diff --git a/docs/superpowers/plans/2026-07-24-buildflow-architecture-and-sop.md b/docs/superpowers/plans/2026-07-24-buildflow-architecture-and-sop.md
index 4ad322a..7160e03 100644
--- a/docs/superpowers/plans/2026-07-24-buildflow-architecture-and-sop.md
+++ b/docs/superpowers/plans/2026-07-24-buildflow-architecture-and-sop.md
@@ -227,11 +227,11 @@ git commit -m "refactor: stream rag answers through cqrs"
 - Replace: `tests/BuildFlow.IM.Integration.Tests/InMemoryUserInfoService.cs` with `InMemoryUserSummaryQueryHandler.cs`
 - Modify: `tests/BuildFlow.IM.Integration.Tests/ImServerFixture.cs`
 
-- [ ] **Step 1: Write Platform query tests and update IM tests to expect mediator sends**
+- [x] **Step 1: Write Platform query tests and update IM tests to expect mediator sends**
 
-The Platform query returns a `Dictionary<Guid, UserSummaryDto>` for distinct requested IDs and performs one database query. IM tests must configure `IMediator.Send(new GetUserSummariesQuery(...), ct)` and verify that empty input avoids a send where practical.
+The Platform query returns an `IReadOnlyDictionary<Guid, UserSummaryDto>` for distinct requested IDs and performs one database query. IM tests must configure `IMediator.Send(new GetUserSummariesQuery(...), ct)` and verify that empty input avoids a send where practical.
 
-- [ ] **Step 2: Run focused tests to verify RED**
+- [x] **Step 2: Run focused tests to verify RED**
 
 ```bash
 dotnet test tests/BuildFlow.Platform.Tests/BuildFlow.Platform.Tests.csproj --no-restore --filter FullyQualifiedName~GetUserSummaries
@@ -240,17 +240,17 @@ dotnet test tests/BuildFlow.IM.Tests/BuildFlow.IM.Tests.csproj --no-restore --fi
 
 Expected: FAIL until the target-owned query and IM handler changes exist.
 
-- [ ] **Step 3: Implement the direct CQRS calls**
+- [x] **Step 3: Implement the direct CQRS calls**
 
 Add a Platform Application project reference to IM Application. Each IM handler injects `IMediator`, sends one `GetUserSummariesQuery` for its deduplicated IDs, and reads results by `Guid` key. Do not catch all exceptions and do not introduce a replacement service/interface bridge.
 
-The integration fake implements `IRequestHandler<GetUserSummariesQuery, Dictionary<Guid, UserSummaryDto>>`; `ImServerFixture` registers both the IM Application assembly and the test assembly with MediatR.
+The integration fake implements `IRequestHandler<GetUserSummariesQuery, IReadOnlyDictionary<Guid, UserSummaryDto>>`; `ImServerFixture` registers both the IM Application assembly and the test assembly with MediatR.
 
-- [ ] **Step 4: Remove bridge interface, Host implementation, and registration**
+- [x] **Step 4: Remove bridge interface, Host implementation, and registration**
 
 Delete `IUserInfoService` and `InProcessUserInfoService`; remove the Host `AddScoped<IUserInfoService, InProcessUserInfoService>()` registration and stale using directives/comments.
 
-- [ ] **Step 5: Run IM unit and SignalR integration tests**
+- [x] **Step 5: Run IM unit and SignalR integration tests**
 
 ```bash
 dotnet test tests/BuildFlow.IM.Tests/BuildFlow.IM.Tests.csproj --no-restore
@@ -259,7 +259,7 @@ dotnet test tests/BuildFlow.IM.Integration.Tests/BuildFlow.IM.Integration.Tests.
 
 Expected: PASS with the same private/group conversation display names and notification behavior.
 
-- [ ] **Step 6: Commit**
+- [x] **Step 6: Commit**
 
 ```bash
 git add src/modules/platform/Application/Users src/modules/im src/BuildFlow.Host tests/BuildFlow.IM.Tests tests/BuildFlow.IM.Integration.Tests
diff --git a/src/BuildFlow.Host/BuildFlowHostModule.cs b/src/BuildFlow.Host/BuildFlowHostModule.cs
index 29348d7..4253485 100644
--- a/src/BuildFlow.Host/BuildFlowHostModule.cs
+++ b/src/BuildFlow.Host/BuildFlowHostModule.cs
@@ -91,7 +91,6 @@ public class BuildFlowHostModule : AbpModule
         // 当前用户上下文：各模块的 CurrentUserContext 实现
         services.AddHttpContextAccessor();
         services.AddScoped<BuildFlow.Shared.Domain.Common.ICurrentUserContext, CurrentUserContext>();
-        services.AddScoped<IUserInfoService, InProcessUserInfoService>();
 
         // 串联：IM @AI → RAG 问答（跨模块集成，RAG 实现 IAiBotHandler 供 IM 调用）
         services
diff --git a/src/BuildFlow.Host/Services/Integration/InProcessUserInfoService.cs b/src/BuildFlow.Host/Services/Integration/InProcessUserInfoService.cs
deleted file mode 100644
index 7ee3c37..0000000
--- a/src/BuildFlow.Host/Services/Integration/InProcessUserInfoService.cs
+++ /dev/null
@@ -1,41 +0,0 @@
-using MediatR;
-using BuildFlow.Platform.Application.Users.Queries;
-using IM.Domain.Common;
-
-namespace BuildFlow.Host.Services.Integration;
-
-/// <summary>
-/// 进程内用户信息查询实现，替代 IM 原有的 gRPC 版 <c>AuthGrpcClientService</c>。
-/// 通过 MediatR 查询调用 rag 模块的 <see cref="GetUserNamesQuery"/> 处理器，
-/// 而非直接注入 <c>PlatformDbContext</c>——这样 im 模块对 rag 的依赖从「直接引用 DbContext」
-/// 降级为「发 MediatR 消息」，实现模块间解耦。im 只依赖消息契约，不感知 rag 的数据访问实现。
-///
-/// 容错策略与 gRPC 版一致：查询失败返回空字典，避免 IM 核心链路因数据库抖动而整体不可用。
-/// 注册为 <c>IUserInfoService</c> 的覆盖实现（后注册者胜出），让 BuildFlow Host 内的 IM 直接查询用户信息。
-/// </summary>
-public class InProcessUserInfoService(IMediator mediator) : IUserInfoService
-{
-    public async Task<Dictionary<string, (string Username, string? Avatar)>> GetUsersAsync(
-        IEnumerable<Guid> userIds, CancellationToken ct = default)
-    {
-        var idList = userIds.ToList();
-        if (idList.Count == 0)
-            return [];
-
-        try
-        {
-            // 通过 MediatR 查询调用 rag 模块的 GetUserNamesQueryHandler（它内部查 PlatformDbContext.Users）
-            var names = await mediator.Send(new GetUserNamesQuery(idList), ct);
-
-            // rag 的 User 无 Avatar 字段（gRPC 服务端也返回 Avatar=""），故头像恒为 null
-            return names.ToDictionary(
-                kv => kv.Key.ToString(),
-                kv => (kv.Value, (string?)null));
-        }
-        catch
-        {
-            // 数据库不可用时降级返回空，保证消息发送主链路不被阻断（与 gRPC 版容错一致）
-            return [];
-        }
-    }
-}
