Embedded extensions mechanism no longer works

[mcanouil]

Bug description

From https://quarto.org/docs/extensions/formats.html#extension-embedding.

Steps to reproduce

quarto create extension format:html myhtml --no-prompt --no-open
cd myhtml
quarto add mcanouil/quarto-iconify --embed myhtml --no-prompt
echo "{{< iconify simple-icons:quarto >}}" >> template.qmd
quarto render template.qmd --to html

Expected behavior

In the example, Iconify shortcode should be recognised in the template when rendering as it's the case in Quarto 1.3.

Actual behavior

Embedded extensions are no loner available to documents.

Your environment

• macOS

Quarto check output

Quarto 1.3 is the latest known version to work.

[mcanouil]

• Likely related to Gap between errors and documentation in embedding extensions? #10674

[mcanouil]

For future readers: It's actually not a regression/bug but a fix, as embedded extensions are supposed to be used only by the extension embedding them.

This change was unfortunately missed in 1.4 changelog.