Render Markdown or LaTeX artifacts with pandoc through the shell. feynman setup preview checks for pandoc, and feynman doctor reports whether it is available.
pandoc outputs/<slug>.md -s -o outputs/<slug>.html # HTML
pandoc outputs/<slug>.md -o outputs/<slug>.pdf # PDF (needs a LaTeX engine)
open outputs/<slug>.html # macOS; xdg-open on Linux
Rendered HTML and PDF files are previews; the Markdown artifact stays canonical. If pandoc or a LaTeX engine is missing, say so and leave the Markdown artifact as the deliverable.