diff --git a/src/modules/im/Application/Chat/Handlers/CreatePrivateConversationCommandHandler.cs b/src/modules/im/Application/Chat/Handlers/CreatePrivateConversationCommandHandler.cs
index 96e3d63..d7a1ae5 100644
--- a/src/modules/im/Application/Chat/Handlers/CreatePrivateConversationCommandHandler.cs
+++ b/src/modules/im/Application/Chat/Handlers/CreatePrivateConversationCommandHandler.cs
@@ -1,6 +1,6 @@
+using BuildFlow.Platform.Application.Users.Queries;
 using IM.Application.Chat.Commands;
 using IM.Application.Chat.DTOs;
-using IM.Domain.Common;
 using IM.Domain.Entities.Conversation;
 using IM.Domain.Entities.ConversationParticipant;
 using IM.Domain.Enums;
@@ -14,7 +14,7 @@ namespace IM.Application.Chat.Handlers;
 /// </summary>
 public class CreatePrivateConversationCommandHandler(
     ImDbContext db,
-    IUserInfoService userInfoService)
+    IMediator mediator)
     : IRequestHandler<CreatePrivateConversationCommand, ConversationDto>
 {
     public async Task<ConversationDto> Handle(
@@ -39,8 +39,8 @@ public class CreatePrivateConversationCommandHandler(
             })
             .FirstOrDefaultAsync(ct);
 
-        var users = await userInfoService.GetUsersAsync([request.TargetUserId], ct);
-        var targetUser = users.GetValueOrDefault(request.TargetUserId.ToString());
+        var users = await mediator.Send(new GetUserSummariesQuery([request.TargetUserId]), ct);
+        var targetUser = users.GetValueOrDefault(request.TargetUserId);
 
         if (existing is not null)
         {
@@ -52,8 +52,8 @@ public class CreatePrivateConversationCommandHandler(
                 existing.MyUnread,
                 null, null, null,
                 request.TargetUserId,
-                targetUser.Username,
-                targetUser.Avatar);
+                targetUser?.Username,
+                targetUser?.Avatar);
         }
 
         // 创建新私聊会话
@@ -88,7 +88,7 @@ public class CreatePrivateConversationCommandHandler(
             null, null, 0,
             null, null, null,
             request.TargetUserId,
-            targetUser.Username,
-            targetUser.Avatar);
+            targetUser?.Username,
+            targetUser?.Avatar);
     }
 }
diff --git a/src/modules/im/Application/Chat/Handlers/GetConversationsQueryHandler.cs b/src/modules/im/Application/Chat/Handlers/GetConversationsQueryHandler.cs
index 93ab7a0..ee8d047 100644
--- a/src/modules/im/Application/Chat/Handlers/GetConversationsQueryHandler.cs
+++ b/src/modules/im/Application/Chat/Handlers/GetConversationsQueryHandler.cs
@@ -1,3 +1,5 @@
+using BuildFlow.Platform.Application.Users.DTOs;
+using BuildFlow.Platform.Application.Users.Queries;
 using IM.Application.Chat.DTOs;
 using IM.Application.Chat.Queries;
 using IM.Domain.Common;
@@ -11,7 +13,7 @@ namespace IM.Application.Chat.Handlers;
 /// </summary>
 public class GetConversationsQueryHandler(
     ImDbContext db,
-    IUserInfoService userInfoService,
+    IMediator mediator,
     IUnreadCounter unreadCounter)
     : IRequestHandler<GetConversationsQuery, List<ConversationDto>>
 {
@@ -31,7 +33,7 @@ public class GetConversationsQueryHandler(
             .ThenByDescending(p => p.ConversationEntity.LastMessageAt)
             .ToListAsync(ct);
 
-        // 私聊会话需解析"对方"用户以展示头像/昵称；批量收集去重后一次性查 gRPC，避免逐会话往返
+        // 私聊会话需解析"对方"用户以展示头像/昵称；批量收集去重后一次性查询 Platform，避免逐会话往返。
         var otherUserIds = participants
             .Where(p => p.ConversationEntity.Type == Domain.Enums.ConversationTypeEnum.Private)
             .Select(p => p.ConversationEntity.Participants
@@ -42,8 +44,8 @@ public class GetConversationsQueryHandler(
             .ToList();
 
         var users = otherUserIds.Count > 0
-            ? await userInfoService.GetUsersAsync(otherUserIds, ct)
-            : new Dictionary<string, (string Username, string? Avatar)>();
+            ? await mediator.Send(new GetUserSummariesQuery(otherUserIds), ct)
+            : new Dictionary<Guid, UserSummaryDto>();
 
         var redisUnread = await unreadCounter.GetByUserAsync(
             request.UserId,
@@ -63,9 +65,9 @@ public class GetConversationsQueryHandler(
                 if (otherParticipant is not null)
                 {
                     otherUserId = otherParticipant.UserId;
-                    var userInfo = users.GetValueOrDefault(otherParticipant.UserId.ToString());
-                    otherUserName = userInfo.Username;
-                    otherUserAvatar = userInfo.Avatar;
+                    var userInfo = users.GetValueOrDefault(otherParticipant.UserId);
+                    otherUserName = userInfo?.Username;
+                    otherUserAvatar = userInfo?.Avatar;
                 }
             }
 
diff --git a/src/modules/im/Application/Chat/Handlers/GetGroupMembersQueryHandler.cs b/src/modules/im/Application/Chat/Handlers/GetGroupMembersQueryHandler.cs
index 7522977..7bd2863 100644
--- a/src/modules/im/Application/Chat/Handlers/GetGroupMembersQueryHandler.cs
+++ b/src/modules/im/Application/Chat/Handlers/GetGroupMembersQueryHandler.cs
@@ -1,7 +1,8 @@
+using BuildFlow.Platform.Application.Users.DTOs;
+using BuildFlow.Platform.Application.Users.Queries;
 using BuildFlow.Shared.Domain.Exceptions;
 using IM.Application.Chat.DTOs;
 using IM.Application.Chat.Queries;
-using IM.Domain.Common;
 using IM.Infrastructure.Persistence;
 using MediatR;
 
@@ -10,7 +11,7 @@ namespace IM.Application.Chat.Handlers;
 /// <summary>
 /// 群成员列表查询处理器。校验请求者群成员身份后返回成员。
 /// </summary>
-public class GetGroupMembersQueryHandler(ImDbContext db, IUserInfoService userInfoService) : IRequestHandler<GetGroupMembersQuery, List<GroupMemberDto>>
+public class GetGroupMembersQueryHandler(ImDbContext db, IMediator mediator) : IRequestHandler<GetGroupMembersQuery, List<GroupMemberDto>>
 {
     public async Task<List<GroupMemberDto>> Handle(GetGroupMembersQuery request, CancellationToken ct)
     {
@@ -25,14 +26,16 @@ public class GetGroupMembersQueryHandler(ImDbContext db, IUserInfoService userIn
             .Where(m => m.GroupId == request.GroupId)
             .ToListAsync(ct);
 
-        // 批量反查用户名/头像，避免逐成员调用 gRPC
