Doesn’t handle PUA characters well

[nisbet-hubbard]

Checklist

• Using latest version on the App Store
• Read the docs
• Searched for existing GitHub issues

Configuration

18.4.2 build 1051, iPadOS 26.1

Describe the bug

In iterms2, Unicode Private Use Area characters are displayed in whatever font in the fallback order on the computer has a glyph at the particular code point. On blink, they show up as a replacement character or nothing.

	iTerms2	Blink case 1	Blink case 2
nvim	correct glyph	replacement character	nothing
git diff --staged	correct glyph	code like <U+F4DA9>	nothing

Case 2 is problematic because one can’t even know that a character is there, and it distorts the positioning of all the characters to the right such that one can’t insert anything at correct position based on the visual feedback.

And it’s unclear which PUA code points fall into case 1 and which case 2.

[carloscabanero]

Linking this to #1980