diff --git a/src/modules/rag/Application/Chat/Handlers/DeleteConversationCommandHandler.cs b/src/modules/rag/Application/Chat/Handlers/DeleteConversationCommandHandler.cs
index 8cd8437..1b9f98a 100644
--- a/src/modules/rag/Application/Chat/Handlers/DeleteConversationCommandHandler.cs
+++ b/src/modules/rag/Application/Chat/Handlers/DeleteConversationCommandHandler.cs
@@ -1,5 +1,6 @@
 using MediatR;
 using BuildFlow.Shared.Domain.Exceptions;
+using BuildFlow.Shared.Domain.Common;
 using BuildFlow.Domain.Interfaces;
 using BuildFlow.Infrastructure.Persistence;
 using BuildFlow.Application.Chat.Commands;
@@ -9,12 +10,18 @@ namespace BuildFlow.Application.Chat.Handlers;
 /// <summary>
 /// Delete会话Command处理器。执行业务校验后持久化。
 /// </summary>
-public class DeleteConversationCommandHandler(RagDbContext db, IChatMessageCache cache)
+public class DeleteConversationCommandHandler(
+    RagDbContext db,
+    IChatMessageCache cache,
+    ICurrentUserContext userContext)
     : IRequestHandler<DeleteConversationCommand, Unit>
 {
     public async Task<Unit> Handle(DeleteConversationCommand request, CancellationToken ct)
     {
-        var conversation = await db.Conversations.FindAsync([request.Id], ct)
+        var userId = Guid.Parse(userContext.GetRequiredUserId());
+        var conversation = await db.Conversations.FirstOrDefaultAsync(
+                x => x.Id == request.Id && x.UserId == userId,
+                ct)
             ?? throw new NotFoundException(ErrorCode.NotFound, "会话不存在");
 
         db.Conversations.Remove(conversation);
diff --git a/src/modules/rag/Application/Chat/Handlers/GetConversationDetailQueryHandler.cs b/src/modules/rag/Application/Chat/Handlers/GetConversationDetailQueryHandler.cs
index 84f52d6..a9d67e0 100644
--- a/src/modules/rag/Application/Chat/Handlers/GetConversationDetailQueryHandler.cs
+++ b/src/modules/rag/Application/Chat/Handlers/GetConversationDetailQueryHandler.cs
@@ -1,6 +1,7 @@
 using MediatR;
 using BuildFlow.Application.Chat.DTOs;
 using BuildFlow.Shared.Domain.Exceptions;
+using BuildFlow.Shared.Domain.Common;
 using BuildFlow.Domain.Interfaces;
 using BuildFlow.Infrastructure.Persistence;
 using BuildFlow.Application.Chat.Queries;
@@ -10,12 +11,18 @@ namespace BuildFlow.Application.Chat.Handlers;
 /// <summary>
 /// Get会话Detail查询处理器。执行业务校验后持久化。
 /// </summary>
-public class GetConversationDetailQueryHandler(RagDbContext db, IChatMessageCache cache)
+public class GetConversationDetailQueryHandler(
+    RagDbContext db,
+    IChatMessageCache cache,
+    ICurrentUserContext userContext)
     : IRequestHandler<GetConversationDetailQuery, ConversationDetailDto>
 {
     public async Task<ConversationDetailDto> Handle(GetConversationDetailQuery request, CancellationToken ct)
     {
-        var conversation = await db.Conversations.FindAsync([request.Id], ct)
+        var userId = Guid.Parse(userContext.GetRequiredUserId());
+        var conversation = await db.Conversations.FirstOrDefaultAsync(
+                x => x.Id == request.Id && x.UserId == userId,
+                ct)
             ?? throw new NotFoundException(ErrorCode.NotFound, "会话不存在");
 
