> - System design at ~whiteboard still feels reasonable / CS basics.

Bingo. Timeless classic for good reason.

Code review also can be good, not in a "can you spot the 17 bugs" way, but rather as a tool for discussing what makes code good, what make a code-review good, what are the tradeoffs in this particular section of code, what tests or other safety checks might you want to add to this particular code, etc.