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A 19-minute Claude Code walkthrough names the nine features most devs never touch, and gives the context-window reason sub-agents matter
Tech With Tim published this on 2026-09-07 covering custom sub-agents, skills, hooks, MCP servers, parallel sessions via git worktrees and headless mode, each with a demo. The sub-agent section is the useful part and matches how the feature actually works: agent specs are markdown files under a nested agents folder with name, description, allowed tools and an optional model per agent (which he flags as the cost lever when running many), `/context` confirms they registered, and only the sub-agent's response returns to the main thread. His stated rule is to create one only when you want work delegated out of the main thread with specific tool or read-only constraints, not by default.
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