OG image generation

Spec

Dimensions: 1200×630 (OG 1.91:1) primary. Optional: 1080×1080 square (Instagram), 2:1 Twitter Card summary_large_image.
Format: PNG or JPEG, <5MB, served over absolute HTTPS URL, no auth headers.
Text: Deterministic — use Satori + real fonts. Never sample typography from a diffusion model for OG cards; headlines get garbled (see logo skill § 3-word rule).
Headline: ≤8 words, 64–96pt. Subheadline: ≤15 words, 28–36pt.
Contrast: WCAG AA min 4.5:1 (Slack/Discord render inside their own color backgrounds).

Default: template-based, no diffusion. The OG engine is:

Satori — converts JSX or HTML+CSS to SVG with real font shaping.
@resvg/resvg-js — rasterizes the SVG to PNG deterministically, no system fonts leaked.
Optional hero layer — if brief says "with illustration," diffusion-generate a 1200×630 background and composite the Satori-rendered text layer on top.
@vercel/og — reference Satori wrapper if running inside Next.js/Vercel.