- New diagram agent: Planner generates Mermaid code, Responder explains
- FastAPI route: /api/diagram/chat + /clear with Redis session history
- Frontend: split-pane UI with canvas pan/zoom (scroll wheel + drag)
- Auto-fit diagram to view, grid background, PNG export
- Prompt enforces ASCII syntax labels for Mermaid compatibility
- Planner LLM max_tokens=4000 for complex diagram generation
- Supports: flowchart, sequence, class, ER, gantt, mindmap, pie chart