A deck in demolab is a talk, not a writeup. It lives at writings/<id>.slide.typ and is built with Touying into a standalone PDF. The .slide.typ filename is the marker: the build compiles the deck on its own, links it from the site, and deliberately excludes it from the HTML pages and the book. Touying is paged-only and does not survive HTML export, so a deck stays a PDF and nothing else.
One structural difference from a prose entry: a deck declares #let meta so the site can list and link it, but it never declares a #let body. Its figures come from the same committed run outputs the writeups read, out of artifacts/data/, never from ad-hoc images.
A slide is a fixed rectangle: 842 by 474 points at 16:9. Once the title header and footer margins take their share, you have roughly 350 points of usable height on a titled slide. That number is the budget you lay everything out against. Size images in absolute points, not percentages: a percentage resolves against whatever region encloses it, which inside a grid cell is rarely the whole slide, so percent-sized figures come out unpredictably small and can overflow. Give each figure row a height that suits its shape, sum the rows, gutters, and captions, and confirm the total stays under budget. If a slide is mostly whitespace the figures are too small; if things do not fit, split the slide rather than shrinking text below readable sizes.
Overflow is silent. Oversized content does not clip or raise an error; Touying quietly spills it onto an extra page, and the deck grows without warning. So after every layout change, count the pages and compare against the number of slides you meant to have. Render the deck to images and count them, rather than trusting cached metadata from Finder or Spotlight, which goes stale. Then eyeball the dense slides at higher resolution to catch clipped captions or terms swallowed into a subscript.
You do not re-derive a layout from scratch. Every layout is a named, tested block in the gallery deck, and the guide carries an index of names paired with when to use each one: bullets, two-column comparisons, code panels, equation-with-terms, figure grids, big-number statements, section dividers, and more. You find the name, copy that block out of the gallery, and swap in your own content. The gallery holds the single page-count-checked copy of each layout, and a test keeps the index and the gallery in sync, so an entry can never point at a missing block.
You can also just type SLIDES in capitals and the coding agent will walk you through all of this interactively.
The full reference lives in SLIDES.md.