Font Library: Uploaded custom font not included in exported Block Theme

[bfintal]

Description

The custom font I've uploaded isn't included when exporting the Block Theme. The custom font is still selected in style typography settings though.

Step-by-step reproduction instructions

1. Open nightly in Playground: https://playground.wordpress.net/?wp=nightly&plugin=gutenberg
2. Go to Site Editor and upload a custom font
3. Use the custom font for headings
4. Export the theme
5. Open a fresh site and install and activate the exported theme
6. See that the uploaded font is not there

Screenshots, screen recording, code snippet

If you check the exported theme.json, the font file is not found in there - it's source is referenced from the original. For example, I've uploaded a copy of DM Sans:

{
	"fontFace": [
		{
			"fontFamily": "DM Sans",
			"fontStyle": "normal",
			"fontWeight": "100 1000",
			"src": "https://playground.wordpress.net/scope:0.0731139000825751/wp-content/fonts/dm-sans_normal_100-1000.ttf"
		}
	],
	"fontFamily": "'DM Sans'",
	"name": "DM Sans",
	"slug": "dm-sans"
}

Environment info

https://playground.wordpress.net/?wp=nightly&plugin=gutenberg

• WordPress 6.5-alpha-57272
• Gutenberg 17.4.1

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes

[mikachan]

Thanks for reporting, @bfintal! We're discussing how best to handle font exports when a theme is exported here: #54226. I'll close this issue as a duplicate, but please feel free to join in the discussion there.