jupytext --to md:myst *.md should be idempotent

[mwouts]

A comment: jupytext --to md:myst sometimes makes other somewhat disturbing changes that preclude this being a good solution to issue #759. Let me know if I should open a new issue or a couple for each problem. Here are some examples:

Fenced code promoted to code-cells.

This could be bad in an environment where code cells are executed...

# Demo



You should be **very** careful about doing this:

```bash

#rm -rf *   # Commented out just in case!

```

After jupytext --to md:myst *.md this transmutes to

# Demo



You should be **very** careful about doing this:



```{code-cell}

#rm -rf *   # Commented out just in case!

```

which might execute code... also there are whitespace changes (new lines) that break idempotence of the conversion. After several runs of jupytext --to md:myst *.md I get

+++



+++



# Demo



You should be **very** careful about doing this:



```{code-cell}

#rm -rf *   # Commented out just in case!

i.e. added blank notebook cells at the top.

Reference-link replacement.

Here is another example:

# Demo



This is a [reference-link to the issue][].



:::{note}

This note is key... not sure why.

:::



[reference-link to the issue]: <https://github.com/mwouts/jupytext/issues/789>

This gets transmuted to

---

jupytext:

  text_representation:

    extension: .md

    format_name: myst

    format_version: 0.13

    jupytext_version: 1.16.2

---



# Demo



This is a [reference-link to the issue](https://github.com/mwouts/jupytext/issues/789).



This note is key… not sure why.

after which it no longer changes (idempotent). Note that note admonition was removed, and the reference-link was converted to an absolute link.

Originally posted by @mforbes in #789