You can ask Shadowheart what she will do once the tadpole is removed and her answer is that she will go her own way and that she has people in Baldur's Gate.

Everyone in Act1 has things to do in Baldur's Gate. Even Auntie Ethel exchanges letters with people in the city. Baldur's Gate is clearly act 2 of the game.

My guess is that the "commit" post Act 1 is in regards to approval. Once the tadpole is dealt with, companions don't necessarily have reasons to stick with you unless they are your friend now (approval at medium+).

Also, I don't think the EA has all of act 1. Larian act concept is narrative based.

DOS1 act 1 is helping Cyseal against Braccus Rex, act 2 is investigating the forest and act 3 was getting to the final boss.
DOS2 act 1 is escape Fort Joy island, act 2 is awakening your powers (Reaper's Cost + Nameless Isle), act 3 is getting to the final boss.
BG3 act 1 is "remove the tadpole"...which can't be completed in the EA.