fix(frontend): TaskFlowView 根治双重渲染 — allMains 仅含根级节点

生产数据问题：16个任务中15个TRANSFER子节点全部挂在同一个root下，
isMain() 将它们同时放入 allMains 和 childMap，导致每个子节点渲染2次。

修复:
1. allMains 改为仅收集 parent_task_id IS NULL 的根级主干
   - TRANSFER 子节点仅通过 childMap → renderBranch 递归渲染
   - 彻底杜绝同一任务在时间线 + 分支中双重出现
2. 统一焦点/全景为同一套垂直时间线 JSX 布局
   - 删除旧焦点模式的独立 flex-row 排版
   - visibleMains useMemo 负责数据过滤 (active() 过滤)
3. 清理死代码: getRootMainId() / rootMainMap / srm / flatMap

frontend/src/components/TaskTree/TaskFlowView.tsx

@@ -13,16 +13,6 @@ import type { ModalTarget } from "./TaskTreeViewer";
 // ============================================================
 function fmtTime(d: string | null) { if (!d) return ""; const dt = new Date(d); const pad = (n: number) => String(n).padStart(2, "0"); return `${dt.getFullYear()}-${pad(dt.getMonth() + 1)}-${pad(dt.getDate())} ${pad(dt.getHours())}:${pad(dt.getMinutes())}`; }
 function isMain(t: TaskResponse) { return !t.parent_task_id || t.task_type === "TRANSFER" || t.task_type === "RECOVERY"; }
-/** 寻根算法：从任意任务向上攀爬，找到最近的视觉主干节点 ID */
-function getRootMainId(t: TaskResponse, flatMap: Record<string, TaskResponse>): string {
-  let curr: TaskResponse = t;
-  while (curr.parent_task_id && flatMap[curr.parent_task_id]) {
-    const p = flatMap[curr.parent_task_id];
-    if (isMain(p)) return p.id;
-    curr = p;
-  }
-  return curr.parent_task_id || curr.id;
-}
 function active(s: string) { return s === "WIP" || s === "PENDING"; }
 /** 微型右箭头 SVG */
 function ArrowRight({ color = "#9ca3af" }: { color?: string }) {
@@ -108,34 +98,16 @@ export const TaskFlowView = memo(function TaskFlowView({ tasks, onAction, curren
   const [showFullMap, setShowFullMap] = useState(false);
   const [recordsTask, setRecordsTask] = useState<TaskResponse | null>(null);
 
-  // 数据分类 — 🚀 虚拟扁平化：三层+嵌套协助统一挂在视觉主干下
-  const { activeMain, historicalMain, childMap, rootMainMap } = useMemo(() => {
+  // 数据分类 — 🚀 仅根级主干作为垂直时间线节点，子节点通过 childMap 分支递归渲染
+  const { allMains, childMap } = useMemo(() => {
     ALL_TASKS.clear(); if (tasks.length) collectAll(tasks);
     const all = Array.from(ALL_TASKS);
-    // 拍平映射
-    const flatMap: Record<string, TaskResponse> = {};
-    for (const t of all) flatMap[t.id] = t;
-    // 计算每个 sub 任务的视觉根主干 ID
-    const rootMap: Record<string, string> = {};
-    const srm: Record<string, TaskResponse[]> = {};
-    const am: TaskResponse[] = []; const hm: TaskResponse[] = [];
+    // 🔧 仅收集根级主干节点（parent_task_id IS NULL），杜绝 TRANSFER 子节点双重渲染
+    const mains: TaskResponse[] = [];
     for (const t of all) {
-      if (isMain(t)) {
-        if (active(t.status)) am.push(t); else hm.push(t);
-        srm[t.id] = [];
-      }
+      if (!t.parent_task_id && isMain(t)) mains.push(t);
     }
-    // 非主线任务：按根主干分组
-    for (const t of all) {
-      if (isMain(t)) continue;
-      const rootId = getRootMainId(t, flatMap);
-      rootMap[t.id] = rootId;
-      if (!srm[rootId]) srm[rootId] = [];
-      srm[rootId].push(t);
-    }
-    // 排序
-    am.sort((a, b) => new Date(a.created_at).getTime() - new Date(b.created_at).getTime());
-    hm.sort((a, b) => new Date(a.created_at).getTime() - new Date(b.created_at).getTime());
+    mains.sort((a, b) => new Date(a.created_at).getTime() - new Date(b.created_at).getTime());
     // 🚀 构建全局 childMap（按 parent_task_id 索引直接子节点，保留真实树结构）
     const childMap: Record<string, TaskResponse[]> = {};
     for (const t of all) {
@@ -144,11 +116,9 @@ export const TaskFlowView = memo(function TaskFlowView({ tasks, onAction, curren
       childMap[pid].push(t);
     }
     Object.values(childMap).forEach(arr => arr.sort((a, b) => new Date(a.created_at).getTime() - new Date(b.created_at).getTime()));
-    return { activeMain: am, historicalMain: hm, childMap, rootMainMap: rootMap };
+    return { allMains: mains, childMap };
   }, [tasks]);
 
