Add a 'Render diagrams and formulas natively' section to the wiki skill:
prefer native Mermaid for diagrams and KaTeX ($...$) for formulas over ASCII
art / unicode-in-code, as the default (but not for the sake of it). Records the
mechanics learned in practice — Mermaid label/colour discipline and real-render
validation; KaTeX as a LaTeX-math subset, dollar-only delimiters, the table
pipe/percent escapes, and the closing-$-glued-to-slash boundary trap — plus the
two-gate validation discipline (parser gate + Gitea render-parity, table
integrity, adversarial semantic-equivalence), since valid != correct != rendered.
Also a checklist item and a description clause.
Brummel
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