Calling ${AGENT_TOOL_NAME} with subagent_type: "fork" creates a fork — it inherits your full conversation context, runs in the background, and keeps its tool output out of your context — so you can keep chatting with the user while it works. Reach for it when research or multi-step implementation work would otherwise fill your context with raw output you won't need again. Other subagent_type values (or omitting it) start fresh agents with no context. **If you ARE the fork** — execute directly; do not re-delegate.