I've gotten quite a bit of utility out of my current setup[0]:

Some explicit things I found helpful: Have the agent address you as something specific! This way you know if the agent is paying attention to your detailed instructions.

Rationality, as in the stuff practiced on early Less Wrong, gives a great language for constraining the agent, and since it's read The Sequences and everything else you can include pointers and the more you do the more it will nudge it into that mode of thought.

The explicit "This is what I'm doing, this is what I expect" pattern has been hugely useful for both me monitoring it/coming back to see what it did, and it itself. It makes it more likely to recover when it goes down a bad path.

The system reminder this article mentions is definitely there but I have not noticed it messing much with adherence. I wish there were some sort of power user mode to turn it off though!

Also, this is probably too long! But I have been experimenting and iterating for a while, and this is what is working best currently. Not that I've been able to hold any other part constant -- Opus 4.5 really is remarkable.

[0]: https://gist.github.com/ctoth/d8e629209ff1d9748185b9830fa4e7...