baseURL for assets referred in frontmatter

[kermanx]

Assets paths in frontmatter won't be resolved by Vite, thus they will be broken once baseURL changes.

However, there is no way to automatically detect whether a string in the frontmatter is a path or not.

We may need a placeholder for base URLs. For example:

---
background: ${BASE_URL}/image.png
# Or ${BASE_URL}image.png because BASE_URL by Vite's definition starts and ends with a slash
---

Ref #2005 (comment)

[jmuchovej]

so, it's possible that ${BASE_URL} would work, but the FAQs on asset handling seems to point to frontmatter will resolve correctly post-build? https://sli.dev/guide/faq#assets-handling

maybe i'm misunderstanding, but i also know that a wrench i threw into the mix as a non-standard kind of asset (.bib and .csl – which are almost exclusively academically used assets).

[lishaduck]

I found that it worked for favicon: /favicon.png, but not for background, which needed background: ./cover.jpg.