-        var userIds = members.Select(m => m.UserId).ToList();
-        var users = await userInfoService.GetUsersAsync(userIds, ct);
+        // 批量反查用户名/头像，避免逐成员跨模块查询。
+        var userIds = members.Select(m => m.UserId).Distinct().ToList();
+        var users = userIds.Count > 0
+            ? await mediator.Send(new GetUserSummariesQuery(userIds), ct)
+            : new Dictionary<Guid, UserSummaryDto>();
 
         return members.Select(m =>
         {
-            var userInfo = users.GetValueOrDefault(m.UserId.ToString());
-            return new GroupMemberDto(m.UserId, userInfo.Username ?? string.Empty, userInfo.Avatar, m.Role, m.JoinedAt);
+            var userInfo = users.GetValueOrDefault(m.UserId);
+            return new GroupMemberDto(m.UserId, userInfo?.Username ?? string.Empty, userInfo?.Avatar, m.Role, m.JoinedAt);
         }).ToList();
     }
 }
diff --git a/src/modules/im/Application/Chat/Handlers/GetMessageHistoryQueryHandler.cs b/src/modules/im/Application/Chat/Handlers/GetMessageHistoryQueryHandler.cs
index ca2646d..5ad3219 100644
--- a/src/modules/im/Application/Chat/Handlers/GetMessageHistoryQueryHandler.cs
+++ b/src/modules/im/Application/Chat/Handlers/GetMessageHistoryQueryHandler.cs
@@ -1,7 +1,8 @@
+using BuildFlow.Platform.Application.Users.DTOs;
+using BuildFlow.Platform.Application.Users.Queries;
 using BuildFlow.Shared.Domain.Exceptions;
 using IM.Application.Chat.DTOs;
 using IM.Application.Chat.Queries;
-using IM.Domain.Common;
 using IM.Infrastructure.Mongo;
 using IM.Infrastructure.Persistence;
 using MediatR;
@@ -14,7 +15,7 @@ namespace IM.Application.Chat.Handlers;
 /// </summary>
 public class GetMessageHistoryQueryHandler(
     ImDbContext db,
-    IUserInfoService userInfoService) : IRequestHandler<GetMessageHistoryQuery, MessageHistoryDto>
+    IMediator mediator) : IRequestHandler<GetMessageHistoryQuery, MessageHistoryDto>
 {
     public async Task<MessageHistoryDto> Handle(GetMessageHistoryQuery request, CancellationToken ct)
     {
@@ -44,7 +45,7 @@ public class GetMessageHistoryQueryHandler(
         if (hasMore)
             messages.RemoveAt(messages.Count - 1);
 
-        // 头像懒补全：仅对消息文档中头像字段为空的发送者批量反查 gRPC，减少调用次数
+        // 头像懒补全：仅对消息文档中头像字段为空的发送者批量查询 Platform，减少调用次数。
         var senderIds = messages
             .Where(m => string.IsNullOrEmpty(m.SenderAvatar))
             .Select(m => m.SenderId)
@@ -52,15 +53,15 @@ public class GetMessageHistoryQueryHandler(
             .ToList();
 
         var users = senderIds.Count > 0
-            ? await userInfoService.GetUsersAsync(senderIds, ct)
-            : new Dictionary<string, (string Username, string? Avatar)>();
+            ? await mediator.Send(new GetUserSummariesQuery(senderIds), ct)
+            : new Dictionary<Guid, UserSummaryDto>();
 
         var dtos = messages.Select(m =>
         {
             var avatar = m.SenderAvatar;
             if (string.IsNullOrEmpty(avatar))
             {
-                avatar = users.GetValueOrDefault(m.SenderId.ToString()).Avatar;
+                avatar = users.GetValueOrDefault(m.SenderId)?.Avatar;
             }
 
             return new MessageDto(
diff --git a/src/modules/im/Application/Chat/Handlers/GetMessagesAroundQueryHandler.cs b/src/modules/im/Application/Chat/Handlers/GetMessagesAroundQueryHandler.cs
index f9c3431..f1a3c54 100644
--- a/src/modules/im/Application/Chat/Handlers/GetMessagesAroundQueryHandler.cs
+++ b/src/modules/im/Application/Chat/Handlers/GetMessagesAroundQueryHandler.cs
@@ -1,7 +1,8 @@
+using BuildFlow.Platform.Application.Users.DTOs;
+using BuildFlow.Platform.Application.Users.Queries;
 using BuildFlow.Shared.Domain.Exceptions;
 using IM.Application.Chat.DTOs;
 using IM.Application.Chat.Queries;
-using IM.Domain.Common;
 using IM.Infrastructure.Mongo;
 using IM.Infrastructure.Persistence;
 using MediatR;
@@ -14,7 +15,7 @@ namespace IM.Application.Chat.Handlers;
 /// </summary>
 public class GetMessagesAroundQueryHandler(
     ImDbContext db,
-    IUserInfoService userInfoService) : IRequestHandler<GetMessagesAroundQuery, MessageHistoryDto>
+    IMediator mediator) : IRequestHandler<GetMessagesAroundQuery, MessageHistoryDto>
 {
     public async Task<MessageHistoryDto> Handle(GetMessagesAroundQuery request, CancellationToken ct)
     {
@@ -98,15 +99,15 @@ public class GetMessagesAroundQueryHandler(
             .ToList();
 
         var users = senderIds.Count > 0
-            ? await userInfoService.GetUsersAsync(senderIds, ct)
-            : new Dictionary<string, (string Username, string? Avatar)>();
+            ? await mediator.Send(new GetUserSummariesQuery(senderIds), ct)
+            : new Dictionary<Guid, UserSummaryDto>();
 
         return messages.Select(m =>
         {
             var avatar = m.SenderAvatar;
             if (string.IsNullOrEmpty(avatar))
             {
-                avatar = users.GetValueOrDefault(m.SenderId.ToString()).Avatar;
+                avatar = users.GetValueOrDefault(m.SenderId)?.Avatar;
             }
 
             return new MessageDto(
diff --git a/src/modules/im/Application/Chat/Handlers/SearchMessagesQueryHandler.cs b/src/modules/im/Application/Chat/Handlers/SearchMessagesQueryHandler.cs
index 9725561..9d35e2a 100644
--- a/src/modules/im/Application/Chat/Handlers/SearchMessagesQueryHandler.cs
+++ b/src/modules/im/Application/Chat/Handlers/SearchMessagesQueryHandler.cs
@@ -1,8 +1,9 @@
 using System.Text.RegularExpressions;
+using BuildFlow.Platform.Application.Users.DTOs;
+using BuildFlow.Platform.Application.Users.Queries;
 using BuildFlow.Shared.Domain.Exceptions;
 using IM.Application.Chat.DTOs;
 using IM.Application.Chat.Queries;
-using IM.Domain.Common;
 using IM.Infrastructure.Mongo;
 using IM.Infrastructure.Persistence;
 using MediatR;
@@ -16,7 +17,7 @@ namespace IM.Application.Chat.Handlers;
 /// </summary>
 public class SearchMessagesQueryHandler(
     ImDbContext db,
-    IUserInfoService userInfoService) : IRequestHandler<SearchMessagesQuery, MessageHistoryDto>
