Thanks for giving B29 a try, wburd, and for the detailed feedback! It's helpful to know that it started in about 20 seconds on desktop Chrome without loading failures.
A short merge hint sounds useful, especially since the other actions already have prompts.
The Stage 4 healer fight is the main concern in your report. With the party you described, being stuck attacking the front slimes without a clear way to deal with the healer sounds frustrating. The exact party composition is useful for checking the encounter balance and how targeting is explained.
Do you remember whether your two Mages were in the front or back slots when you got stuck? That would help reproduce the situation.
Thanks again—I'm glad you'd be interested in playing more! You're welcome to share the link to your playtest too.