编辑器体验改进

- 导入文件后直接关闭弹窗 + toast 提示导入数量
- 自动布局改为按出口顺序的子树居中：选项1/2/3 分支顺序正确且对齐

web/static/graph.js

@@ -91,21 +91,36 @@
     (ir.nodes || []).forEach(n => nodes[n.id] = n);
     (ir.endings || []).forEach(e => nodes[e.id] = e);
     const ids = Object.keys(nodes);
+    // 层级：最长路径（决定横向 x，左→右）
     const edges = [];
-    (ir.nodes || []).forEach(n => rawTargets(n).forEach(t => { if (t && nodes[t]) edges.push([n.id, t]); }));
+    ids.forEach(id => rawTargets(nodes[id]).forEach(t => { if (t && nodes[t]) edges.push([id, t]); }));
     const layer = {}; ids.forEach(id => layer[id] = 0);
     let changed = true, guard = 0;
     while (changed && guard++ < 9999) {
       changed = false;
       edges.forEach(([u, v]) => { if (layer[v] < layer[u] + 1) { layer[v] = layer[u] + 1; changed = true; } });
     }
-    const perLayer = {}, pos = {};
-    ids.forEach(id => {
-      const l = layer[id]; perLayer[l] = perLayer[l] || 0;
-      // 横向分层（左→右），契合 Drawflow 端口左右朝向
-      pos[id] = { x: 40 + l * COL, y: 30 + perLayer[l] * ROW };
-      perLayer[l]++;
-    });
+    // 有序子表（按出口顺序，去重）+ 入度求根
+    const childMap = {}, indeg = {}; ids.forEach(id => { childMap[id] = []; indeg[id] = 0; });
+    const seen = new Set();
+    ids.forEach(id => rawTargets(nodes[id]).forEach(t => {
+      if (t && nodes[t]) { const k = id + ">" + t; if (!seen.has(k)) { seen.add(k); childMap[id].push(t); indeg[t]++; } }
+    }));
+    let roots = ids.filter(id => indeg[id] === 0);
+    if (!roots.length && ids.length) roots = [ids[0]];
+    // 子树居中：按出口顺序递归分配纵向 y，父节点居子范围中点 → 选项1上/2中/3下且对齐
+    const ypos = {}; let nextY = 0; const vis = new Set();
+    function assignY(id) {
+      if (!id || vis.has(id)) return; vis.add(id);
+      if (!childMap[id].length) { ypos[id] = nextY; nextY += ROW; return; }
+      childMap[id].forEach(assignY);
+      const placed = childMap[id].map(c => ypos[c]).filter(v => v !== undefined);
+      ypos[id] = placed.length ? (Math.min(...placed) + Math.max(...placed)) / 2 : (nextY += ROW, nextY - ROW);
+    }
+    roots.forEach(assignY);
+    ids.forEach(id => { if (ypos[id] === undefined) { ypos[id] = nextY; nextY += ROW; } });
+    const pos = {};
+    ids.forEach(id => { pos[id] = { x: 40 + layer[id] * COL, y: 30 + ypos[id] }; });
     return pos;
   }
   function ensureLayout(ir) {