From e04995a84d3134ce91ef52e3463bd06a5e434758 Mon Sep 17 00:00:00 2001
From: AskaEth <i@yeij.top>
Date: Tue, 8 Sep 2026 21:16:49 +0800
Subject: [PATCH] =?UTF-8?q?fix(chat):=20=E6=96=B0=E6=B6=88=E6=81=AF?=
 =?UTF-8?q?=E8=87=AA=E5=8A=A8=E8=B7=9F=E9=9A=8F=E5=BA=95=E9=83=A8=EF=BC=88?=
 =?UTF-8?q?=E5=BE=AE=E4=BF=A1/QQ=20=E5=BC=8F=EF=BC=89?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

reverseLayout 会锚定原可见项，导致新消息插到视口外。改为：滚动结束时记录是否贴底（容差 64px），最新一项变化且处于跟随状态时 animateScrollToItem(0)；用户上滑查看历史时不再强制滚动。
---
 .../top/yeij/cyrene/ui/chat/ChatScreen.kt     | 28 +++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/app/src/main/kotlin/top/yeij/cyrene/ui/chat/ChatScreen.kt b/app/src/main/kotlin/top/yeij/cyrene/ui/chat/ChatScreen.kt
index 7f4bec4..47de3f3 100644
--- a/app/src/main/kotlin/top/yeij/cyrene/ui/chat/ChatScreen.kt
+++ b/app/src/main/kotlin/top/yeij/cyrene/ui/chat/ChatScreen.kt
@@ -18,6 +18,9 @@ import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.collectAsState
 import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
 import androidx.compose.runtime.snapshotFlow
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
@@ -40,6 +43,9 @@ import top.yukonga.miuix.kmp.icon.MiuixIcons
 import top.yukonga.miuix.kmp.icon.basic.Sidebar
 import top.yukonga.miuix.kmp.theme.MiuixTheme
 
+/** 判定「贴着底部」的容差（px）。 */
+private const val BOTTOM_TOLERANCE = 64
+
 @Composable
 fun ChatScreen(
     container: AppContainer,
@@ -52,6 +58,28 @@ fun ChatScreen(
     val state by viewModel.state.collectAsState()
     val listState = rememberLazyListState()
 
+    // 是否跟随底部（微信/QQ 式）：只有用户主动滚到别处时才停止跟随。
+    // 只在「滚动结束」时更新，避免新消息插入导致的锚点位移把状态带偏。
+    var followBottom by remember { mutableStateOf(true) }
+    LaunchedEffect(listState) {
+        snapshotFlow { listState.isScrollInProgress }
+            .distinctUntilChanged()
+            .collect { scrolling ->
+                if (!scrolling) {
+                    followBottom = listState.firstVisibleItemIndex == 0 &&
+                        listState.firstVisibleItemScrollOffset < BOTTOM_TOLERANCE
+                }
+            }
+    }
+
+    // 最新一项变化（新消息 / 乐观气泡 / 流式气泡 / 落库归一）时，跟随则滚到底。
+    val newestKey = state.items.lastOrNull()?.key
+    LaunchedEffect(newestKey) {
+        if (newestKey != null && followBottom) {
+            listState.animateScrollToItem(0)
+        }
+    }
+
     // reverseLayout 下「列表末尾」就是屏幕顶部；接近末尾时加载更早的一页。
     LaunchedEffect(listState) {
         snapshotFlow {