9eba62c5b5
Root cause: handleAddNode/handleEdgeConfirm only updated Zustand store, never creating records in the DB. canvasApi.save() only updated positions of existing nodes, so nothing survived a page refresh. Fix: save now sends the full canvas state (all nodes + edges + data) and the backend does a full sync — upsert incoming, delete anything removed. This means Save is the single source of truth: no need to call individual create/update/delete APIs for every drag or edit.