> So the thing solving them will sometimes have to be able to reason quite well across large code bases
The codebase only describes what the software can do currently, never the why. And you can't reason without both. And the why is the primary vector of changes which may completely redefines the what. And even the what have many possible interpretations. The code is only one specific how. Going from the why, to the what, to a specific how is the core tenet of programming. Then you add concerns like performance, reliability, maintainability, security...
Once you have a mature codebase, outside of refactoring and new features, you mostly have to edit a few lines for each task. Finding the lines to work one requires careful investigation and you need to carefully test after that to ensure that no other operations have been affected. We already have good deterministic tools to help with that.
The codebase only describes what the software can do currently, never the why. And you can't reason without both. And the why is the primary vector of changes which may completely redefines the what. And even the what have many possible interpretations. The code is only one specific how. Going from the why, to the what, to a specific how is the core tenet of programming. Then you add concerns like performance, reliability, maintainability, security...
Once you have a mature codebase, outside of refactoring and new features, you mostly have to edit a few lines for each task. Finding the lines to work one requires careful investigation and you need to carefully test after that to ensure that no other operations have been affected. We already have good deterministic tools to help with that.