I watched a video demo of a new Visual Studio Code plugin for Autodesk Fusion 360 "postprocessor" plugins, which are evidently written in JS. These emit G-Code — I think they might take G-Code as input, but I'm not sure. The video demo showed a feature similar to Bret Victor's famous tree-landscape-drawing demo, in which by clicking on a piece of G-Code in the output, you would immediately jump to the line of source code that emitted it.
This is a super cool feature, and I realized that I really want this for debugging printfs in general: I want to be able to click on a debug log message and get a stack trace of the program as it was at the moment the log message was emitted. Perl's Carp module has provided such a facility in a purely textual form for a long time, and Purify and Valgrind have provided it for memory allocation, but I want to be able to do it for any output, especially debugging output.
Moreover, I especially want to be able to do this for immediate-mode GUIs; I want to be able to jump from a GUI control on the screen into the code that painted it, and see the stack trace as it was at the moment that control was painted. This is actually maybe easier to provide than the purely textual version of this feature, because if the feature is still there on the screen when I click on it, and the program is still running, that stack is actually running at the moment that my click is delivered.
Delivering this functionality for screenshots and recorded sessions would be harder.