additional-packages vs header-includes

[amael-ls]

It seems that using additional-packages does not work with quarto and html output, but header-includes does. Here are two MWE, where the first one fails and the second one succeed to reproduce the expected results (a node a and a node b 3 cm lower):

Fails

---
title: "A tikz diagram extension test"
filters:
  - diagram
pdf-engine: lualatex
diagram:
  engine:
    tikz:
      execpath: lualatex
      additional-packages: |
        \usetikzlibrary{positioning}
---

## Test section
```tikz
\begin{tikzpicture}
	\node (a) at (0, 0) {a};
	\node[below = 3cm of a] (b) {b};
	\draw (a) -- (b);
\end{tikzpicture}
```

Works

---
title: "A tikz diagram extension test"
filters:
  - diagram
pdf-engine: lualatex
diagram:
  engine:
    tikz:
      execpath: lualatex
      header-includes:
        - '\usetikzlibrary{positioning}'
---

## Test section
```tikz
\begin{tikzpicture}
	\node (a) at (0, 0) {a};
	\node[below = 3cm of a] (b) {b};
	\draw (a) -- (b);
\end{tikzpicture}
```

quarto check

❯ quarto check
Quarto 1.6.41
[✓] Checking environment information...
      Quarto cache location: /home/MY_NAME/.cache/quarto
[✓] Checking versions of quarto binary dependencies...
      Pandoc version 3.4.0: OK
      Dart Sass version 1.70.0: OK
      Deno version 1.46.3: OK
      Typst version 0.11.0: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
      Version: 1.6.41
      Path: /opt/quarto/bin

[✓] Checking tools....................OK
      Chromium: 869685
      TinyTeX: (not installed)

[✓] Checking LaTeX....................OK
      Using: Installation From Path
      Path: /usr/local/texlive/2024/bin/x86_64-linux
      Version: 2024

[✓] Checking basic markdown render....OK

[✓] Checking Python 3 installation....OK
      Version: 3.12.3
      Path: /usr/bin/python3
      Jupyter: (None)

      Jupyter is not available in this Python installation.
      Install with python3 -m pip install jupyter

[✓] Checking R installation...........OK
      Version: 4.4.2
      Path: /usr/lib/R
      LibPaths:
        - /home/MY_NAME/R/x86_64-pc-linux-gnu-library/4.4
        - /usr/local/lib/R/site-library
        - /usr/lib/R/site-library
        - /usr/lib/R/library
      knitr: 1.49
      rmarkdown: 2.29

[✓] Checking Knitr engine render......OK

[tarleb]

Thanks for the report. The README contains the sentence "The
options differ only in how string values are handled, with bare
strings in header-includes being escaped and those in
additional-packages being treated as TeX code." Maybe this could be improved to make the behavior a bit clearer.

Suggestions would be most welcome.