diff --git a/.github/workflows/sync-upstream.yml b/.github/workflows/sync-upstream.yml
new file mode 100644
index 00000000..9e9bc802
--- /dev/null
+++ b/.github/workflows/sync-upstream.yml
@@ -0,0 +1,44 @@
+name: Upstream Sync
+
+permissions:
+  contents: write
+
+on:
+  schedule:
+    - cron: "0 0 * * *" # 每天 UTC 时间 0点 (北京时间早上8点) 自动执行
+  workflow_dispatch:
+
+jobs:
+  sync_with_upstream:
+    name: Sync with Upstream
+    runs-on: ubuntu-latest
+    if: ${{ github.event.repository.fork }} # 仅在当前仓库是 Fork 的仓库时运行
+
+    steps:
+      - name: Checkout target branch
+        uses: actions/checkout@v3
+
+      - name: Sync Upstream
+        uses: aormsby/Fork-Sync-With-Upstream-action@v3.4
+        with:
+
+          # 1. 设置上游仓库地址 (格式：用户名/仓库名)
+          upstream_sync_repo: LagrangeDev/LagrangeV2
+
+          # 2. 设置上游仓库的分支 (通常是 main 或 master)
+          upstream_sync_branch: main
+
+          # 3. 设置您当前仓库需要更新的分支
+          target_sync_branch: main
+          
+          # --- 配置结束 ---
+
+          target_repo_token: ${{ secrets.GITHUB_TOKEN }}
+          test_mode: false
+
+      - name: Check for Failure
+        if: failure()
+        run: |
+          echo "[Error] 由于存在冲突，自动同步失败。"
+          echo "请手动解决冲突：git pull upstream main 并在本地合并后推送。"
+          exit 1
diff --git a/Lagrange.Core/Common/Entity/BotGroup.cs b/Lagrange.Core/Common/Entity/BotGroup.cs
index 20ad0c3d..4af526b8 100644
--- a/Lagrange.Core/Common/Entity/BotGroup.cs
+++ b/Lagrange.Core/Common/Entity/BotGroup.cs
@@ -8,7 +8,8 @@ public class BotGroup(
     long createTime,
     string? description,
     string? question,
-    string? announcement) : BotContact
+    string? announcement,
+    uint lastestSeq = 0) : BotContact
 {
     public long GroupUin { get; } = groupUin;
 
@@ -25,6 +26,11 @@ public class BotGroup(
     public string? Question { get; } = question;
 
     public string? Announcement { get; } = announcement;
+
+    /// <summary>
+    /// The latest message sequence number for this group.
+    /// </summary>
+    public uint LastestSeq { get; } = lastestSeq;
     
     public override long Uin => GroupUin;
 
diff --git a/Lagrange.Core/Internal/Services/System/FetchGroupsService.cs b/Lagrange.Core/Internal/Services/System/FetchGroupsService.cs
index 8ff696f5..36a35c50 100644
--- a/Lagrange.Core/Internal/Services/System/FetchGroupsService.cs
+++ b/Lagrange.Core/Internal/Services/System/FetchGroupsService.cs
@@ -38,7 +38,8 @@ private protected override Task<FetchGroupsEventResp> ProcessResponse(FetchGroup
                 raw.Info.CreatedTime,
                 raw.Info.Description,
                 raw.Info.Question,
-                raw.Info.Announcement
+                raw.Info.Announcement,
+                raw.CustomInfo?.LastestSeq ?? 0
             ))]));
     }
 }
\ No newline at end of file
diff --git a/Lagrange.Core/Message/Entities/MultiMsgEntity.cs b/Lagrange.Core/Message/Entities/MultiMsgEntity.cs
index 44be011c..d7aca564 100644
--- a/Lagrange.Core/Message/Entities/MultiMsgEntity.cs
+++ b/Lagrange.Core/Message/Entities/MultiMsgEntity.cs
@@ -26,9 +26,34 @@ public async Task Preprocess(BotContext context, BotMessage message)
     {
         if (string.IsNullOrEmpty(ResId))
         {
+            // Recursively preprocess internal messages
+            Console.WriteLine($"[MultiMsgEntity] Preprocessing {Messages.Count} messages for forward chain...");
+            
+            foreach (var innerMsg in Messages)
+            {
+                foreach (var entity in innerMsg.Entities)
+                {
+                    try 
+                    {
+                        await entity.Preprocess(context, message);
+
+                        if (entity is ImageEntity img)
+                        {
+                            if (img.MsgInfo != null)
+                                Console.WriteLine($"[MultiMsgEntity] Image uploaded successfully. Size: {img.ImageSize}");
+                            else
+                                Console.WriteLine("[MultiMsgEntity] WARNING: Image MsgInfo is NULL after preprocess!");
+                        }
+                    }
+                    catch (Exception ex)
+                    {
+                        Console.WriteLine($"[MultiMsgEntity] Error preprocessing entity: {ex.Message}");
+                    }
+                }
+            }
+
             var result = await context.EventContext.SendEvent<LongMsgSendEventResp>(new LongMsgSendEventReq(message.Receiver, Messages));
             ResId = result.ResId;
-
         }
     }
     
diff --git a/Lagrange.Milky/Api/Handler/Message/GetHistoryMessagesHandler.cs b/Lagrange.Milky/Api/Handler/Message/GetHistoryMessagesHandler.cs
index 5d64ced2..39eedc21 100644
--- a/Lagrange.Milky/Api/Handler/Message/GetHistoryMessagesHandler.cs
+++ b/Lagrange.Milky/Api/Handler/Message/GetHistoryMessagesHandler.cs
@@ -16,11 +16,39 @@ public class GetHistoryMessagesHandler(BotContext bot, EntityConvert convert) :
     public async Task<GetHistoryMessagesResult> HandleAsync(GetHistoryMessagesParameter parameter, CancellationToken token)
     {
         int start;
-        if (parameter.StartMessageSeq.HasValue) start = (int)(parameter.StartMessageSeq.Value - parameter.Limit);
-        // TODO: No start sequence
-        else throw new NotImplementedException();
+        int end;
 
