✨ feat(vscode): 文件和文件夹在预览顶部问

侧栏「问 AI」打开代码阅读预览。文件夹是没有代码块的一页，源码文件在整页顶部聊，代码块下面的问答不动。历史按工作区文件夹和相对路径记在窗口状态里，不写进按块存的记录。

vscode/webview-ui/src/codeReader/qa.test.ts

@@ -1,7 +1,7 @@
 import type { QaAction, QaState } from './qa'
 import type { QaMessage, QaThreadView } from './types'
 import { describe, expect, it } from 'vitest'
-import { answerPreview, asksOf, EMPTY_QA, historyOf, qaReducer, relativeTime } from './qa'
+import { answerPreview, asksOf, EMPTY_QA, historyOf, PATH_ASK_ANCHOR, qaReducer, relativeTime } from './qa'
 
 const IF = 'function get_user > if @3fa1c2d0'
 
@@ -10,7 +10,7 @@ function thread(anchor: string, ...ids: string[]): QaThreadView {
 }
 
 function message(threads: QaThreadView[], running: QaMessage['running'] = []): QaMessage {
-  return { type: 'qa', available: true, threads, running }
+  return { type: 'qa', available: true, threads, path: [], subject: 'file', running }
 }
 
 function qa(threads: QaThreadView[], running: QaMessage['running'] = []): QaAction {
@@ -42,6 +42,24 @@ describe('问 AI 的状态', () => {
     expect(state.threads).toHaveLength(1)
   })
 
+  it('顶部的问答记在路径上，不进任何一块的历史', () => {
+    const state = run({
+      type: 'qa',
+      message: {
+        type: 'qa',
+        available: true,
+        threads: [],
+        path: [{ id: 'p', question: '这文件夹干什么', answer: '放源码', createdAt: '2026-09-25T10:00:00.000Z' }],
+        subject: 'folder',
+        running: [],
+      },
+    })
+    expect(state.path.map(entry => entry.id)).toEqual(['p'])
+    expect(state.subject).toBe('folder')
+    expect(historyOf(state, PATH_ASK_ANCHOR).map(entry => entry.id)).toEqual(['p'])
+    expect(historyOf(state, IF)).toEqual([])
+  })
+
   it('收起就结束这一轮：答完的回到历史，还在答的留着；再展开', () => {
     let state = run(
       qa([thread(IF, 'e1')]),