updateWhiteboardScene

Edit elements on a whiteboard's canvas WITHOUT dropping the rest of the scene. A board may hold many diagrams/elements, so prefer surgical edits: mode='patch' (DEFAULT) shallow-merges each incoming object into the existing element with the same id (send just {id, backgroundColor:'blue'} to recolour one box, or {id, x, y} to move one) and appends any elements whose id is new/absent — everything else is left untouched. deleteIds removes specific elements by id. mode='append' only adds. mode='replace' overwrites the ENTIRE scene — to rebuild or edit only PART of a board, still use 'patch', because replace DELETES every element you don't resend (of ANY type). As a safeguard, a replace that would drop ANY existing element not in your payload is REJECTED unless you pass confirmReplace:true (or include those ids); diagrams/images/frames are flagged specially since they're inserted separately and costliest to lose. To author NEW shapes/connectors from a high-level spec, prefer addWhiteboardElements — and prefer library stencils / sticky notes / architecture icons over plain rectangles wherever a standard form fits (sticky notes, kanban/scrum, flowcharts, UML/ER, BPMN, org charts, wireframes). Optional appState/files are merged in. PROCESS: for a non-trivial edit call getWhiteboardGuide FIRST; after editing, ALWAYS call getWhiteboardImage to confirm the board still looks right (layout, labels, overlaps), and patch again if it doesn't.