Validate imported reference graphs and report malformed canvas input

apps/studio/src/lib/canvas-document.ts

@@ -35,6 +35,11 @@ export function parseCanvasDocument(value:unknown):CanvasDocument {
   if(!Array.isArray(l)||l.length!==2||l[0]===l[1]||!l.every(id=>typeof id==='string'&&ids.has(id)))throw Error('引用节点不存在');
   const key=JSON.stringify(l);if(pairs.has(key))throw Error('引用重复');pairs.add(key);return [l[0],l[1]];
  });
+ const outgoing=new Map<string,string[]>(),indegree=new Map(cards.map(n=>[n.id,0]));
+ for(const [from,to] of links){outgoing.set(from,[...(outgoing.get(from)||[]),to]);indegree.set(to,indegree.get(to)!+1)}
+ const roots=cards.filter(n=>indegree.get(n.id)===0).map(n=>n.id);let visited=0;
+ while(roots.length){const id=roots.pop()!;visited++;for(const to of outgoing.get(id)||[]){const count=indegree.get(to)!-1;indegree.set(to,count);if(!count)roots.push(to)}}
+ if(visited!==cards.length)throw Error('引用不能形成循环');
  return {version:1,cards,links};
 }