I agree, also sounds like an unusually well defined role with a clear way of having impact. I would also take this job any day over another job that would bait and switch me into some rewrite death march.

Bring in a spit and polish crew and build towards an evergreen codebase.

But yeah, when you think about -- a sufficiently fecal-encrusted, lost-cause codebase is almost indistinguishable from an actual greenfield opportunity.

Sounds perfectly sensible, and not naive at all.

I'd much rather come into a situation where they were both already aware of, and entirely honest about the current shit-show status of the project -- than a situation where everyone thinks what they're doing is great and bleeding edge but when you actually take a good look at their assets, as it were... not only are they manifestly and visibly unwashed -- but no one seems to notice the stink.