         // 先查 Redis 缓存
diff --git a/src/modules/rag/Application/Chat/Handlers/SendMessageCommandHandler.cs b/src/modules/rag/Application/Chat/Handlers/SendMessageCommandHandler.cs
index e060b8e..35c22d5 100644
--- a/src/modules/rag/Application/Chat/Handlers/SendMessageCommandHandler.cs
+++ b/src/modules/rag/Application/Chat/Handlers/SendMessageCommandHandler.cs
@@ -3,6 +3,7 @@ using BuildFlow.Application.Chat.DTOs;
 using BuildFlow.Domain.Entities.ChatMessage;
 using BuildFlow.Domain.Enums;
 using BuildFlow.Shared.Domain.Exceptions;
+using BuildFlow.Shared.Domain.Common;
 using BuildFlow.Domain.Interfaces;
 using BuildFlow.Infrastructure.Persistence;
 using BuildFlow.Application.Chat.Commands;
@@ -12,28 +13,38 @@ using AiChatRole = Microsoft.Extensions.AI.ChatRole;
 
 namespace BuildFlow.Application.Chat.Handlers;
 
-public class SendMessageCommandHandler(RagDbContext db, IAIChatAgent chatAgent, IChatMessageCache cache)
+/// <summary>
+/// 向当前用户拥有的会话发送消息，并持久化用户消息和 AI 回复。
+/// </summary>
+public class SendMessageCommandHandler(
+    RagDbContext db,
+    IAIChatAgent chatAgent,
+    IChatMessageCache cache,
+    ICurrentUserContext userContext)
     : IRequestHandler<SendMessageCommand, SendMessageResponse>
 {
     public async Task<SendMessageResponse> Handle(SendMessageCommand request, CancellationToken ct)
     {
-        var conversation = await db.Conversations.FindAsync([request.ConversationId], ct)
+        var userId = Guid.Parse(userContext.GetRequiredUserId());
+        var conversation = await db.Conversations.FirstOrDefaultAsync(
+                x => x.Id == request.ConversationId && x.UserId == userId,
+                ct)
             ?? throw new NotFoundException(ErrorCode.NotFound, "会话不存在");
 
         var userMessage = new ChatMessageEntity
         {
-            ConversationId = request.ConversationId,
+            ConversationId = conversation.Id,
             Role = ChatRoleEnum.User,
             Content = request.Content
         };
         await db.ChatMessages.AddAsync(userMessage, ct);
         await db.SaveChangesAsync(ct);
 
-        await cache.AppendMessageAsync(request.ConversationId,
+        await cache.AppendMessageAsync(conversation.Id,
             new CachedChatMessage(userMessage.Id, ChatRoleEnum.User.ToString(), userMessage.Content, null, userMessage.CreatedAt), ct);
 
         var history = await db.ChatMessages
-            .Where(m => m.ConversationId == request.ConversationId)
+            .Where(m => m.ConversationId == conversation.Id)
             .OrderBy(m => m.CreatedAt)
             .ToListAsync(ct);
 
@@ -45,14 +56,14 @@ public class SendMessageCommandHandler(RagDbContext db, IAIChatAgent chatAgent,
 
         var assistantMessage = new ChatMessageEntity
         {
-            ConversationId = request.ConversationId,
+            ConversationId = conversation.Id,
             Role = ChatRoleEnum.Assistant,
             Content = reply
         };
         await db.ChatMessages.AddAsync(assistantMessage, ct);
         await db.SaveChangesAsync(ct);
 
