I can reproduce this issue on Typst v0.11.x, but cannot reproduce it on main branch. Using git bisect, I found #4212 fixed this issue.

I'm still able to reproduce the issue on main, only it happens with the left parenthesis instead of the right one:

#{
  show "(": it => context it
  $ (1 / 2) $
}
#{
  show ")": it => context it
  $ (1 / 2) $
}
#{
  show "(": it => context it
  show ")": it => context it
  $ (1 / 2) $
}

(sorry for the low quality, I think the problem is visible anyway).

For comparison, I get the following result in 0.11.1:

Note that using context without a show rule breaks both parentheses (on both main and 0.11.1):

$ #context "("1 / 2#context ")" $

Debugging (on main e90c309) indicates that in the cases where ( is replaced with context("("), there is an extra MathFragment::Frame at the start of the lr element’s body containing a tag for the context.

This issue is similar to #3727 in that it’s related to ignorant or invisible elements affecting math layout. It still occurs on #4348, but it should provide the machinery to implement a similar fix for lr elems.