+    IMediator mediator) : IRequestHandler<SearchMessagesQuery, MessageHistoryDto>
 {
     public async Task<MessageHistoryDto> Handle(SearchMessagesQuery request, CancellationToken ct)
     {
@@ -61,15 +62,15 @@ public class SearchMessagesQueryHandler(
             .ToList();
 
         var users = senderIds.Count > 0
-            ? await userInfoService.GetUsersAsync(senderIds, ct)
-            : new Dictionary<string, (string Username, string? Avatar)>();
+            ? await mediator.Send(new GetUserSummariesQuery(senderIds), ct)
+            : new Dictionary<Guid, UserSummaryDto>();
 
         return messages.Select(m =>
         {
             var avatar = m.SenderAvatar;
             if (string.IsNullOrEmpty(avatar))
             {
-                avatar = users.GetValueOrDefault(m.SenderId.ToString()).Avatar;
+                avatar = users.GetValueOrDefault(m.SenderId)?.Avatar;
             }
 
             return new MessageDto(
diff --git a/src/modules/im/Application/Chat/Handlers/SendMessageCommandHandler.cs b/src/modules/im/Application/Chat/Handlers/SendMessageCommandHandler.cs
index fae661f..a9e965f 100644
--- a/src/modules/im/Application/Chat/Handlers/SendMessageCommandHandler.cs
+++ b/src/modules/im/Application/Chat/Handlers/SendMessageCommandHandler.cs
@@ -1,3 +1,4 @@
+using BuildFlow.Platform.Application.Users.Queries;
 using BuildFlow.Shared.Domain.Exceptions;
 using BuildFlow.Shared.Integration;
 using IM.Application.Chat.Commands;
@@ -17,7 +18,7 @@ namespace IM.Application.Chat.Handlers;
 /// </summary>
 public class SendMessageCommandHandler(
     ImDbContext db,
-    IUserInfoService userInfoService,
+    IMediator mediator,
     IUnreadCounter unreadCounter,
     IOnlinePresenceService onlinePresence,
     IImNotificationPublisher notificationPublisher,
@@ -40,9 +41,9 @@ public class SendMessageCommandHandler(
         if (!isParticipant)
             throw new BusinessException(ErrorCode.Business, "您不是该会话的参与者");
 
-        // 通过 gRPC 向 rag-backend 反查发送者头像，与消息一并冗余落库，避免历史消息渲染时再查
-        var users = await userInfoService.GetUsersAsync([request.SenderId], ct);
-        var senderAvatar = users.GetValueOrDefault(request.SenderId.ToString()).Avatar;
+        // 批量查询 Platform 用户摘要，并把发送者头像冗余落库，避免历史消息渲染时重复查询。
+        var users = await mediator.Send(new GetUserSummariesQuery([request.SenderId]), ct);
+        var senderAvatar = users.GetValueOrDefault(request.SenderId)?.Avatar;
 
         var message = new MessageDocument
         {
diff --git a/src/modules/im/Application/IM.Application.csproj b/src/modules/im/Application/IM.Application.csproj
index f34c735..72752b1 100644
--- a/src/modules/im/Application/IM.Application.csproj
+++ b/src/modules/im/Application/IM.Application.csproj
@@ -13,5 +13,6 @@
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\Infrastructure\IM.Infrastructure.csproj" />
+    <ProjectReference Include="..\..\platform\Application\Platform.Application.csproj" />
   </ItemGroup>
 </Project>
diff --git a/src/modules/im/Domain/Common/IUserInfoService.cs b/src/modules/im/Domain/Common/IUserInfoService.cs
deleted file mode 100644
index 888affb..0000000
--- a/src/modules/im/Domain/Common/IUserInfoService.cs
+++ /dev/null
@@ -1,9 +0,0 @@
-namespace IM.Domain.Common;
-
-/// <summary>
-/// 用户信息查询抽象。供 IM 模块批量拉取用户展示名/头像，避免直接依赖外部账号服务。
-/// </summary>
-public interface IUserInfoService
-{
-    Task<Dictionary<string, (string Username, string? Avatar)>> GetUsersAsync(IEnumerable<Guid> userIds, CancellationToken ct = default);
-}
diff --git a/src/modules/platform/Application/Users/DTOs/UserSummaryDto.cs b/src/modules/platform/Application/Users/DTOs/UserSummaryDto.cs
new file mode 100644
index 0000000..5272a0c
--- /dev/null
+++ b/src/modules/platform/Application/Users/DTOs/UserSummaryDto.cs
@@ -0,0 +1,9 @@
+namespace BuildFlow.Platform.Application.Users.DTOs;
+
+/// <summary>
+/// 用户摘要 DTO。供其他模块批量读取用户展示名和头像引用。
+/// </summary>
+public sealed record UserSummaryDto(
+    Guid Id,
+    string Username,
+    string? Avatar);
diff --git a/src/modules/platform/Application/Users/Handlers/GetUserSummariesQueryHandler.cs b/src/modules/platform/Application/Users/Handlers/GetUserSummariesQueryHandler.cs
new file mode 100644
index 0000000..ec93270
--- /dev/null
+++ b/src/modules/platform/Application/Users/Handlers/GetUserSummariesQueryHandler.cs
@@ -0,0 +1,31 @@
+using BuildFlow.Platform.Application.Users.DTOs;
+using BuildFlow.Platform.Application.Users.Queries;
+using BuildFlow.Platform.Infrastructure.Persistence;
+using MediatR;
+
+namespace BuildFlow.Platform.Application.Users.Handlers;
+
+/// <summary>
+/// 批量用户摘要查询处理器。单次数据库查询返回去重后的现存用户。
+/// </summary>
+public sealed class GetUserSummariesQueryHandler(PlatformDbContext db)
+    : IRequestHandler<GetUserSummariesQuery, IReadOnlyDictionary<Guid, UserSummaryDto>>
+{
+    public async Task<IReadOnlyDictionary<Guid, UserSummaryDto>> Handle(
+        GetUserSummariesQuery request,
+        CancellationToken ct)
+    {
+        var userIds = request.UserIds.Distinct().ToArray();
+        if (userIds.Length == 0)
+        {
+            return new Dictionary<Guid, UserSummaryDto>();
+        }
+
+        return await db.Users
+            .Where(user => userIds.Contains(user.Id))
+            .ToDictionaryAsync(
+                user => user.Id,
+                user => new UserSummaryDto(user.Id, user.Username, user.Avatar),
+                ct);
+    }
+}
diff --git a/src/modules/platform/Application/Users/Queries/GetUserSummariesQuery.cs b/src/modules/platform/Application/Users/Queries/GetUserSummariesQuery.cs
new file mode 100644
index 0000000..20932c2
--- /dev/null
+++ b/src/modules/platform/Application/Users/Queries/GetUserSummariesQuery.cs
@@ -0,0 +1,10 @@
+using BuildFlow.Platform.Application.Users.DTOs;
+using MediatR;
+
+namespace BuildFlow.Platform.Application.Users.Queries;
+
+/// <summary>
+/// 批量用户摘要查询。按用户 ID 返回展示名和头像引用。
+/// </summary>
+public sealed record GetUserSummariesQuery(IReadOnlyCollection<Guid> UserIds)