-        await cache.AppendMessageAsync(request.ConversationId,
+        await cache.AppendMessageAsync(conversation.Id,
             new CachedChatMessage(assistantMessage.Id, ChatRoleEnum.Assistant.ToString(), assistantMessage.Content, null, assistantMessage.CreatedAt), ct);
 
         return new SendMessageResponse(assistantMessage.Id, reply);
diff --git a/src/modules/rag/Application/Chat/Handlers/UpdateConversationCommandHandler.cs b/src/modules/rag/Application/Chat/Handlers/UpdateConversationCommandHandler.cs
index 711343f..995be1f 100644
--- a/src/modules/rag/Application/Chat/Handlers/UpdateConversationCommandHandler.cs
+++ b/src/modules/rag/Application/Chat/Handlers/UpdateConversationCommandHandler.cs
@@ -1,19 +1,28 @@
 using BuildFlow.Application.Chat.Commands;
 using BuildFlow.Application.Chat.DTOs;
-using BuildFlow.Domain.Entities.Conversation;
 using BuildFlow.Infrastructure.Persistence;
+using BuildFlow.Shared.Domain.Common;
 using BuildFlow.Shared.Domain.Errors;
 using BuildFlow.Shared.Domain.Exceptions;
 using MediatR;
 
 namespace BuildFlow.Application.Chat.Handlers;
 
-public class UpdateConversationCommandHandler(RagDbContext db) : IRequestHandler<UpdateConversationCommand, ConversationDto>
+/// <summary>
+/// 更新当前用户拥有的 RAG 会话基本信息。
+/// </summary>
+public class UpdateConversationCommandHandler(
+    RagDbContext db,
+    ICurrentUserContext userContext)
+    : IRequestHandler<UpdateConversationCommand, ConversationDto>
 {
     public async Task<ConversationDto> Handle(UpdateConversationCommand request, CancellationToken ct)
     {
-        var conversation = await db.Conversations.FindAsync([request.Id], ct)
-            ?? throw new BusinessException(ErrorCode.NotFound, "会话不存在");
+        var userId = Guid.Parse(userContext.GetRequiredUserId());
+        var conversation = await db.Conversations.FirstOrDefaultAsync(
+                x => x.Id == request.Id && x.UserId == userId,
+                ct)
+            ?? throw new NotFoundException(ErrorCode.NotFound, "会话不存在");
         if (!string.IsNullOrWhiteSpace(request.Title))
             conversation.Title = request.Title;
         await db.SaveChangesAsync(ct);
diff --git a/tests/BuildFlow.Rag.Tests/ChatEndToEndTests.cs b/tests/BuildFlow.Rag.Tests/ChatEndToEndTests.cs
index bc6cdc5..216f96b 100644
--- a/tests/BuildFlow.Rag.Tests/ChatEndToEndTests.cs
+++ b/tests/BuildFlow.Rag.Tests/ChatEndToEndTests.cs
@@ -4,6 +4,7 @@ using BuildFlow.Domain.Entities.Conversation;
 using BuildFlow.Domain.Enums;
 using BuildFlow.Infrastructure.Persistence;
 using BuildFlow.Rag.Tests.Stub;
+using BuildFlow.Shared.Domain.Errors;
 using BuildFlow.Shared.Domain.Exceptions;
 using BuildFlow.Shared.Infrastructure;
 using FluentAssertions;
@@ -67,13 +68,14 @@ public class ChatEndToEndTests
     {
         // Given: 已创建会话 + 两轮对话
         await using var db = CreateDb("multi-turn");
-        var userId = Guid.Parse(new TestCurrentUserContext().UserId);
+        var userContext = new TestCurrentUserContext();
+        var userId = Guid.Parse(userContext.UserId);
         var conversationId = Guid.NewGuid();
         SeedConversation(db, conversationId, userId);
 
         var cache = new StubChatMessageCache();
         var chatAgent = new StubAIChatAgent { ReplyText = "你好！我是 AI 助手。" };
-        var handler = new SendMessageCommandHandler(db, chatAgent, cache);
+        var handler = new SendMessageCommandHandler(db, chatAgent, cache, userContext);
 
         // When: 第一轮
         var round1 = await handler.Handle(
@@ -113,7 +115,11 @@ public class ChatEndToEndTests
         await using var db = CreateDb("not-found");
         var cache = new StubChatMessageCache();
         var chatAgent = new StubAIChatAgent();
-        var handler = new SendMessageCommandHandler(db, chatAgent, cache);
+        var handler = new SendMessageCommandHandler(
+            db,
+            chatAgent,
+            cache,
+            new TestCurrentUserContext());
 
