Debugger
A tool that runs your program under your control. It pauses on a line you chose, shows you every variable and the call stack, and moves on one step at a time. Browsers have one built in, and so do most code editors.
Coding agents mostly work by running commands and reading what comes back, so pausing a live program and looking around is awkward for them. For a person it is one of the fastest ways of finding out what is really true, and being able to drive one with the agent off is worth showing.
Say it to your agent
“Give me the exact command to run this test under the debugger, paused at the start, using node --inspect-brk. I will step through parseOrder myself and tell you what I find.”