Adding "Aptos" font to the Composer font list

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Hi everyone,

I’m trying to set Aptos (Microsoft’s new standard font) as a specific font option when composing emails in Mailspring.

I have already tried creating a custom theme by modifying the .less files (specifically ui-variables.less and composer.less). While I can visually force the font via CSS using font-family: 'Aptos' !important;, I am facing two main issues:

  1. Aptos does not appear in the font dropdown menu within the Composer toolbar.

  2. I want to ensure the font is correctly applied to the outgoing email’s HTML so that recipients (who have the font installed) can see it properly.

I have access to the source code and noticed that the Composer pulls components from mailspring-component-kit. Does anyone know which file contains the toolbar font definitions (the FONT_FAMILIES array) or if there is a cleaner way to register a new font without having to recompile the entire app?

Thanks a lot for your help!