docs(tests): clarify validation ownership and digest lifecycle checks

tests/headless/element-validation.test.mjs

@@ -25,12 +25,14 @@ test('editor creations detach caller data; topology-only validation cannot bypas
  const f=setup();let id=0;const editor=createEditor({document:f.document,registry:f.registry,createId:()=>`op-${++id}`}),incoming=node('new');assert.equal(editor.dispatch({type:'element.create',element:incoming}).status,'applied');incoming.geometry.width=-1;incoming.data.text=undefined;const record=editor.getSnapshot().document.elements.get('new');assert.equal(record.geometry.width,100);assert.equal(record.data.text,'hello');const fresh=createDocument('p',[{id:'root',parent:null}],[node('topology')]).elements.get('topology');f.allow(false);const calls=f.calls();validateElementRecord(fresh,f.registry,new Map(),false);assert.equal(f.calls(),calls);assert.throws(()=>validateElementRecord(fresh,f.registry),/invalid_component_data/);editor.dispose();
 });
 
-// 用空canvas、墓碑、缺端点及非法几何比较两种遍历结果，再检查合法迭代器的让步步数。
+// 用空 canvas、墓碑、缺端点及非法几何比较两种遍历的首个拒绝结果，再检查合法迭代器的让步步数。
+// outcome 只观察 code/targets，没有记录所有校验步骤；相同结果不能单独证明内部每一步的执行顺序。
 test('synchronous and cooperative validation preserve check order and the same rejection results',()=>{
  const f=setup(),base=f.document,edge={id:'edge',incarnation:1,ownerCanvasId:'root',componentId:'connection',dataVersion:1,structure:'connection',data:{},source:{elementId:'a'},target:{elementId:'missing'},path:null},cases=[base,{...base,canvases:new Map()}, {...base,tombstones:new Map([['a',0]])},{...base,tombstones:new Map([['a',1]])},{...base,canvases:new Map([['root',{id:'root',parent:null}],['other',{id:'other',parent:null}]])},createDocument('p',[{id:'root',parent:null}],[node(),edge]),createDocument('p',[{id:'root',parent:null}],[{...node(),geometry:{...node().geometry,width:0}}])];
  /** 将抛错规范为code/targets或valid，比较同步与协作遍历的拒绝结果，而非依赖异常对象引用。 */
  const outcome=callback=>{try{callback();return'valid';}catch(error){return{code:error.code,targets:error.targets};}};
  for(const document of cases)assert.deepEqual(outcome(()=>validateDocument(document,f.registry)),outcome(()=>{for(const _ of validateDocumentSteps(document,f.registry)){};}));
+ // base 仅含一张 canvas 和一个元素：两次 next 各让出一次，第三次报告完成；这里不测帧耗时。
  const iterator=validateDocumentSteps(base,f.registry);assert.deepEqual(iterator.next(),{done:false,value:undefined});assert.deepEqual(iterator.next(),{done:false,value:undefined});assert.equal(iterator.next().done,true);
 });