In other words, permanent instructions and context well presented in *.md, planning and review before execution, agentic loops with feedback, and a good model.

You can do this with any agentic harness, just plain prompting and "LLM management skills". I don't have Claude Code at work, but all this applies to Codex and GH Copilot agents as well.

And agreed, Opus 4.5 is next level.