+    : IRequest<IReadOnlyDictionary<Guid, UserSummaryDto>>;
diff --git a/tests/BuildFlow.IM.Integration.Tests/ChatHubAuthAndHistoryTests.cs b/tests/BuildFlow.IM.Integration.Tests/ChatHubAuthAndHistoryTests.cs
index 944bb26..9e3435e 100644
--- a/tests/BuildFlow.IM.Integration.Tests/ChatHubAuthAndHistoryTests.cs
+++ b/tests/BuildFlow.IM.Integration.Tests/ChatHubAuthAndHistoryTests.cs
@@ -44,8 +44,8 @@ public class ChatHubAuthAndHistoryTests : IAsyncLifetime
     public async Task Non_participant_cannot_join_conversation_group()
     {
         // Arrange：Alice 与 Bob 的私聊，Outsider 不参与
-        _fixture.UserInfoService.SetUser(ImServerFixture.AliceId, "Alice");
-        _fixture.UserInfoService.SetUser(ImServerFixture.BobId, "Bob");
+        _fixture.UserSummaryHandler.SetUser(ImServerFixture.AliceId, "Alice");
+        _fixture.UserSummaryHandler.SetUser(ImServerFixture.BobId, "Bob");
         var convId = await ImTestSeeder.SeedPrivateConversationAsync(_fixture, ImServerFixture.AliceId, ImServerFixture.BobId);
 
         var outsider = await ConnectAsync(ImServerFixture.OutSiderId, "Outsider");
@@ -89,7 +89,7 @@ public class ChatHubAuthAndHistoryTests : IAsyncLifetime
     public async Task Message_history_cursor_pagination_returns_correct_page_and_hasmore()
     {
         // Arrange：直接落多条消息到 MongoDB（绕过 Hub，聚焦分页逻辑）
-        _fixture.UserInfoService.SetUser(ImServerFixture.AliceId, "Alice");
+        _fixture.UserSummaryHandler.SetUser(ImServerFixture.AliceId, "Alice");
         var convId = await ImTestSeeder.SeedPrivateConversationAsync(_fixture, ImServerFixture.AliceId, ImServerFixture.BobId);
 
         var messageIds = await SeedMessagesAsync(convId, count: 5);
@@ -118,8 +118,8 @@ public class ChatHubAuthAndHistoryTests : IAsyncLifetime
     public async Task Search_messages_finds_text_sender_and_file_name_with_reply_metadata()
     {
         // Arrange：同一会话内准备正文、发送者、文件名三类命中；另一个会话放同关键字验证会话隔离。
-        _fixture.UserInfoService.SetUser(ImServerFixture.AliceId, "Alice");
-        _fixture.UserInfoService.SetUser(ImServerFixture.BobId, "BuildFlow Bob");
+        _fixture.UserSummaryHandler.SetUser(ImServerFixture.AliceId, "Alice");
+        _fixture.UserSummaryHandler.SetUser(ImServerFixture.BobId, "BuildFlow Bob");
         var convId = await ImTestSeeder.SeedPrivateConversationAsync(_fixture, ImServerFixture.AliceId, ImServerFixture.BobId);
         var otherConvId = await ImTestSeeder.SeedPrivateConversationAsync(_fixture, ImServerFixture.AliceId, ImServerFixture.CarolId);
 
@@ -170,7 +170,7 @@ public class ChatHubAuthAndHistoryTests : IAsyncLifetime
     public async Task Get_messages_around_returns_ordered_context_window()
     {
         // Arrange：写 5 条连续历史，定位第 3 条，要求返回前后各 1 条并按时间正序。
-        _fixture.UserInfoService.SetUser(ImServerFixture.AliceId, "Alice");
+        _fixture.UserSummaryHandler.SetUser(ImServerFixture.AliceId, "Alice");
         var convId = await ImTestSeeder.SeedPrivateConversationAsync(_fixture, ImServerFixture.AliceId, ImServerFixture.BobId);
         var messageIds = await SeedMessagesAsync(convId, count: 5);
 
@@ -193,7 +193,7 @@ public class ChatHubAuthAndHistoryTests : IAsyncLifetime
     public async Task Get_messages_around_includes_referenced_message_outside_context_window()
     {
         // Arrange：目标消息引用了更早的消息，但该引用消息不在前后 1 条上下文窗口内。
-        _fixture.UserInfoService.SetUser(ImServerFixture.AliceId, "Alice");
+        _fixture.UserSummaryHandler.SetUser(ImServerFixture.AliceId, "Alice");
         var convId = await ImTestSeeder.SeedPrivateConversationAsync(_fixture, ImServerFixture.AliceId, ImServerFixture.BobId);
         var baseTime = DateTime.UtcNow.AddMinutes(-4);
 
diff --git a/tests/BuildFlow.IM.Integration.Tests/ChatHubLifecycleTests.cs b/tests/BuildFlow.IM.Integration.Tests/ChatHubLifecycleTests.cs
index 7ceac50..95977c1 100644
--- a/tests/BuildFlow.IM.Integration.Tests/ChatHubLifecycleTests.cs
+++ b/tests/BuildFlow.IM.Integration.Tests/ChatHubLifecycleTests.cs
@@ -97,8 +97,8 @@ public class ChatHubLifecycleTests : IAsyncLifetime
     public async Task Connection_auto_subscribes_user_to_all_existing_conversations()
     {
         // Arrange：先播种一个会话，随后让参与者连接——验证"连接即订阅"
-        _fixture.UserInfoService.SetUser(ImServerFixture.AliceId, "Alice");
-        _fixture.UserInfoService.SetUser(ImServerFixture.BobId, "Bob");
+        _fixture.UserSummaryHandler.SetUser(ImServerFixture.AliceId, "Alice");
+        _fixture.UserSummaryHandler.SetUser(ImServerFixture.BobId, "Bob");
         var convId = await ImTestSeeder.SeedPrivateConversationAsync(_fixture, ImServerFixture.AliceId, ImServerFixture.BobId);
 
         var bob = await ConnectAsync(ImServerFixture.BobId, "Bob");
diff --git a/tests/BuildFlow.IM.Integration.Tests/ChatHubMessagingTests.cs b/tests/BuildFlow.IM.Integration.Tests/ChatHubMessagingTests.cs
index e7dac45..8420b34 100644
--- a/tests/BuildFlow.IM.Integration.Tests/ChatHubMessagingTests.cs
+++ b/tests/BuildFlow.IM.Integration.Tests/ChatHubMessagingTests.cs
@@ -45,8 +45,8 @@ public class ChatHubMessagingTests : IAsyncLifetime
     public async Task SendMessage_broadcasts_to_both_participants_and_persists_to_mongo()
     {
         // Arrange：私聊会话 Alice ↔ Bob，两者均在连接中
-        _fixture.UserInfoService.SetUser(ImServerFixture.AliceId, "Alice");
-        _fixture.UserInfoService.SetUser(ImServerFixture.BobId, "Bob");
+        _fixture.UserSummaryHandler.SetUser(ImServerFixture.AliceId, "Alice");
+        _fixture.UserSummaryHandler.SetUser(ImServerFixture.BobId, "Bob");
         var convId = await ImTestSeeder.SeedPrivateConversationAsync(_fixture, ImServerFixture.AliceId, ImServerFixture.BobId);
 
         var alice = await ConnectAsync(ImServerFixture.AliceId, "Alice");
@@ -94,8 +94,8 @@ public class ChatHubMessagingTests : IAsyncLifetime
     public async Task SendMessage_file_message_preserves_metadata_reply_and_updates_conversation_summary()
     {
         // Arrange：前端文件发送链路会先完成分片上传，再通过 ChatHub 发送文件名、大小和预览 URL。
-        _fixture.UserInfoService.SetUser(ImServerFixture.AliceId, "Alice");
