その回答（■から）
Instead of saying, "Did you come here yesterday, too?", can you say, (1) "Did you, too?" and (2) "So did you?"?

■Yes

Are (1) and (2) both OK? Yes If (2) is not OK, could you tell me why?

■But note this.

Using 'so' like this implies that the speaker thinks you had some reason to come.

Jim;: My mother asked me to come.

Tom: So did you?

How about this situation?: 以下略

■Yes, if you think that Grace's beauty makes it likely that Emily also is beautiful.
引用終わり

この"that the speaker thinks you had some reason to come."の"you"は
"the speaker"（この文ではTom")を指すのかな？
トムも来なくちゃいけない理由があった場合に、Jimに、（俺も来なくちゃいけなかったけど）君も来たの？と訪ねてる場合かな