         // When/Then: 发消息到不存在的会话
         var act = async () => await handler.Handle(
@@ -123,6 +129,29 @@ public class ChatEndToEndTests
         await act.Should().ThrowAsync<NotFoundException>();
     }
 
+    [Fact]
+    public async Task SendMessage_OtherUsersConversation_ThrowsNotFoundWithoutWriting()
+    {
+        await using var db = CreateDb("send-other-user");
+        var userContext = new TestCurrentUserContext();
+        var conversationId = Guid.NewGuid();
+        SeedConversation(db, conversationId, Guid.NewGuid());
+        var cache = new StubChatMessageCache();
+        var handler = new SendMessageCommandHandler(
+            db,
+            new StubAIChatAgent(),
+            cache,
+            userContext);
+        var request = new SendMessageCommand(conversationId, "越权消息");
+
+        var act = () => handler.Handle(request, CancellationToken.None);
+
+        await act.Should().ThrowAsync<NotFoundException>()
+            .Where(x => x.Code == ErrorCode.NotFound && x.Message == "会话不存在");
+        db.ChatMessages.Should().BeEmpty();
+        cache.Count(conversationId).Should().Be(0);
+    }
+
     [Fact]
     public async Task CreateConversation_UnauthorizedUser_Throws()
     {
diff --git a/tests/BuildFlow.Rag.Tests/EmbeddingAndQueryTests.cs b/tests/BuildFlow.Rag.Tests/EmbeddingAndQueryTests.cs
index 41d8fcf..2f1a67e 100644
--- a/tests/BuildFlow.Rag.Tests/EmbeddingAndQueryTests.cs
+++ b/tests/BuildFlow.Rag.Tests/EmbeddingAndQueryTests.cs
@@ -12,6 +12,8 @@ using BuildFlow.Domain.Enums;
 using BuildFlow.Domain.Interfaces;
 using BuildFlow.Infrastructure.Persistence;
 using BuildFlow.Rag.Tests.Stub;
+using BuildFlow.Shared.Domain.Errors;
+using BuildFlow.Shared.Domain.Exceptions;
 using BuildFlow.Shared.Infrastructure;
 using FluentAssertions;
 using Microsoft.EntityFrameworkCore;
@@ -107,14 +109,15 @@ public class EmbeddingAndQueryTests
     {
         var db = CreateDb();
         var convId = Guid.NewGuid();
-        var userId = Guid.Parse(new TestCurrentUserContext().UserId);
+        var userContext = new TestCurrentUserContext();
+        var userId = Guid.Parse(userContext.UserId);
         db.Conversations.Add(new ConversationEntity { Id = convId, Title = "详情", UserId = userId });
         db.ChatMessages.Add(new ChatMessageEntity { ConversationId = convId, Role = ChatRoleEnum.User, Content = "你好" });
         db.ChatMessages.Add(new ChatMessageEntity { ConversationId = convId, Role = ChatRoleEnum.Assistant, Content = "回复" });
         await db.SaveChangesAsync();
 
         var cache = new StubChatMessageCache();
-        var handler = new GetConversationDetailQueryHandler(db, cache);
+        var handler = new GetConversationDetailQueryHandler(db, cache, userContext);
         var result = await handler.Handle(new GetConversationDetailQuery(convId), CancellationToken.None);
 
         result.Title.Should().Be("详情");
@@ -126,17 +129,93 @@ public class EmbeddingAndQueryTests
     {
         var db = CreateDb();
         var convId = Guid.NewGuid();
-        var userId = Guid.Parse(new TestCurrentUserContext().UserId);
+        var userContext = new TestCurrentUserContext();
+        var userId = Guid.Parse(userContext.UserId);
         db.Conversations.Add(new ConversationEntity { Id = convId, Title = "待删", UserId = userId });
         await db.SaveChangesAsync();
 
         var cache = new StubChatMessageCache();
         await cache.SetMessagesAsync(convId, [new CachedChatMessage(Guid.NewGuid(), "user", "hi", null, DateTime.UtcNow)]);
 
