fix(canvas): 节点间连线去重并放大弯折点

frontend/src/components/canvas/CanvasStage.vue

@@ -726,7 +726,7 @@ defineExpose({
             class="cv-edge-bend"
             :cx="p.handle.x"
             :cy="p.handle.y"
-            r="5"
+            r="8"
           />
         </g>
       </svg>

frontend/src/utils/canvas.js

@@ -123,10 +123,14 @@ export function normalizeDoc(raw) {
     }
   }
   if (Array.isArray(raw.edges)) {
+    const pairs = new Set() // 同一对节点只保留一条线(旧文档可能有重复)
     for (const e of raw.edges) {
       if (!e || typeof e.id !== 'string') continue
       if (typeof e.from !== 'string' || typeof e.to !== 'string') continue
       if (!ids.has(e.from) || !ids.has(e.to) || e.from === e.to) continue
+      const pair = e.from < e.to ? `${e.from}|${e.to}` : `${e.to}|${e.from}`
+      if (pairs.has(pair)) continue
+      pairs.add(pair)
       const edge = { id: e.id, from: e.from, to: e.to }
       if (['top', 'right', 'bottom', 'left'].includes(e.fromSide)) edge.fromSide = e.fromSide
       if (['top', 'right', 'bottom', 'left'].includes(e.toSide)) edge.toSide = e.toSide

frontend/src/views/CanvasView.vue

@@ -378,7 +378,8 @@ function deleteSelection() {
 
 // ---- 手动连线 ----
 function onLinkCreate({ from, to, fromSide, toSide }) {
-  if (doc.edges.some((e) => e.from === from && e.to === to)) return // 去重
+  // 任意方向去重:两个节点之间只允许一条连线
+  if (doc.edges.some((e) => (e.from === from && e.to === to) || (e.from === to && e.to === from))) return
   doc.edges.push({ id: newId('e'), from, to, fromSide, toSide })
   pushHistory()
 }