[Coda]

Oh wow. Huh.

This analyzer that I'm working on isn't all that smart. It implements exactly the same technique I use when I start a puzzle -- it fills in all of the squares that have to be filled in no matter how you organize the hints for that row/column, then it fills in all of the squares where the edge hints make it unambiguous how far inward you have to go, then it puts in X's at the endpoints of fully-satisfied hints, then it puts in X's on the edges if the hint can't reach it given the rest of the information.

And yet even as simple as it is, I thought I had found a bug in it. It X'ed a few squares that had me scratching my head -- why would it mark THOSE?

A few minutes of debugging later... Oh. That's NOT a bug. That's completely right, and I wouldn't have noticed.