fix(frontend): 稳定虚拟环境探测状态，避免输入时闪烁

探测状态保留上一次结果，新结果返回后再更新；空目录改为中性提示；防抖期间不因旧工作目录闪出警告；占位数据期间不自动回填虚拟环境。

frontend/src/components/TaskEditorModal.tsx

@@ -1,5 +1,10 @@
 import { zodResolver } from '@hookform/resolvers/zod'
-import { useMutation, useQuery, useQueryClient } from '@tanstack/react-query'
+import {
+  keepPreviousData,
+  useMutation,
+  useQuery,
+  useQueryClient,
+} from '@tanstack/react-query'
 import {
   Button,
   Checkbox,
@@ -209,6 +214,7 @@ export function TaskEditorModal({
       actionType === 'script' &&
       isPythonScript &&
       Boolean(debouncedWorkingDir.trim()),
+    placeholderData: keepPreviousData,
     retry: false,
     staleTime: 15_000,
   })
@@ -230,7 +236,9 @@ export function TaskEditorModal({
     onError: (error) => toast.error(error.message),
   })
   const linkedVenv =
-    isPythonScript && venvProbe.data?.status === 'linked'
+    isPythonScript &&
+    !venvProbe.isPlaceholderData &&
+    venvProbe.data?.status === 'linked'
       ? venvProbe.data
       : null
   const previewVirtualEnv = isPythonScript
@@ -270,7 +278,7 @@ export function TaskEditorModal({
 
   // 探测到虚拟环境就自动填进「虚拟环境目录」，但用户自己改过就保留用户的值。
   useEffect(() => {
-    if (!open || !isPythonScript) {
+    if (!open || !isPythonScript || venvProbe.isPlaceholderData) {
       return
     }
     const probe = venvProbe.data
@@ -295,7 +303,7 @@ export function TaskEditorModal({
       shouldDirty: true,
       shouldValidate: true,
     })
-  }, [debouncedVenv, debouncedWorkingDir, getValues, isPythonScript, open, setValue, venvProbe.data])
+  }, [debouncedVenv, debouncedWorkingDir, getValues, isPythonScript, open, setValue, venvProbe.data, venvProbe.isPlaceholderData])
 
   // 打开后把焦点给第一个可编辑字段：新建时是任务标识，编辑时 ID 已锁定，跳名称。
   // 原生 dialog 默认聚焦关闭按钮，不符合编辑表单的节奏。
@@ -595,7 +603,7 @@ export function TaskEditorModal({
                 </FormField>
 
                 <VenvDetectorBar
-                  workingDir={debouncedWorkingDir}
+                  workingDir={scriptPreview.working_dir}
                   probe={venvProbe.data}
                   pending={venvProbe.isPending}
                   failed={venvProbe.isError}
@@ -1013,25 +1021,29 @@ function VenvDetectorBar({
   if (!workingDir.trim()) {
     return (
       <div className="env-detector-bar" role="status">
-        <span className="env-status-badge warn">
-          ● 请输入有效的工作目录以探测环境
-        </span>
+        <span className="env-detector-hint">填写工作目录后自动检测环境</span>
       </div>
     )
   }
 
-  if (pending) {
+  if (!probe) {
+    if (pending) {
+      return (
+        <div className="env-detector-bar" role="status">
+          <span className="env-status-badge pending">⏳ 正在检测环境...</span>
+        </div>
+      )
+    }
+    if (failed) {
+      return (
+        <div className="env-detector-bar" role="status">
+          <span className="env-status-badge warn">● 环境探测失败，可稍后重试</span>
+        </div>
+      )
+    }
     return (
       <div className="env-detector-bar" role="status">
-        <span className="env-status-badge pending">⏳ 正在探测解释器...</span>
-      </div>
-    )
-  }
-
-  if (failed || !probe) {
-    return (
-      <div className="env-detector-bar" role="status">
-        <span className="env-status-badge warn">● 环境探测失败，可稍后重试</span>
+        <span className="env-detector-hint">正在检测环境...</span>
       </div>
     )
   }