context, it's true.