-        _fixture.UserInfoService.SetUser(ImServerFixture.BobId, "Bob");
+        _fixture.UserSummaryHandler.SetUser(ImServerFixture.AliceId, "Alice");
+        _fixture.UserSummaryHandler.SetUser(ImServerFixture.BobId, "Bob");
         var convId = await ImTestSeeder.SeedPrivateConversationAsync(
             _fixture,
             ImServerFixture.AliceId,
@@ -167,7 +167,7 @@ public class ChatHubMessagingTests : IAsyncLifetime
     public async Task SendMessage_increments_redis_unread_for_other_participant_only()
     {
         // Arrange：Alice、Bob、Carol 三人群聊。发消息时只给除发送者外的两人累加未读
-        _fixture.UserInfoService.SetUser(ImServerFixture.AliceId, "Alice");
+        _fixture.UserSummaryHandler.SetUser(ImServerFixture.AliceId, "Alice");
         var (convId, _) = await ImTestSeeder.SeedGroupConversationAsync(
             _fixture, "三人测试群", ImServerFixture.AliceId,
             (ImServerFixture.AliceId, GroupMemberRoleEnum.Owner),
@@ -197,7 +197,7 @@ public class ChatHubMessagingTests : IAsyncLifetime
     public async Task SendMessage_triggers_offline_notification_for_offline_recipients()
     {
         // Arrange：Bob 离线（不连接）、Carol 在线（连接）。离线触达仅应发给 Bob
-        _fixture.UserInfoService.SetUser(ImServerFixture.AliceId, "Alice");
+        _fixture.UserSummaryHandler.SetUser(ImServerFixture.AliceId, "Alice");
         var (convId, _) = await ImTestSeeder.SeedGroupConversationAsync(
             _fixture, "离线通知群", ImServerFixture.AliceId,
             (ImServerFixture.AliceId, GroupMemberRoleEnum.Owner),
@@ -231,8 +231,8 @@ public class ChatHubMessagingTests : IAsyncLifetime
     public async Task Typing_broadcasts_OnUserTyping_to_participants()
     {
         // Arrange
-        _fixture.UserInfoService.SetUser(ImServerFixture.AliceId, "Alice");
-        _fixture.UserInfoService.SetUser(ImServerFixture.BobId, "Bob");
+        _fixture.UserSummaryHandler.SetUser(ImServerFixture.AliceId, "Alice");
+        _fixture.UserSummaryHandler.SetUser(ImServerFixture.BobId, "Bob");
         var convId = await ImTestSeeder.SeedPrivateConversationAsync(_fixture, ImServerFixture.AliceId, ImServerFixture.BobId);
 
         var alice = await ConnectAsync(ImServerFixture.AliceId, "Alice");
diff --git a/tests/BuildFlow.IM.Integration.Tests/ChatHubReadAndRecallTests.cs b/tests/BuildFlow.IM.Integration.Tests/ChatHubReadAndRecallTests.cs
index 3490ed5..472ca48 100644
--- a/tests/BuildFlow.IM.Integration.Tests/ChatHubReadAndRecallTests.cs
+++ b/tests/BuildFlow.IM.Integration.Tests/ChatHubReadAndRecallTests.cs
@@ -45,8 +45,8 @@ public class ChatHubReadAndRecallTests : IAsyncLifetime
     public async Task MarkAsRead_resets_unread_in_both_pg_and_redis_and_broadcasts()
     {
         // Arrange：私聊会话，Alice 先发消息使 Bob 产生未读
-        _fixture.UserInfoService.SetUser(ImServerFixture.AliceId, "Alice");
-        _fixture.UserInfoService.SetUser(ImServerFixture.BobId, "Bob");
+        _fixture.UserSummaryHandler.SetUser(ImServerFixture.AliceId, "Alice");
+        _fixture.UserSummaryHandler.SetUser(ImServerFixture.BobId, "Bob");
         var convId = await ImTestSeeder.SeedPrivateConversationAsync(_fixture, ImServerFixture.AliceId, ImServerFixture.BobId);
 
         var alice = await ConnectAsync(ImServerFixture.AliceId, "Alice");
@@ -94,7 +94,7 @@ public class ChatHubReadAndRecallTests : IAsyncLifetime
     public async Task RecallMessage_marks_mongo_recalled_and_updates_conversation_summary()
     {
         // Arrange：私聊会话，Alice 发一条消息（成为最后一条），随后本人撤回
-        _fixture.UserInfoService.SetUser(ImServerFixture.AliceId, "Alice");
+        _fixture.UserSummaryHandler.SetUser(ImServerFixture.AliceId, "Alice");
         var convId = await ImTestSeeder.SeedPrivateConversationAsync(_fixture, ImServerFixture.AliceId, ImServerFixture.BobId);
 
         var alice = await ConnectAsync(ImServerFixture.AliceId, "Alice");
diff --git a/tests/BuildFlow.IM.Integration.Tests/ImServerFixture.cs b/tests/BuildFlow.IM.Integration.Tests/ImServerFixture.cs
index 747915d..1767734 100644
--- a/tests/BuildFlow.IM.Integration.Tests/ImServerFixture.cs
+++ b/tests/BuildFlow.IM.Integration.Tests/ImServerFixture.cs
@@ -11,8 +11,11 @@ using Microsoft.Extensions.DependencyInjection.Extensions;
 using Microsoft.IdentityModel.JsonWebTokens;
 using Microsoft.IdentityModel.Tokens;
 using FluentValidation;
+using MediatR;
 using MongoDB.Driver;
 using MongoDB.Entities;
+using BuildFlow.Platform.Application.Users.DTOs;
+using BuildFlow.Platform.Application.Users.Queries;
 using BuildFlow.Shared.Domain.Common;
 using BuildFlow.Shared.Infrastructure;
 using IM.Application.Chat.Commands;
@@ -25,7 +28,7 @@ namespace BuildFlow.IM.Integration.Tests;
 
 /// <summary>
 /// 集成测试夹具：在 TestServer 上装配真实 SignalR ChatHub + 真实 PostgreSQL / MongoDB / Redis，
-/// 仅替换两个外部 gRPC 依赖（用户信息、通知发布）为进程内 fake，使测试聚焦于"SignalR + DB"主链路。
+/// 仅替换用户摘要查询和通知发布为进程内 fake，使测试聚焦于"SignalR + DB"主链路。
 /// </summary>
 /// <remarks>
 /// 设计取舍：
@@ -70,8 +73,8 @@ public sealed class ImServerFixture : IAsyncLifetime
     /// <summary>外部通知发布的 fake：记录最后一次调用参数，便于断言离线触达。</summary>
     public FakeImNotificationPublisher NotificationPublisher { get; } = new();
 
-    /// <summary>外部用户信息查询的 fake：返回预设的用户名/头像。</summary>
-    public InMemoryUserInfoService UserInfoService { get; } = new();
+    /// <summary>Platform 用户摘要查询 fake：返回预设的用户名和头像。</summary>
+    public InMemoryUserSummaryQueryHandler UserSummaryHandler { get; } = new();
 
     public async Task InitializeAsync()
     {
@@ -104,13 +107,17 @@ public sealed class ImServerFixture : IAsyncLifetime
         services.AddSingleton<IOnlinePresenceService, RedisOnlinePresenceService>();
         services.AddSingleton<IUnreadCounter, RedisUnreadCounter>();
 
-        // —— 外部 gRPC 依赖替换为进程内 fake ——
-        services.AddSingleton<IUserInfoService>(UserInfoService);
+        // —— 外部通知依赖替换为进程内 fake ——
         services.AddSingleton<IImNotificationPublisher>(NotificationPublisher);
 
         // —— MediatR + 校验管线（与生产 Application 模块一致） ——
         var assembly = typeof(SendMessageCommand).Assembly;
