You’re painting it too binary. Once you’ve seen a few dozen codebases you get pretty good at recognizing the patterns. A senior engineer could/should absolutely

You’re painting it too binary. Once you’ve seen a few dozen codebases you get pretty good at recognizing the patterns. A senior engineer could/should absolutely be able to familiarize themselves with the general structure of a new codebase in a matter of minutes/hours to the point that they could reasonably start directing a more junior engineer within it. It’s not “go to this file and do X, Y, and Z starting at line 105”, but more like “Ok so it’s likely that the source of this data is coming from a feed, track down the feed consumer by grepping for [upstreamservice] in the feeds directory, and from there we can get a look at what we’re doing with the incoming feed data”