Isolating work in its own context window: delegate a self-contained subtask to a subagent with a fresh window and a small toolset, let it burn what it burns, accept back a distilled result. Two doors, strictly kept: what may enter is the brief you wrote, and what may come back out is conclusions—treated as evidence to weigh, never instructions to obey. Also the wall between untrusted content and consequential action (Chapters 7, 9, and 17).