-        services.AddMediatR(cfg => cfg.RegisterServicesFromAssembly(assembly));
+        services.AddMediatR(cfg => cfg
+            .RegisterServicesFromAssembly(assembly)
+            .RegisterServicesFromAssembly(typeof(InMemoryUserSummaryQueryHandler).Assembly));
+        services.RemoveAll<IRequestHandler<GetUserSummariesQuery, IReadOnlyDictionary<Guid, UserSummaryDto>>>();
+        services.AddSingleton<IRequestHandler<GetUserSummariesQuery, IReadOnlyDictionary<Guid, UserSummaryDto>>>(
+            UserSummaryHandler);
         services.AddValidatorsFromAssembly(typeof(SendMessageCommand).Assembly);
 
         services.AddSignalR(options =>
diff --git a/tests/BuildFlow.IM.Integration.Tests/InMemoryUserInfoService.cs b/tests/BuildFlow.IM.Integration.Tests/InMemoryUserInfoService.cs
deleted file mode 100644
index 5e6e652..0000000
--- a/tests/BuildFlow.IM.Integration.Tests/InMemoryUserInfoService.cs
+++ /dev/null
@@ -1,27 +0,0 @@
-using IM.Domain.Common;
-
-namespace BuildFlow.IM.Integration.Tests;
-
-/// <summary>
-/// 进程内 <see cref="IUserInfoService"/> 替身：避免真实 gRPC 调用到未运行的 SSO 服务。
-/// 测试前调用 <see cref="SetUser"/> 预置用户展示名/头像，Handler 调用时按 ID 返回。
-/// </summary>
-public sealed class InMemoryUserInfoService : IUserInfoService
-{
-    private readonly Dictionary<Guid, (string Username, string? Avatar)> _users = new();
-
-    public void SetUser(Guid userId, string username, string? avatar = null) =>
-        _users[userId] = (username, avatar);
-
-    public Task<Dictionary<string, (string Username, string? Avatar)>> GetUsersAsync(
-        IEnumerable<Guid> userIds, CancellationToken ct = default)
-    {
-        var result = new Dictionary<string, (string Username, string? Avatar)>();
-        foreach (var id in userIds)
-        {
-            if (_users.TryGetValue(id, out var info))
-                result[id.ToString()] = info;
-        }
-        return Task.FromResult(result);
-    }
-}
diff --git a/tests/BuildFlow.IM.Integration.Tests/InMemoryUserSummaryQueryHandler.cs b/tests/BuildFlow.IM.Integration.Tests/InMemoryUserSummaryQueryHandler.cs
new file mode 100644
index 0000000..93b8de4
--- /dev/null
+++ b/tests/BuildFlow.IM.Integration.Tests/InMemoryUserSummaryQueryHandler.cs
@@ -0,0 +1,32 @@
+using BuildFlow.Platform.Application.Users.DTOs;
+using BuildFlow.Platform.Application.Users.Queries;
+using MediatR;
+
+namespace BuildFlow.IM.Integration.Tests;
+
+/// <summary>
+/// 进程内用户摘要查询处理器。测试前可预置用户展示名和头像，由 MediatR 按用户 ID 批量返回。
+/// </summary>
+public sealed class InMemoryUserSummaryQueryHandler
+    : IRequestHandler<GetUserSummariesQuery, IReadOnlyDictionary<Guid, UserSummaryDto>>
+{
+    private readonly Dictionary<Guid, UserSummaryDto> _users = new();
+
+    /// <summary>
+    /// 预置一个用户摘要。
+    /// </summary>
+    public void SetUser(Guid userId, string username, string? avatar = null) =>
+        _users[userId] = new UserSummaryDto(userId, username, avatar);
+
+    public Task<IReadOnlyDictionary<Guid, UserSummaryDto>> Handle(
+        GetUserSummariesQuery request,
+        CancellationToken ct)
+    {
+        IReadOnlyDictionary<Guid, UserSummaryDto> result = request.UserIds
+            .Distinct()
+            .Where(_users.ContainsKey)
+            .ToDictionary(userId => userId, userId => _users[userId]);
+
+        return Task.FromResult(result);
+    }
+}
diff --git a/tests/BuildFlow.IM.Tests/Chat/GetConversationsQueryHandlerTests.cs b/tests/BuildFlow.IM.Tests/Chat/GetConversationsQueryHandlerTests.cs
index 904c2fe..882001c 100644
--- a/tests/BuildFlow.IM.Tests/Chat/GetConversationsQueryHandlerTests.cs
+++ b/tests/BuildFlow.IM.Tests/Chat/GetConversationsQueryHandlerTests.cs
@@ -1,8 +1,11 @@
+using BuildFlow.Platform.Application.Users.DTOs;
+using BuildFlow.Platform.Application.Users.Queries;
 using IM.Application.Chat.Handlers;
 using IM.Application.Chat.Queries;
 using IM.Domain.Common;
 using IM.Domain.Enums;
 using IM.Infrastructure.Persistence;
+using MediatR;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.DependencyInjection;
 using Moq;
@@ -30,14 +33,14 @@ public class GetConversationsQueryHandlerTests
             (OtherUserId, 0)));
         await db.SaveChangesAsync();
 
-        var userInfoService = new Mock<IUserInfoService>();
-        userInfoService
-            .Setup(s => s.GetUsersAsync(
-                It.Is<IEnumerable<Guid>>(ids => ids.SequenceEqual(new[] { OtherUserId })),
+        var mediator = new Mock<IMediator>();
+        mediator
+            .Setup(m => m.Send(
+                It.Is<GetUserSummariesQuery>(q => q.UserIds.SequenceEqual(new[] { OtherUserId })),
                 It.IsAny<CancellationToken>()))
-            .ReturnsAsync(new Dictionary<string, (string Username, string? Avatar)>
+            .ReturnsAsync(new Dictionary<Guid, UserSummaryDto>
             {
-                [OtherUserId.ToString()] = ("Bob", null)
+                [OtherUserId] = new(OtherUserId, "Bob", null)
             });
 
         var unreadCounter = new Mock<IUnreadCounter>();
@@ -48,12 +51,16 @@ public class GetConversationsQueryHandlerTests
                 It.IsAny<CancellationToken>()))
             .ReturnsAsync(new Dictionary<Guid, int> { [ConversationId] = 2 });
 
-        var handler = new GetConversationsQueryHandler(db, userInfoService.Object, unreadCounter.Object);
+        var handler = new GetConversationsQueryHandler(db, mediator.Object, unreadCounter.Object);
 
         var result = await handler.Handle(new GetConversationsQuery(UserId), CancellationToken.None);
 
         var conversation = Assert.Single(result);
         Assert.Equal(2, conversation.UnreadCount);
+        Assert.Equal("Bob", conversation.OtherUserName);
+        mediator.Verify(m => m.Send(
+            It.Is<GetUserSummariesQuery>(q => q.UserIds.SequenceEqual(new[] { OtherUserId })),
+            It.IsAny<CancellationToken>()), Times.Once);
     }
 
     private static ImDbContext BuildInMemoryDb()
diff --git a/tests/BuildFlow.IM.Tests/Chat/SendMessageCommandHandlerTests.cs b/tests/BuildFlow.IM.Tests/Chat/SendMessageCommandHandlerTests.cs
