Absolutely this! Tell the right person you want to move into that senior dev position and say you'll work with the senior dev to make that transition. Approac

Absolutely this! Tell the right person you want to move into that senior dev position and say you'll work with the senior dev to make that transition. Approach the senior dev and tell them you'd like to move into their position at some point and want to learn what is needed. Ask for a knowledge transfer (artpar's recommendations are great) and include the non-technical stuff as well, including learning who the key people/groups they need to interact with to do their work. Since it's a small company, I assume the senior dev knows you and hopefully respects your work? If so, ask if they can recommend you for the job?