"Color selection" off-by-one regression: it colors 1 cell past the end

[jazzdelightsme]

Windows Terminal version

1.23.10732.0

Windows build number

10.0.26388.1001

Other Software

No response

Steps to reproduce

I use the "Color Selection" feature a lot, and often the "all matches" variant, which lets you select some text, and then change the fg/bg color for all occurrences of the selected text.

Recently it started coloring one cell past the end of the selection. In the screenshot below, I selected "abcd", but the colorization applies to "abcde" (as well as "abcdeX", demonstrating that the search is not similarly afected):

Expected Behavior

Just the "abcd" should have been colorized.

Actual Behavior

Colorization included one character past the end.

[jazzdelightsme]

As we all know, the two hardest things in computer science are naming things, cache invalidation, and off-by-one errors. :D

[DHowett]

Alas, another victim of #18106