## What changed
- Render completed `mermaid` fences with `codex-mermaid`, using syntax-theme colors for nodes and edges.
- Keep source visible for unclosed, invalid, unsupported, or oversized diagrams, and preserve the original Mermaid for copying and raw mode.
- Keep streamed diagrams mutable until the next top-level block so closing fences and terminal resizing can update their display. Preserve scrollback progress across width and render-mode changes.
## Testing
Add renderer and streaming tests covering supported diagram families, nested fences, Unicode, theme colors, source fallbacks, resizing, raw-mode transitions, and original-source preservation. Verify that node connection ports retain node styling in all four flowchart directions.
GitOrigin-RevId: 9a759248110e6730d629d653061ff7e2ec5dc2c0
## What changed
Add `codex-mermaid`, a standalone crate that renders supported subsets of flowchart, sequence, state, class, and ER diagrams as Unicode text. Expose `render` for plain text and `render_spans` for semantic node, edge, and text spans that callers can style.
Enforce source, diagram, canvas, and display-width limits. Return errors for unsupported input or exceeded limits without producing partial diagrams, leaving source fallback to callers. Include documentation and a stdin rendering example.
## Testing
Add snapshots for each diagram family, checks for relationship endpoints, Unicode labels, semantic spans, truncated input, and size limits, plus edge reconstruction for all 512 directed three-node graphs in all four layout directions.
GitOrigin-RevId: 5b4e65d9152abce5d833e4e6b12113a5a21f700e
