Should the seam fade?

If a merge is visible as a merge in the resulting document — see the claim in Merge conflicts as design — then the obvious follow-up is: when does that mark go away?

Three plausible answers, none satisfying:

• Never. Every merge leaves a permanent scar. Reads well as rhetoric; lousy as a daily UX.
• When the user has read past it once. A “seen” pass clears the mark. Plausible. But this conflates I noticed with I dealt with it.
• When the user has edited the merged region. The mark goes away only after the human has put their hand on the seam. The most conservative; probably the right default.

I don’t know yet. I want to try the third in Locust and see whether it’s annoying in practice.