index a426aa4..968fb16 100644
--- a/tests/BuildFlow.IM.Tests/Chat/SendMessageCommandHandlerTests.cs
+++ b/tests/BuildFlow.IM.Tests/Chat/SendMessageCommandHandlerTests.cs
@@ -1,8 +1,11 @@
+using BuildFlow.Platform.Application.Users.DTOs;
+using BuildFlow.Platform.Application.Users.Queries;
 using IM.Application.Chat.Commands;
 using IM.Application.Chat.Handlers;
 using IM.Domain.Common;
 using IM.Domain.Enums;
 using IM.Infrastructure.Persistence;
+using MediatR;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.DependencyInjection;
 using MongoDB.Driver;
@@ -103,6 +106,34 @@ public class SendMessageCommandHandlerTests
         Assert.NotNull(conv.LastMessageAt);
     }
 
+    [Fact]
+    public async Task Queries_sender_summary_once_and_uses_returned_avatar()
+    {
+        await using var db = BuildInMemoryDb();
+        db.Conversations.Add(ImTestData.BuildConversation(ConversationId, ConversationTypeEnum.Private,
+            (SenderId, 0), (RecipientA, 0)));
+        await db.SaveChangesAsync();
+
+        var (handler, _, mediator, _, _) = BuildHandler(db);
+        mediator
+            .Setup(m => m.Send(
+                It.Is<GetUserSummariesQuery>(q => q.UserIds.SequenceEqual(new[] { SenderId })),
+                It.IsAny<CancellationToken>()))
+            .ReturnsAsync(new Dictionary<Guid, UserSummaryDto>
+            {
+                [SenderId] = new(SenderId, "alice", "avatars/alice.png")
+            });
+
+        var result = await handler.Handle(new SendMessageCommand(
+            ConversationId, SenderId, "alice",
+            MessageContentTypeEnum.Text, "hello", null, null), CancellationToken.None);
+
+        Assert.Equal("avatars/alice.png", result.SenderAvatar);
+        mediator.Verify(m => m.Send(
+            It.Is<GetUserSummariesQuery>(q => q.UserIds.SequenceEqual(new[] { SenderId })),
+            It.IsAny<CancellationToken>()), Times.Once);
+    }
+
     [Fact]
     public async Task Publishes_notification_to_offline_recipients_only()
     {
@@ -162,13 +193,13 @@ public class SendMessageCommandHandlerTests
     /// 构造 Handler。Mongo 消息正文落真实库（静态 DB.Default 已在静态构造函数初始化），
     /// 此处聚焦未读数语义。默认所有接收者视为离线（驱动通知链路），个别测试可覆盖。
     /// </summary>
-    private static (SendMessageCommandHandler Handler, Mock<IUnreadCounter> UnreadCounter, Mock<IUserInfoService> UserInfo, Mock<IOnlinePresenceService> OnlinePresence, Mock<IImNotificationPublisher> Notification) BuildHandler(ImDbContext db)
+    private static (SendMessageCommandHandler Handler, Mock<IUnreadCounter> UnreadCounter, Mock<IMediator> Mediator, Mock<IOnlinePresenceService> OnlinePresence, Mock<IImNotificationPublisher> Notification) BuildHandler(ImDbContext db)
     {
         var unreadCounter = new Mock<IUnreadCounter>();
 
-        var userInfo = new Mock<IUserInfoService>();
-        userInfo.Setup(u => u.GetUsersAsync(It.IsAny<IEnumerable<Guid>>(), It.IsAny<CancellationToken>()))
-                .ReturnsAsync(new Dictionary<string, (string, string?)>());
+        var mediator = new Mock<IMediator>();
+        mediator.Setup(m => m.Send(It.IsAny<GetUserSummariesQuery>(), It.IsAny<CancellationToken>()))
+                .ReturnsAsync(new Dictionary<Guid, UserSummaryDto>());
 
         // 默认全部离线（返回传入集合本身），驱动通知触发
         var onlinePresence = new Mock<IOnlinePresenceService>();
@@ -178,8 +209,8 @@ public class SendMessageCommandHandlerTests
         var notification = new Mock<IImNotificationPublisher>();
 
         var handler = new SendMessageCommandHandler(
-            db, userInfo.Object, unreadCounter.Object, onlinePresence.Object, notification.Object);
-        return (handler, unreadCounter, userInfo, onlinePresence, notification);
+            db, mediator.Object, unreadCounter.Object, onlinePresence.Object, notification.Object);
+        return (handler, unreadCounter, mediator, onlinePresence, notification);
     }
 
     private static ImDbContext BuildInMemoryDb()
diff --git a/tests/BuildFlow.Platform.Tests/Users/GetUserSummariesQueryHandlerTests.cs b/tests/BuildFlow.Platform.Tests/Users/GetUserSummariesQueryHandlerTests.cs
new file mode 100644
index 0000000..dc67f87
--- /dev/null
+++ b/tests/BuildFlow.Platform.Tests/Users/GetUserSummariesQueryHandlerTests.cs
@@ -0,0 +1,47 @@
+using BuildFlow.Platform.Application.Users.DTOs;
+using BuildFlow.Platform.Application.Users.Handlers;
+using BuildFlow.Platform.Application.Users.Queries;
+using Xunit;
+
+namespace BuildFlow.Platform.Tests.Users;
+
+/// <summary>
+/// 批量用户摘要查询测试。覆盖去重、缺失用户过滤、头像返回和空输入短路。
+/// </summary>
+public class GetUserSummariesQueryHandlerTests
+{
+    [Fact]
+    public async Task Handle_ShouldReturnDistinctExistingUsersByGuid()
+    {
+        await using var db = PlatformTestDb.CreateDbContext();
+        var aliceId = Guid.NewGuid();
+        var bobId = Guid.NewGuid();
+        var missingId = Guid.NewGuid();
+        var alice = await PlatformTestDb.SeedUserAsync(db, aliceId, "alice");
+        var bob = await PlatformTestDb.SeedUserAsync(db, bobId, "bob");
+        alice.Avatar = "avatars/alice.png";
+        bob.Avatar = null;
+        await db.SaveChangesAsync();
+        var handler = new GetUserSummariesQueryHandler(db);
+
+        var result = await handler.Handle(
+            new GetUserSummariesQuery([aliceId, bobId, aliceId, missingId]),
+            CancellationToken.None);
+
+        Assert.Equal(2, result.Count);
+        Assert.Equal(new UserSummaryDto(aliceId, "alice", "avatars/alice.png"), result[aliceId]);
+        Assert.Equal(new UserSummaryDto(bobId, "bob", null), result[bobId]);
+        Assert.False(result.ContainsKey(missingId));
+    }
+
+    [Fact]
+    public async Task Handle_EmptyIds_ShouldReturnEmptyResult()
+    {
+        await using var db = PlatformTestDb.CreateDbContext();
+        var handler = new GetUserSummariesQueryHandler(db);
+
+        var result = await handler.Handle(new GetUserSummariesQuery([]), CancellationToken.None);
+
+        Assert.Empty(result);
+    }
+}