Filing this on behalf of @mjgallag who writes:

I found this convo while considering logging a feature request to use (and append to) existing shell history. Before devbox I made a decision to go with asdf over dev containers or nix at my company for the primary reason that us devs are persnickety about our shells. I'd like devbox to fade into the background as much as possible and this feels like a rough edge to me.

Previously, we'd implemented a strict separation of devbox shell history and outside shell history in #204. The motivation was that it'll be easier for folks to maintain context for their work within a project by having this separation. That said, as can be seen from the comments in that PR, we had low confidence in whether this was the right choice and wanted to revisit after using it a while. So, thank you @mjgallag for raising the question.