-        int end = start + parameter.Limit;
+        if (parameter.StartMessageSeq.HasValue)
+        {
+            start = (int)(parameter.StartMessageSeq.Value - parameter.Limit);
+            end = (int)parameter.StartMessageSeq.Value;
+        }
+        else
+        {
+            // No start sequence provided, try to get the latest sequence
+            switch (parameter.MessageScene)
+            {
+                case "group":
+                    var groups = await _bot.FetchGroups();
+                    var group = groups.FirstOrDefault(g => g.GroupUin == parameter.PeerId)
+                        ?? throw new ApiException(-1, $"Group {parameter.PeerId} not found");
+                    
+                    if (group.LastestSeq == 0)
+                        throw new ApiException(-1, $"Failed to get latest sequence for group {parameter.PeerId}");
+                    
+                    end = (int)group.LastestSeq;
+                    start = end - parameter.Limit;
+                    break;
+                    
+                case "friend":
+                    throw new ApiException(-1, "Getting latest messages for friends without start_message_seq is not supported");
+                    
+                default:
+                    throw new NotSupportedException($"Message scene '{parameter.MessageScene}' is not supported");
+            }
+        }
+
+        if (start < 0) start = 0;
 
         var messages = parameter.MessageScene switch
         {
diff --git a/Lagrange.Proto.Test/CrashTest.cs b/Lagrange.Proto.Test/CrashTest.cs
new file mode 100644
index 00000000..6b4c37f8
--- /dev/null
+++ b/Lagrange.Proto.Test/CrashTest.cs
@@ -0,0 +1,45 @@
+using NUnit.Framework;
+using Lagrange.Proto.Utility;
+
+namespace Lagrange.Proto.Test
+{
+    [TestFixture]
+    public class CrashTest
+    {
+        [Test]
+        public void TestNegativeInt32VarIntLength()
+        {
+            // This test is used to reproduce the IndexOutOfRangeException Bug
+            int value = -1;
+            
+            int length = ProtoHelper.GetVarIntLength(value);
+            
+            // Verify: For a 32-bit all-ones number (0xFFFF), VarInt encoding should be 5 bytes
+            Assert.That(length, Is.EqualTo(5));
+        }
+
+        [Test]
+        public void TestNegativeInt64VarIntLength()
+        {
+            long value = -1;
+            
+            // For 64-bit numbers with all 1s, VarInt encoding should be 10 bytes
+            int length = ProtoHelper.GetVarIntLength(value);
+            
+            Assert.That(length, Is.EqualTo(10));
+        }
+        
+        [Test]
+        public void TestOtherNegativeValues()
+        {
+             // Test other negative values to ensure stability
+             int val1 = -100;
+             int len1 = ProtoHelper.GetVarIntLength(val1);
+             Assert.That(len1, Is.GreaterThan(0));
+
+             long val2 = long.MinValue; // 0x8000000000000000
+             int len2 = ProtoHelper.GetVarIntLength(val2);
+             Assert.That(len2, Is.EqualTo(10));
+        }
+    }
+}
\ No newline at end of file
diff --git a/Lagrange.Proto/Primitives/ProtoWriter.cs b/Lagrange.Proto/Primitives/ProtoWriter.cs
index 55b5da29..a59946b2 100644
--- a/Lagrange.Proto/Primitives/ProtoWriter.cs
+++ b/Lagrange.Proto/Primitives/ProtoWriter.cs
@@ -96,7 +96,8 @@ public void EncodeVarInt<T>(T value) where T : unmanaged, INumber<T>
     {
         if (_memory.Length - BytesPending >= 10)
         {
-            if (value < T.CreateTruncating(0x80))
+            // For-1 (int), converting to ulong is 0xFF... FF, much greater than 0x80, will not mistakenly enter this branch.
+            if (ulong.CreateTruncating(value) < 0x80)
             {
                 Unsafe.Add(ref MemoryMarshal.GetReference(_memory.Span), BytesPending++) = byte.CreateTruncating(value);
                 return;
diff --git a/Lagrange.Proto/Utility/ProtoHelper.cs b/Lagrange.Proto/Utility/ProtoHelper.cs
index 01517c05..399db314 100644
--- a/Lagrange.Proto/Utility/ProtoHelper.cs
+++ b/Lagrange.Proto/Utility/ProtoHelper.cs
@@ -36,12 +36,12 @@ public static unsafe int GetVarIntLength<T>(T value) where T : unmanaged, INumbe
         
         if (sizeof(T) <= 4)
         {
-            int leadingZeros = BitOperations.LeadingZeroCount(uint.CreateSaturating(value));
+            int leadingZeros = BitOperations.LeadingZeroCount(uint.CreateTruncating(value));
             return VarIntLengths32[leadingZeros];
         }
         else
         {
-            int leadingZeros = BitOperations.LeadingZeroCount(ulong.CreateSaturating(value));
+            int leadingZeros = BitOperations.LeadingZeroCount(ulong.CreateTruncating(value));
             return VarIntLengths64[leadingZeros];
         }
     }
@@ -98,4 +98,4 @@ public static int CountBytes(ReadOnlySpan<byte> str)
     {
         return GetVarIntLength(str.Length) + str.Length;
     }
-}
\ No newline at end of file
+}