I mean I suppose you can continuously add "critical feedback" to the system prompt to have some measure of impact on future decision-making, but at some point you're going to run out of space and ultimately I do not find this works with the same level of reliability as giving a live person feedback.

Perhaps an unstated and important takeaway here is that junior developers should not be permitted to use an LLMs for the same reason they should not hire people: they have not demonstrated enough skill mastery and judgement to be trusted with the decision to outsource their labor. Delegating to a vendor is a decision made by high-level stakeholders, with the ability to monitor the vendor performance, and replace the vendor with alternatives if that performance is unsatisfactory. Allowing junior developers to use LLM is allowing them to delegate responsibility without any visibility or ability to set boundaries on what can be delegated. Also important: you cannot delegate personal growth, and by permitting junior engineers to use an LLM that is what you are trying to do.