0002. The UI font is a system option, apart from the colors

The UI font is one system option, next to its package and apart from the colors, read everywhere.

• Status: accepted
• Date: 29/07/2026; it was rule 10 until 30/09/2026

Context

Seven consumers named the UI font as a literal. The font is also read by fontconfig, which is system level, while most of the consumers are home-manager modules.

Decision

my.fonts.ui is declared in modules/nixos/desktop/fonts.nix, next to the font package, and not next to the palette. A home-side consumer reads it through osConfig.my.fonts.ui.

Consequences

• Changing the font is one line plus the package.
• It had to be a SYSTEM option: a system module cannot read a home-manager option, and fontconfig needs the name too (rule 11's "the lowest level that needs it").
• Colors and font are two separate choices, so a theme change never moves the font.