A senior's design will make one part of the code painful to change later. Do I flag it?

A senior on my team laid out an approach for a feature we're starting, and one piece of it nags at me — I'm fairly sure it'll lock in a decision that gets expensive to unwind once we build on top of it. Not a bug. Just a shape that'll hurt in six months.

Here's my problem: I'm eight months in. When something "feels wrong" from someone with my experience, the base rate is that I just haven't seen why it's right yet. So I can't tell if I'm spotting a real trap or pattern-matching on nothing.

I don't want to be the junior who thinks they know better after eight months. I also don't want to sit on a concern that proves real and then admit I saw it coming and said nothing. If you've been the junior in this spot, how did you raise it — and how did you make peace with being wrong the times you were?