docs: markdown panes support KaTeX ($…$ / $$…$$) but the type table doesn't say so — authors emit code-fences instead

[ivanmkc]

Observed: When authoring a markdown / panes view, equations written as code-fences (or Unicode approximations) don't typeset — because the author had no signal that real math is supported. (Context: this surfaced while an agent built a math-heavy explainer via termchart push; it defaulted to a monospace code-fence for the equations.)

Root cause: The renderer does support LaTeX math. packages/viewer/src/client/renderers/markdown.ts enables marked-katex-extension so inline $…$ and block $$…$$ typeset via KaTeX → MathML:

import markedKatex from "marked-katex-extension";
// ...
marked.use(markedKatex({ throwOnError: false, output: "mathml", nonStandard: false }));

But the top-level markdown type row in the diagram-recipes skill (plugin/skills/diagram-recipes/SKILL.md:50) presents markdown as just:

| `markdown` | formatted prose (GFM, raw HTML) | markdown text | notes, summaries, docs |

No mention of LaTeX/KaTeX/$…$. An LLM author scanning the type table to pick a renderer gets zero signal that math works, so it defaults to plain text / code-fences and the math renders as a monospace blob.

The capability is described — but only buried in the explainer-template detail file, plugin/skills/diagram-recipes/panes-explainers.md:58-63 ("LaTeX math in markdown panes … renders via KaTeX→MathML"). That's gated behind the relativity/entropy explainer recipe; an author writing a standalone markdown pane (not following that template) never reaches it. So the discoverability gap is: the authoritative type table omits math, and the one mention is context-bound.

Impact: Math-heavy explainers look broken despite the capability being present and working.

Proposed fix:

1. Surface KaTeX in the type table. Update the markdown row in SKILL.md to read roughly: formatted prose (GFM, raw HTML, **+ LaTeX via $…$ / $$…$$ → KaTeX/MathML**). Optionally add a one-line inline example next to it. (The panes-explainers.md detail already has a good example block — the fix is mostly about making the table itself self-sufficient.)
2. Document the $ gotchas (not currently noted anywhere):
   • Standard delimiters are in effect, so a literal currency $ should be escaped as \$.
   • Inline $…$ needs no inner whitespace adjacent to the delimiters.
3. (verify) Output is MathML with no KaTeX CSS shipped — the renderer comment explicitly notes it ships no KaTeX web-fonts/stylesheet and relies on native MathML. Confirm equations actually render on target devices, especially iPad / Safari (native MathML support has historically been uneven). If shaky, consider output: "htmlAndMathml" and bundling the KaTeX stylesheet.

Quick repro: Push one markdown pane with $$\frac{a}{b}$$ and another with the same inside a code-fence — the first typesets, the second doesn't, and nothing in the type table tells you the first will work.