diff --git a/.cursor/skills/spark-im-v3/SKILL.md b/.cursor/skills/spark-im-v3/SKILL.md
index 193c051..5206660 100644
--- a/.cursor/skills/spark-im-v3/SKILL.md
+++ b/.cursor/skills/spark-im-v3/SKILL.md
@@ -58,13 +58,12 @@ Do **not** move `infrastructure` into `pkg` (or a public repo-root `pkg/`).
 
 ## IDs
 
-Not every PK is Snowflake. Do not AUTO_INCREMENT natural keys.
+Not every PK is Snowflake. Do not AUTO_INCREMENT Snowflake business ids (`users.id`, `messages.id`, `conversations.id`).
 
 | Kind | Examples | Rule |
 |------|----------|------|
 | Snowflake | `users.id` (uid), `messages.id` (MsgId), `conversations.id` | Time-ordered business IDs. One `id.Generator` per process; `snowflake_worker_id` unique per process. Clock rewind fails issuance for the whole process. |
-| AUTO_INCREMENT | `user_devices.id`, `groups.id` (群号), `friend_relations.id` | Internal row id, or sequential public 群号. Friend edges are directed (`user_id`→`friend_id`); UNIQUE `(user_id, friend_id)`. Business chat cursor is still Snowflake `conversations.id`. |
-| Natural key | `user_emails.email`, P2P `(user_small, user_big)`, members, sync cursors | Composite / natural PK. No extra surrogate id. |
+| AUTO_INCREMENT | `groups.id` (群号); row id on `user_devices`, `friend_relations`, `user_login_logs`, `user_emails`, `p2p_conversations`, `conversation_members`, `group_members`, `device_sync_cursors`, `message_deletes`, `moment_audience`, `moment_likes`, `moment_settings`, `moment_hides` | Table-local row id. Business uniqueness stays UNIQUE (email, P2P pair, members, cursors). Do not AUTO_INCREMENT Snowflake columns. |
 
 `device_id` is **client-generated**, stored on the device, written to JWT `did`. The server does not allocate it. `uid` in JSON **is** `users.id`; do not add a second uid column.
 
diff --git a/cmd/migrate/main.go b/cmd/migrate/main.go
index 5baacec..121d28b 100644
--- a/cmd/migrate/main.go
+++ b/cmd/migrate/main.go
@@ -128,6 +128,7 @@ func ignorableDDL(err error) bool {
 		1051, // unknown table
 		1060, // duplicate column
 		1061, // duplicate key name
+		1091, // can't drop; check that column/key exists
 		1146: // table doesn't exist
 		return true
 	default:
diff --git a/docs/architecture-v3.md b/docs/architecture-v3.md
index 182fda4..f578b90 100644
--- a/docs/architecture-v3.md
+++ b/docs/architecture-v3.md
@@ -441,20 +441,22 @@ CREATE TABLE conversations (
 
 -- 两人永远同一条会话，学 BFF 小 uid : 大 uid
 CREATE TABLE p2p_conversations (
+    id                BIGINT NOT NULL AUTO_INCREMENT PRIMARY KEY,
     user_small        BIGINT NOT NULL,
     user_big          BIGINT NOT NULL,
     conversation_id   BIGINT NOT NULL,
-    PRIMARY KEY (user_small, user_big),
+    UNIQUE KEY uk_p2p_users (user_small, user_big),
     UNIQUE KEY uk_conversation (conversation_id)
 );
 
