Nearly every hard bug in the editor traced back to two competing sources of state — a global settings bucket and per-node data drifting out of sync. Deriving state from the node itself and writing through one path resolved entire classes of bugs at once.

Anything timing-sensitive — re-entrancy guards, drag state, dedup checks — needed to mutate synchronously. Async state updates left small windows where duplicate actions or race conditions could slip through.

React Flow's internal store and the app's own application state are separate systems. Reads and writes have to stay consistent with the same store, or the canvas silently desyncs from what the UI shows.

Binding chart nodes to live, polling data introduced its own failure modes — stale field paths, unmemoized chart options, missed series types. Getting live data onto the canvas reliably took as much care as the canvas itself.

Rebuilding history to read fresh state internally, rather than trusting values passed in from a render closure, eliminated a whole category of stale-snapshot bugs in undo/redo.

Details like using outline instead of border for selection indicators, or unifying dash-pattern handling across nodes and edges, mattered far more once diagrams grew large and dense with real site data.