The Timing app for macOS (no affiliation) does essentially that, and then displays in a timeline of sorts. When one really needs to track time spent on tasks/projects, a quick after-the-fact look at the timeline makes it easy to spot blocks of "downright coding", "wondering how to do something", etc.

The UI is great for that as well - identify a block that is made up of several 1-minute back-and-forths between browser and IDE, drag across that, and enter task, for example.