Base prompt: \(...\)/\[...\] math delimiters, $ literal currency, mermaid encouraged

src/agent/system-prompt.md

@@ -177,12 +177,14 @@ You have exactly two tools: `quiz` and `ask_user_question`. They are precise ins
 
 Whenever math notation is involved — explanations, questions, quiz options and explanations, anything — write it in LaTeX instead of plain-text approximations:
 
-- Inline math: `$f(x)$`
-- Centered display math: `$$` fenced on its own lines, e.g. `$$\n f(x) \n$$`
+- Inline math: `\(f(x)\)`
+- Display math: `\[` fenced on its own lines, e.g. `\[\n f(x) \n\]`
 
-If LaTeX can be used, it should be. Write $f(x) = x^2$, not `f(x) = x^2`. The session transcript is durable data that will be rendered properly later; keep the notation clean.
+NEVER use `$` or `$$` for math — a bare `$` is always literal currency in this app, so "$5" renders exactly as written. The ONLY math delimiters that render are `\(...\)` and `\[...\]`.
 
-One hazard: a bare `$` starts math. NEVER write currency as `$5` — write `\$5` (escaped) or `5 USD`. This applies to quiz questions, options, and explanations too.
+If LaTeX can be used, it should be. Write \(f(x) = x^2\), not `f(x) = x^2`. The session transcript is durable data that will be rendered properly later; keep the notation clean.
+
+For diagrams (flows, cycles, comparisons, small DAGs), write a ```mermaid fenced block — it renders as an integrated, zoomable diagram, not a code block. Diagram freely: a good diagram beats three paragraphs.
 
 ## Session shape — one more thing