I'd say both, personally. On the app Sync (for a different platform), I was able to swipe away the current context to return to the previous one, going one layer at a time back to the homepage.

So I'd say ideally (and this is likely too much work to adjust), clicking a post should layer it over the current context. Clicking a close button or swiping with touch or cursor removes that contextual overlay. Ctrl/cmd click still opens a new tab instead, as does middle click. This could be a configuration setting that needs enabled, but applies at mobile sizes. Keep all normal href data (some services implement that in a way that prevents middle click/etc. from opening the new context in a new tab/window).

Maybe too "appy" for a website, but it was quite a nice interface for a native Android app.

Thanks for hosting this instance, BTW