fix(web): 修复历史消息加载时的滚动位置恢复问题

[0x7551]

问题描述

在加载历史消息时，自动滚动功能会干扰滚动位置的恢复。

修复内容

1. 防止 autoScroll 在历史加载时干扰滚动位置
2. 等待 DOM 更新完成后再恢复滚动位置

via HAPI

Co-Authored-By: HAPI noreply@hapi.run

[github-actions]

[MAJOR] UX 自动滚动状态被强制开启

Why this is a problem: 历史加载完成后即使用户不在底部也开启 autoScroll，下一条消息可能跳到底部，打断阅读。

Suggested fix:

const prevAutoScrollRef = useRef(true)

prevAutoScrollRef.current = autoScrollEnabledRef.current
setAutoScrollEnabled(false)

if (prevAutoScrollRef.current) {
    setAutoScrollEnabled(true)
}

[github-actions]

[MINOR] Performance requestAnimationFrame 无上限轮询

Why this is a problem: delta 长期为 0 时 rAF 递归不退出，持续排队，loadLock 也可能保持等待。

Suggested fix:

let attempts = 0
const MAX_ATTEMPTS = 5

const checkAndRestore = () => {
    if (!pendingScrollRef.current) return
    const delta = viewport.scrollHeight - pending.scrollHeight
    if (delta === 0 && attempts++ < MAX_ATTEMPTS) {
        requestAnimationFrame(checkAndRestore)
        return
    }
    viewport.scrollTop = pending.scrollTop + delta
    pendingScrollRef.current = null
    loadLockRef.current = false
}

[github-actions]

Findings

• [Major] 自动滚动被强制开启 — 历史加载完成后仍开启 autoScroll，用户不在底部也可能被拉到底部。证据 web/src/components/AssistantChat/HappyThread.tsx:272
  Suggested fix:

  const prevAutoScrollRef = useRef(true)
  
  prevAutoScrollRef.current = autoScrollEnabledRef.current
  setAutoScrollEnabled(false)
  
  if (prevAutoScrollRef.current) {
      setAutoScrollEnabled(true)
  }

• [Minor] requestAnimationFrame 无上限轮询 — delta 长期为 0 时 rAF 持续循环。证据 web/src/components/AssistantChat/HappyThread.tsx:263
  Suggested fix:

  let attempts = 0
  const MAX_ATTEMPTS = 5
  
  const checkAndRestore = () => {
      if (!pendingScrollRef.current) return
      const delta = viewport.scrollHeight - pending.scrollHeight
      if (delta === 0 && attempts++ < MAX_ATTEMPTS) {
          requestAnimationFrame(checkAndRestore)
          return
      }
      viewport.scrollTop = pending.scrollTop + delta
      pendingScrollRef.current = null
      loadLockRef.current = false
  }

Summary

• 2 issues: 自动滚动状态覆盖、rAF 无上限轮询；滚动体验与性能风险

Testing

• Not run (automation)

HAPI Bot

[0x7551]

Closing in favor of #170 (same fix, recreated PR due to stale head SHA sync issue).