-  const allMains = [...historicalMain, ...activeMain];
-
   // 🚀 递归渲染分支节点 — 每个节点从自己的 childMap 获取直系子孙，保持树结构不断裂
   const renderBranch = (node: TaskResponse, side: 'left' | 'right', isLegacy: boolean, rootMainId: string): JSX.Element => {
     const kids = childMap[node.id] || [];
@@ -172,6 +142,13 @@ export const TaskFlowView = memo(function TaskFlowView({ tasks, onAction, curren
     );
   };
 
+  // 🚀 焦点模式 vs 全景模式：共用同一套垂直时间线布局，仅数据过滤不同
+  const visibleMains = useMemo(() => {
+    if (showFullMap) return allMains;
+    // 焦点模式：过滤掉已完成/已入库的历史主线，保留活跃主线 + 所有协助分支
+    return allMains.filter(t => active(t.status));
+  }, [allMains, showFullMap]);
+
   return (
     <div>
       {/* 模式切换 */}
@@ -182,78 +159,51 @@ export const TaskFlowView = memo(function TaskFlowView({ tasks, onAction, curren
         </button>
       </div>
 
-      {/* ─── 焦点模式 ─── */}
-      {!showFullMap && (
-        <div className="flex flex-col items-center gap-4">
-          {activeMain.map(mainTask => {
-            const directChildren = childMap[mainTask.id] || [];
-            const leftDirect = directChildren.filter((_, i) => i % 2 === 0);
-            const rightDirect = directChildren.filter((_, i) => i % 2 === 1);
-            const isLegacy = !active(mainTask.status);
-            return (
-              <div key={mainTask.id} className="flex flex-row items-start w-full">
+      {/* ─── 统一垂直时间线布局（焦点/全景共用） ─── */}
+      <div className="space-y-6">
+        {visibleMains.map(mainTask => {
+          const directChildren = childMap[mainTask.id] || [];
+          const hasLegacyActive = directChildren.some(c => !isMain(c) && !active(mainTask.status));
+          const leftDirect = directChildren.filter((_, i) => i % 2 === 0);
+          const rightDirect = directChildren.filter((_, i) => i % 2 === 1);
+          const lineStyle = hasLegacyActive && !active(mainTask.status);
+
+          return (
+            <div key={mainTask.id} className="relative">
+              <div className="absolute left-1/2 top-0 bottom-0 w-0.5 bg-gray-200 -translate-x-1/2 z-0" />
+              <div className="flex flex-row items-start w-full">
                 {/* 左翼 — 递归渲染，子子孙孙向外延伸 */}
                 <div className="flex-1 flex flex-col items-end justify-center gap-2 pr-2">
-                  {leftDirect.map(t => renderBranch(t, 'left', isLegacy, mainTask.id))}
+                  {leftDirect.map(c => renderBranch(c, 'left', lineStyle, mainTask.id))}
                 </div>
-                {/* 中央主干 */}
-                <div className="shrink-0 z-10">
-                  <SlimCard task={mainTask} active assigneeName={assigneeNames?.[mainTask.assignee_id || ""]} onAction={onAction} currentUser={currentUser} onViewRecords={setRecordsTask} />
+                {/* 中央 */}
+                <div className="shrink-0 z-10 relative">
+                  <SlimCard task={mainTask} active={active(mainTask.status)}
+                    assigneeName={assigneeNames?.[mainTask.assignee_id || ""]} onAction={onAction} currentUser={currentUser} onViewRecords={setRecordsTask} />
+                  {active(mainTask.status) && (
+                    <div className="absolute -top-1 -left-1 h-3 w-3 rounded-full bg-green-400 border-2 border-white" />
+                  )}
                 </div>
                 {/* 右翼 — 递归渲染，子子孙孙向外延伸 */}
                 <div className="flex-1 flex flex-col items-start justify-center gap-2 pl-2">
-                  {rightDirect.map(t => renderBranch(t, 'right', isLegacy, mainTask.id))}
+                  {rightDirect.map(c => renderBranch(c, 'right', lineStyle, mainTask.id))}
                 </div>
               </div>
-            );
-          })}
-          {activeMain.length === 0 && <p className="text-xs text-gray-400 py-4">当前无活跃主线任务</p>}
-        </div>
-      )}
 
