chore: use rumdl for Markdown formatting (#9)

Move Markdown formatting from prettier to rumdl (mystmd flavor for
content/, standard for the Marp slides/). prettier stays for the
non-Markdown files (CSS, JSON, YAML) via an `\.md$` exclude.

rumdl fmt's directive-aware fixes (MD031) add blank lines around MyST
directives; MD013/MD033/MD026/MD076 are disabled as they don't fit
prose/slide content.

Assisted-by: ClaudeCode:claude-opus-4.8

Author: henryiii

.pre-commit-config.yaml

@@ -33,10 +33,16 @@ repos:
     hooks:
       - id: nbstripout
 
+  - repo: https://github.com/rvben/rumdl-pre-commit
+    rev: "5c0245ee573b1dea03e8cdc5bd41bd449ea8962a" # frozen: v0.2.27
+    hooks:
+      - id: rumdl-fmt
+
   - repo: https://github.com/rbubley/mirrors-prettier
     rev: "515f543f5718ebfd6ce22e16708bb32c68ff96e1" # frozen: v3.8.3
     hooks:
       - id: prettier
+        exclude: '\.md$' # Markdown is handled by rumdl
 
   - repo: https://github.com/codespell-project/codespell
     rev: "2ccb47ff45ad361a21071a7eedda4c37e6ae8c5a" # frozen: v2.4.2

.rumdl.toml

@@ -0,0 +1,12 @@
+[global]
+# This is prose-heavy content, not source-tree Markdown.
+disable = [
+    "MD013", # Line length — prose and code samples are not hard-wrapped
+    "MD033", # Inline HTML — Marp slides use <div class="columns"> etc.
+    "MD026", # Trailing punctuation in headings — slide headings intentionally end in ":"
+    "MD076", # Blank line between list items — false-positives inside mixed-indent MyST :::{card}
+]
+
+# content/ is MyST (directives, roles); slides/ are Marp (standard Markdown + HTML).
+[per-file-flavor]
+"content/**/*.md" = "myst"

AGENTS.md

@@ -14,7 +14,7 @@ bun run build         # build book + slides into _build/html/ (build-book then b
 bun run build-book    # myst build --html
 bun run build-slides  # marp slides/ -> _build/html/slides/
 bun run clean         # rm -rf _build
-prek -a --quiet       # lint/format everything (ruff-format, blacken-docs, prettier, codespell, etc.)
+prek -a --quiet       # lint/format everything (ruff-format, blacken-docs, rumdl, prettier, codespell, etc.)
 ```
 
 ## Structure

README.md

@@ -2,4 +2,4 @@
 
 This workshop is a work in progress. Check back soon!
 
-See https://scikit-build.org/events/simple-py/ for info on the workshop!
+See <https://scikit-build.org/events/simple-py/> for info on the workshop!

content/basic-packaging/01_setup.md

@@ -65,13 +65,15 @@ When Python runs, it checks to see if there's a `pyvenv.cfg` above it. If there
 it is in a virtual environment (venv) and reads site-packages from there. There are two ways to use it:
 
 ::::{tab-set}
+
 :::{tab-item} Direct usage
 
 ```bash
 .venv/bin/python ...
 ```
 
 :::
+
 :::{tab-item} Activation
 
 ```bash
@@ -81,6 +83,7 @@ deactivate
 ```
 
 :::
+
 ::::
 
 > [!WARNING]
@@ -95,7 +98,9 @@ The `.` at the start (most shells support `source` as well) allows the activatio
 To create one of these, you have several options:
 
 :::::{card} Create a virtual environment
+
 ::::{tab-set}
+
 :::{tab-item} venv
 
 ```bash
@@ -105,6 +110,7 @@ python3 -m venv .venv
 This is the slowest, but it's built in![^1]
 
 :::
+
 :::{tab-item} virtualenv
 
 ```bash
@@ -114,6 +120,7 @@ virtualenv .venv
 This is faster than `venv`, has better default installs inside, but does require installation.
 
 :::
+
 :::{tab-item} uv
 
 ```bash
@@ -123,7 +130,9 @@ uv venv
 This is really fast, though it's completely empty (no pip). And it defaults to `.venv`. Also requires installation (a single Rust binary or pip install).
 
 :::
+
 ::::
+
 :::::
 
 We will be using `uv`, which can do a lot of this for us.
@@ -137,7 +146,9 @@ Now that you know how to make virtual environments, how should you install stuff
 But a virtual environment is meant to be expendable. You should be able to delete it and recreate it any time. So instead of manually installing, you want to list packages in some format:
 
 :::::{grid} 1 1 2 2
+
 ::::{grid-item}
+
 :::{card} Project (app)
 These are for making a virtual env. They don't affect libraries.
 
@@ -148,8 +159,11 @@ These are for making a virtual env. They don't affect libraries.
 - **Lock file**: Versions are pinned exactly
 - **dependency-groups**: Multiple collections of packages
   :::
+
   ::::
+
   ::::{grid-item}
+
   :::{card} Package (library)
   These are for libraries.
 
@@ -164,7 +178,9 @@ Most libraries also have developer environments, which follows the "Project
 > for these too; this is due to it pre-dating `dependency-groups`.
 
 :::
+
 ::::
+
 :::::
 
 Locked dependencies means that every dependency is fully specified, ideally
@@ -296,20 +312,23 @@ if __name__ == "__main__":
 When you run it:
 
 ::::{tab-set}
+
 :::{tab-item} uv
 
 ```bash
 uv run single.py
 ```
 
 :::
+
 :::{tab-item} pipx
 
 ```bash
 pipx run single.py
 ```
 
 :::
+
 ::::
 
 The dependencies will be downloaded into a temporary venv.

slides/1_01_setup.md

@@ -74,7 +74,7 @@ System or user installs sound nice, but:
 
 ## Virtual environment structure
 
-```
+```text
 .venv
 ├── .gitignore
 ├── CACHEDIR.TAG