-        var handler = new DeleteConversationCommandHandler(db, cache);
+        var handler = new DeleteConversationCommandHandler(db, cache, userContext);
         await handler.Handle(new DeleteConversationCommand(convId), CancellationToken.None);
 
         (await db.Conversations.AnyAsync(c => c.Id == convId)).Should().BeFalse();
         cache.Count(convId).Should().Be(0, "cache 也应清除");
     }
+
+    [Fact]
+    public async Task GetConversationDetail_OtherUsersConversation_ThrowsNotFound()
+    {
+        await using var db = CreateDb();
+        var userContext = new TestCurrentUserContext();
+        var conversationId = Guid.NewGuid();
+        db.Conversations.Add(new ConversationEntity
+        {
+            Id = conversationId,
+            Title = "他人的详情",
+            UserId = Guid.NewGuid(),
+        });
+        await db.SaveChangesAsync();
+        var handler = new GetConversationDetailQueryHandler(
+            db,
+            new StubChatMessageCache(),
+            userContext);
+        var request = new GetConversationDetailQuery(conversationId);
+
+        var act = () => handler.Handle(request, CancellationToken.None);
+
+        await act.Should().ThrowAsync<NotFoundException>()
+            .Where(x => x.Code == ErrorCode.NotFound && x.Message == "会话不存在");
+    }
+
+    [Fact]
+    public async Task UpdateConversation_OtherUsersConversation_DoesNotChangeTitle()
+    {
+        await using var db = CreateDb();
+        var userContext = new TestCurrentUserContext();
+        var conversation = new ConversationEntity
+        {
+            Id = Guid.NewGuid(),
+            Title = "原始标题",
+            UserId = Guid.NewGuid(),
+        };
+        db.Conversations.Add(conversation);
+        await db.SaveChangesAsync();
+        var handler = new UpdateConversationCommandHandler(db, userContext);
+        var request = new UpdateConversationCommand(conversation.Id, "越权更新", null);
+
+        var act = () => handler.Handle(request, CancellationToken.None);
+
+        await act.Should().ThrowAsync<NotFoundException>()
+            .Where(x => x.Code == ErrorCode.NotFound && x.Message == "会话不存在");
+        conversation.Title.Should().Be("原始标题");
+    }
+
+    [Fact]
+    public async Task DeleteConversation_OtherUsersConversation_LeavesDbAndCacheUntouched()
+    {
+        await using var db = CreateDb();
+        var userContext = new TestCurrentUserContext();
+        var conversationId = Guid.NewGuid();
+        db.Conversations.Add(new ConversationEntity
+        {
+            Id = conversationId,
+            Title = "不可删除",
+            UserId = Guid.NewGuid(),
+        });
+        await db.SaveChangesAsync();
+        var cache = new StubChatMessageCache();
+        await cache.SetMessagesAsync(conversationId,
+            [new CachedChatMessage(Guid.NewGuid(), "user", "保留", null, DateTime.UtcNow)]);
+        var handler = new DeleteConversationCommandHandler(db, cache, userContext);
+        var request = new DeleteConversationCommand(conversationId);
+
+        var act = () => handler.Handle(request, CancellationToken.None);
+
+        await act.Should().ThrowAsync<NotFoundException>()
+            .Where(x => x.Code == ErrorCode.NotFound && x.Message == "会话不存在");
+        (await db.Conversations.AnyAsync(x => x.Id == conversationId)).Should().BeTrue();
+        cache.Count(conversationId).Should().Be(1);
+    }
 }