Evaluate Sätteri (Rust markdown/MDX processor) as an Astro processor swap

[ace139]

Context

Evaluate whether to swap Astro's markdown/MDX engine from the default unified() (remark/rehype) to Sätteri — "A Markdown pipeline forged in Rust for the JavaScript world." It's a Rust-based Markdown/MDX processor (not a site generator) exposing HAST/MDAST ASTs and a typed plugin API via napi-rs, with a WASM build.

Findings (as of 2026-06-29)

• It's a supported swap. Astro 6.4.4 exposes a pluggable markdown.processor option, and there's an official @astrojs/markdown-satteri package. Astro core even has satteri-specific handling baked in. Adoption would be: markdown: { processor: satteri({ mdastPlugins: [...] }) }.
• Maturity risk. @astrojs/markdown-satteri is v0.3.2 (published ~2026-06-23, pre-1.0, alpha/beta history).
• Scope. Satteri only touches the content-rendering path (src/content/** → HTML). It does NOT replace scripts/generate-markdown.js, which converts HTML → Markdown (opposite direction) for the Accept: text/markdown agent feature.
• Performance win is negligible at current scale (~10 posts); build-time markdown parsing is not a bottleneck.
• Compatibility risk = the deciding factor. rehype-mermaid is a HAST/rehype plugin; Satteri uses its own mdastPlugins/native plugin API, so whether it runs unchanged is unverified. Dual-theme Shiki likely survives (Astro applies highlighting outside the processor) but needs a real build to confirm.

Decision so far

Stayed on unified() and migrated off the deprecated remarkPlugins/rehypePlugins config shape onto markdown.processor: unified({ rehypePlugins: [rehypeMermaid] }). The processor slot is now the clean seam to A/B Satteri later.

To revisit later

• Re-check @astrojs/markdown-satteri maturity once it hits 1.0 / stabilizes.
• On a branch, swap unified(...) → satteri(...) and run bun run build; verify rehype-mermaid and dual-theme Shiki output.
• Only adopt if the build is clean AND there's an actual reason (e.g. build-time pain at larger content scale).

Links: https://satteri.bruits.org/ · https://github.com/bruits/satteri · @astrojs/markdown-satteri on npm