feat(im-service): add friend system and conversations endpoint

- Add im_friends table with bi-directional add/remove (FriendController)
- Add GET /api/im/conversations: returns per-conversation latest message summaries
  using UNION of SINGLE/GROUP queries with correct peer ID computation
- Add ConversationSummary projection interface in ImMessageRepository

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

im-service/src/main/java/com/xuqm/im/controller/ConversationController.java

@@ -0,0 +1,33 @@
+package com.xuqm.im.controller;
+
+import com.xuqm.common.model.ApiResponse;
+import com.xuqm.im.repository.ImMessageRepository;
+import com.xuqm.im.service.MessageService;
+import org.springframework.http.ResponseEntity;
+import org.springframework.security.core.annotation.AuthenticationPrincipal;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RequestParam;
+import org.springframework.web.bind.annotation.RestController;
+
+import java.util.List;
+
+@RestController
+@RequestMapping("/api/im")
+public class ConversationController {
+
+    private final MessageService messageService;
+
+    public ConversationController(MessageService messageService) {
+        this.messageService = messageService;
+    }
+
+    @GetMapping("/conversations")
+    public ResponseEntity<ApiResponse<List<ImMessageRepository.ConversationSummary>>> conversations(
+            @AuthenticationPrincipal String userId,
+            @RequestParam String appId,
+            @RequestParam(defaultValue = "0") int page,
+            @RequestParam(defaultValue = "20") int size) {
+        return ResponseEntity.ok(ApiResponse.success(messageService.conversations(appId, userId, size)));
+    }
+}

im-service/src/main/java/com/xuqm/im/controller/FriendController.java

@@ -0,0 +1,78 @@
+package com.xuqm.im.controller;
+
+import com.xuqm.common.model.ApiResponse;
+import com.xuqm.im.entity.ImFriendEntity;
+import com.xuqm.im.repository.ImFriendRepository;
+import org.springframework.http.ResponseEntity;
+import org.springframework.security.core.annotation.AuthenticationPrincipal;
+import org.springframework.web.bind.annotation.DeleteMapping;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.PathVariable;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RequestParam;
+import org.springframework.web.bind.annotation.RestController;
+
+import java.util.List;
+
+@RestController
+@RequestMapping("/api/im/friends")
+public class FriendController {
+
+    private final ImFriendRepository friendRepository;
+
+    public FriendController(ImFriendRepository friendRepository) {
+        this.friendRepository = friendRepository;
+    }
+
+    @GetMapping
+    public ResponseEntity<ApiResponse<List<String>>> listFriends(
+            @AuthenticationPrincipal String userId,
+            @RequestParam String appId) {
+        List<String> friendIds = friendRepository.findByAppIdAndUserId(appId, userId)
+                .stream()
+                .map(ImFriendEntity::getFriendId)
+                .toList();
+        return ResponseEntity.ok(ApiResponse.success(friendIds));
+    }
+
+    @PostMapping
+    public ResponseEntity<ApiResponse<ImFriendEntity>> addFriend(
+            @AuthenticationPrincipal String userId,
+            @RequestParam String appId,
+            @RequestParam String friendId) {
+        // Insert userId -> friendId if not already present
+        ImFriendEntity forward = friendRepository
+                .findByAppIdAndUserIdAndFriendId(appId, userId, friendId)
+                .orElseGet(() -> {
+                    ImFriendEntity e = new ImFriendEntity();
+                    e.setAppId(appId);
+                    e.setUserId(userId);
+                    e.setFriendId(friendId);
+                    return friendRepository.save(e);
+                });
+
+        // Insert friendId -> userId bi-directionally if not already present
+        friendRepository.findByAppIdAndUserIdAndFriendId(appId, friendId, userId)
+                .orElseGet(() -> {
+                    ImFriendEntity e = new ImFriendEntity();
+                    e.setAppId(appId);
+                    e.setUserId(friendId);
+                    e.setFriendId(userId);
+                    return friendRepository.save(e);
+                });
+
+        return ResponseEntity.ok(ApiResponse.success(forward));
+    }
+
+    @DeleteMapping("/{friendId}")
+    public ResponseEntity<ApiResponse<Void>> removeFriend(
+            @AuthenticationPrincipal String userId,
+            @PathVariable String friendId,
+            @RequestParam String appId) {
+        // Remove both directions
+        friendRepository.deleteByAppIdAndUserIdAndFriendId(appId, userId, friendId);
+        friendRepository.deleteByAppIdAndUserIdAndFriendId(appId, friendId, userId);
+        return ResponseEntity.ok(ApiResponse.success(null));
+    }
+}

