A deck had exactly one look. The slide vocabulary is structural — bullets,
compare, table, callout, figure — and none of it carries a colour, so "make it
yellow" had nowhere to land but the image prompts, and produced yellow figures
on a blue deck.
A theme is a palette and a typeface in assets/deck-themes.json. render_pptx.py
rebinds INK, MUTED, ACCENT, RULE and PAPER from it in one place, so every slide
builder follows without a line changing in any of them — five themes restyle ten
slide types for free. An unusable theme leaves the default standing, because a
deck in the wrong colours beats a deck that will not render.
The theme rides on the deck, which is already the renderer's spec, so nothing
has to thread it through. It is validated against the same catalogue the
renderer reads: an id the renderer would ignore is never stored, so a deck
cannot claim a look it does not have.
PUT /my-resources/:id/theme re-skins a stored deck — a column write, no model
call, nothing that can reword a slide — and the next download is in the new
colours. Offered in the library only on rows that have a deck; flat markdown has
no palette.
Previews are rendered by the renderer, one representative compare slide per
theme, cached because each costs a pptx render, a Gotenberg round trip and a
rasterise. Drawn rather than mocked up: a hand-made swatch drifts the moment a
palette or a layout changes, and a preview that is not true is worse than none.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Dv6sqaY6Vq3ChZHMem3cnU
