This is a VSCode extension that monitors the main process of an active DebugSession for spawned child processes. Once a child process is identified, an attempt will be made to attach a new DebugSession to that child process. If source code is available in the current workspace, the attach will succeed and the child process can be stepped through.
This extension is really useful for applications that spawn child processes. Take the following C# code for example:
Normally, in order to debug the node process you would need to sleep the current thread and manually attach the debugger. Harpoon will discreetly check for the system for child processes every second.
Using the VSCode Debug control overlay, you can move between active debug sessions by selecting from the dropdown on the right side. This also applied to other VSCode tool windows like Output and Debug Console.