ADR-011: Frontend-only Markdown/Mermaid rendering

Status: Accepted

Context

Open Question 15: is POST /plans/render needed, or can rendering stay in React?

Decision

Render Markdown and Mermaid in the renderer with bundled libraries (react-markdown, remark-gfm, mermaid, dompurify) — no CDN, works offline. The backend only persists raw plan text; there is no /plans/render endpoint. Mermaid runs with securityLevel: "strict" and its SVG output is sanitized with DOMPurify. Invalid Mermaid preserves the source and shows an explicit error.

Consequences

• No duplicated rendering semantics across Python and React.
• Offline plan preview works with no network dependency.