im-service/src/main/java/com/xuqm/im/entity/ImFriendEntity.java

@@ -0,0 +1,50 @@
+package com.xuqm.im.entity;
+
+import jakarta.persistence.Column;
+import jakarta.persistence.Entity;
+import jakarta.persistence.GeneratedValue;
+import jakarta.persistence.GenerationType;
+import jakarta.persistence.Id;
+import jakarta.persistence.Table;
+import jakarta.persistence.UniqueConstraint;
+import org.hibernate.annotations.CreationTimestamp;
+
+import java.time.Instant;
+
+@Entity
+@Table(name = "im_friends",
+       uniqueConstraints = @UniqueConstraint(columnNames = {"appId", "userId", "friendId"}))
+public class ImFriendEntity {
+
+    @Id
+    @GeneratedValue(strategy = GenerationType.IDENTITY)
+    private Long id;
+
+    @Column(nullable = false, length = 64)
+    private String appId;
+
+    @Column(nullable = false, length = 128)
+    private String userId;
+
+    @Column(nullable = false, length = 128)
+    private String friendId;
+
+    @CreationTimestamp
+    @Column(nullable = false, updatable = false)
+    private Instant createdAt;
+
+    public Long getId() { return id; }
+    public void setId(Long id) { this.id = id; }
+
+    public String getAppId() { return appId; }
+    public void setAppId(String appId) { this.appId = appId; }
+
+    public String getUserId() { return userId; }
+    public void setUserId(String userId) { this.userId = userId; }
+
+    public String getFriendId() { return friendId; }
+    public void setFriendId(String friendId) { this.friendId = friendId; }
+
+    public Instant getCreatedAt() { return createdAt; }
+    public void setCreatedAt(Instant createdAt) { this.createdAt = createdAt; }
+}

im-service/src/main/java/com/xuqm/im/repository/ImFriendRepository.java

@@ -0,0 +1,18 @@
+package com.xuqm.im.repository;
+
+import com.xuqm.im.entity.ImFriendEntity;
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.transaction.annotation.Transactional;
+
+import java.util.List;
+import java.util.Optional;
+
+public interface ImFriendRepository extends JpaRepository<ImFriendEntity, Long> {
+
+    List<ImFriendEntity> findByAppIdAndUserId(String appId, String userId);
+
+    Optional<ImFriendEntity> findByAppIdAndUserIdAndFriendId(String appId, String userId, String friendId);
+
+    @Transactional
+    void deleteByAppIdAndUserIdAndFriendId(String appId, String userId, String friendId);
+}

im-service/src/main/java/com/xuqm/im/repository/ImMessageRepository.java

@@ -7,8 +7,44 @@ import org.springframework.data.jpa.repository.JpaRepository;
 import org.springframework.data.jpa.repository.Query;
 import org.springframework.data.repository.query.Param;
 import java.time.LocalDateTime;
+import java.util.List;
 
 public interface ImMessageRepository extends JpaRepository<ImMessageEntity, String> {
+
+    interface ConversationSummary {
+        String getTargetId();
+        String getChatType();
+        LocalDateTime getLastTime();
+    }
+
+    @Query(value = """
+            SELECT target_id AS targetId, chat_type AS chatType, last_time AS lastTime
+            FROM (
+              SELECT
+                CASE WHEN from_user_id = :userId THEN to_id ELSE from_user_id END AS target_id,
+                chat_type,
+                MAX(created_at) AS last_time
+              FROM im_message
+              WHERE app_id = :appId AND chat_type = 'SINGLE'
+                AND (from_user_id = :userId OR to_id = :userId)
+              GROUP BY target_id, chat_type
+              UNION ALL
+              SELECT to_id AS target_id, chat_type, MAX(created_at) AS last_time
+              FROM im_message
+              WHERE app_id = :appId AND chat_type = 'GROUP'
+                AND to_id IN (
+                  SELECT id FROM im_group
+                  WHERE app_id = :appId AND FIND_IN_SET(:userId, member_ids) > 0
+                )
+              GROUP BY to_id, chat_type
+            ) combined
+            ORDER BY last_time DESC
+            LIMIT :size
+            """, nativeQuery = true)
+    List<ConversationSummary> findConversations(
+            @Param("appId") String appId,
+            @Param("userId") String userId,
+            @Param("size") int size);
     Page<ImMessageEntity> findByAppIdAndToIdOrderByCreatedAtDesc(
             String appId, String toId, Pageable pageable);
     Page<ImMessageEntity> findByAppIdAndFromUserIdAndToIdOrderByCreatedAtDesc(

im-service/src/main/java/com/xuqm/im/service/MessageService.java

@@ -6,7 +6,6 @@ import com.xuqm.im.cluster.ImClusterPublisher;
 import com.xuqm.im.entity.ImMessageEntity;
 import com.xuqm.im.entity.WebhookConfigEntity;
 import com.xuqm.im.model.SendMessageRequest;
-import com.xuqm.im.repository.ImMessageRepository;
 import com.xuqm.im.repository.WebhookConfigRepository;
 import org.springframework.beans.factory.annotation.Value;
 import org.springframework.data.domain.Page;
@@ -19,6 +18,7 @@ import java.net.http.HttpClient;
 import java.net.http.HttpRequest;
 import java.net.http.HttpResponse;
 import java.time.LocalDateTime;
+import com.xuqm.im.repository.ImMessageRepository;
 import java.util.List;
 import java.util.UUID;
 
@@ -109,6 +109,10 @@ public class MessageService {
                 appId, userId, toId, PageRequest.of(page, size));
     }
 
+    public List<ImMessageRepository.ConversationSummary> conversations(String appId, String userId, int size) {
+        return messageRepository.findConversations(appId, userId, size);
+    }
+
     @Async
     protected void dispatchWebhooks(String appId, ImMessageEntity message) {
         List<WebhookConfigEntity> webhooks = webhookRepository.findByAppIdAndEnabledTrue(appId);