For agents, on top of README.md, which they read first.

• Build and run through the devshell, like everything else here: nix develop -c buck2 build //tools/<name>:<name>.
• Every tool that talks to the window does so over its MCP endpoint and only with tools in the watching router, unless it turns dev mode on for a reason and off again after (hotpatch/patch.sh is the one that does).