Subject: Re: Partial IRA to Roth Rollover
Me: “Well, the idea is that the pretax part plus all earnings is pushed to the 401k, which isn’t actually considered a rollover (I think), leaving exactly the after tax part.”

Correction: it is a “rollover”, but it’s not subject to the one per year rule since it is going to a qualified plan, in this case a solo 401k.