-      {/* ─── 全景模式 ─── */}
-      {showFullMap && (
-        <div className="space-y-6">
-          {allMains.map(mainTask => {
-            const directChildren = childMap[mainTask.id] || [];
-            const hasLegacyActive = directChildren.some(c => !isMain(c) && !active(mainTask.status));
-            const leftDirect = directChildren.filter((_, i) => i % 2 === 0);
-            const rightDirect = directChildren.filter((_, i) => i % 2 === 1);
-            const lineStyle = hasLegacyActive && !active(mainTask.status);
-
-            return (
-              <div key={mainTask.id} className="relative">
-                <div className="absolute left-1/2 top-0 bottom-0 w-0.5 bg-gray-200 -translate-x-1/2 z-0" />
-                <div className="flex flex-row items-start w-full">
-                  {/* 左翼 — 递归渲染，子子孙孙向外延伸 */}
-                  <div className="flex-1 flex flex-col items-end justify-center gap-2 pr-2">
-                    {leftDirect.map(c => renderBranch(c, 'left', lineStyle, mainTask.id))}
-                  </div>
-                  {/* 中央 */}
-                  <div className="shrink-0 z-10 relative">
-                    <SlimCard task={mainTask} active={active(mainTask.status)}
-                      assigneeName={assigneeNames?.[mainTask.assignee_id || ""]} onAction={onAction} currentUser={currentUser} onViewRecords={setRecordsTask} />
-                    {active(mainTask.status) && (
-                      <div className="absolute -top-1 -left-1 h-3 w-3 rounded-full bg-green-400 border-2 border-white" />
-                    )}
-                  </div>
-                  {/* 右翼 — 递归渲染，子子孙孙向外延伸 */}
-                  <div className="flex-1 flex flex-col items-start justify-center gap-2 pl-2">
-                    {rightDirect.map(c => renderBranch(c, 'right', lineStyle, mainTask.id))}
-                  </div>
+              {visibleMains.indexOf(mainTask) < visibleMains.length - 1 && (
+                <div className="flex justify-center py-2">
+                  <span className="text-[10px] text-gray-300">▼</span>
                 </div>
-
-                {allMains.indexOf(mainTask) < allMains.length - 1 && (
-                  <div className="flex justify-center py-2">
-                    <span className="text-[10px] text-gray-300">▼</span>
-                  </div>
-                )}
-              </div>
-            );
-          })}
-          {allMains.length === 0 && <p className="text-center text-xs text-gray-400 py-8">暂无流转记录</p>}
-        </div>
-      )}
+              )}
+            </div>
+          );
+        })}
+        {visibleMains.length === 0 && (
+          <p className="text-center text-xs text-gray-400 py-8">
+            {showFullMap ? "暂无流转记录" : "当前无活跃主线任务"}
+          </p>
+        )}
+      </div>
 
       {/* 记录弹窗 */}
       {recordsTask && (