tl;dr: Whiteboard is an open-source (MIT) desktop IDE that lets coding agents like Claude Code and Codex draw diagrams, sequence charts, and decision logs on a shared canvas linked directly to your code. Built on a vendored Code OSS fork, it includes a Rust-based semantic AST-aware diff viewer that collapses noise like tests and docs, and lets you click visualizations to jump to the underlying source. It runs against local checkouts; file editing and multi-repo reviews aren't yet supported.