 CREATE TABLE conversation_members (
+    id                  BIGINT NOT NULL AUTO_INCREMENT PRIMARY KEY,
     conversation_id     BIGINT NOT NULL,
     user_id             BIGINT NOT NULL,
     last_read_msg_id    BIGINT NOT NULL DEFAULT 0,
     joined_at           DATETIME(3) NOT NULL,
     muted               TINYINT NOT NULL DEFAULT 0,
-    PRIMARY KEY (conversation_id, user_id),
+    UNIQUE KEY uk_conversation_members (conversation_id, user_id),
     KEY idx_user_id (user_id)
 );
 ```
@@ -481,12 +483,13 @@ CREATE TABLE mailbox_events (
 );
 
 CREATE TABLE device_sync_cursors (
+    id               BIGINT NOT NULL AUTO_INCREMENT PRIMARY KEY,
     user_id          BIGINT NOT NULL,
     device_id        BIGINT NOT NULL,
     mailbox_seq      BIGINT NOT NULL DEFAULT 0,
     dialog_score     BIGINT NOT NULL DEFAULT 0,   -- Redis ZSET score 游标
     updated_at       DATETIME(3) NOT NULL,
-    PRIMARY KEY (user_id, device_id)
+    UNIQUE KEY uk_user_device (user_id, device_id)
 );
 ```
 
diff --git a/internal/module/conversation/model/conversation_member.go b/internal/module/conversation/model/conversation_member.go
index ae84452..ad0d414 100644
--- a/internal/module/conversation/model/conversation_member.go
+++ b/internal/module/conversation/model/conversation_member.go
@@ -10,8 +10,9 @@ import (
 
 // ConversationMember maps table conversation_members.
 type ConversationMember struct {
-	ConversationID int64     `gorm:"column:conversation_id;primaryKey;comment:会话 id"`
-	UserID         int64     `gorm:"column:user_id;primaryKey;comment:成员 user_id"`
+	ID             int64     `gorm:"column:id;primaryKey;autoIncrement;comment:行 id，表内自增，仅内部用；业务唯一键是 (conversation_id, user_id)"`
+	ConversationID int64     `gorm:"column:conversation_id;comment:会话 id"`
+	UserID         int64     `gorm:"column:user_id;comment:成员 user_id"`
 	LastReadMsgID  int64     `gorm:"column:last_read_msg_id;comment:该成员已读到的最大消息 id，未读真相；Redis 丢了可从此重建"`
 	JoinedAt       time.Time `gorm:"column:joined_at;comment:加入会话时间"`
 	Muted          int       `gorm:"column:muted;comment:0=未静音 1=免打扰"`
diff --git a/internal/module/conversation/model/p2p_conversation.go b/internal/module/conversation/model/p2p_conversation.go
index c377592..b8efb12 100644
--- a/internal/module/conversation/model/p2p_conversation.go
+++ b/internal/module/conversation/model/p2p_conversation.go
@@ -2,8 +2,9 @@ package model
 
 // P2PConversation maps table p2p_conversations.
 type P2PConversation struct {
-	UserSmall      int64 `gorm:"column:user_small;primaryKey;comment:两人中较小的 user_id，保证同一对用户只有一行"`
-	UserBig        int64 `gorm:"column:user_big;primaryKey;comment:两人中较大的 user_id"`
+	ID             int64 `gorm:"column:id;primaryKey;autoIncrement;comment:行 id，表内自增，仅内部用；业务唯一键是 (user_small, user_big)"`
+	UserSmall      int64 `gorm:"column:user_small;comment:两人中较小的 user_id，保证同一对用户只有一行"`
+	UserBig        int64 `gorm:"column:user_big;comment:两人中较大的 user_id"`
 	ConversationID int64 `gorm:"column:conversation_id;comment:对应 conversations.id"`
 }
 
diff --git a/internal/module/group/model/group_member.go b/internal/module/group/model/group_member.go
index 4a4a6d0..9141120 100644
--- a/internal/module/group/model/group_member.go
+++ b/internal/module/group/model/group_member.go
@@ -10,8 +10,9 @@ import (
 
 // GroupMember maps table group_members.
 type GroupMember struct {
-	GroupID    int64     `gorm:"column:group_id;primaryKey;comment:群号，groups.id"`
-	UserID     int64     `gorm:"column:user_id;primaryKey;comment:成员 user_id"`
+	ID         int64     `gorm:"column:id;primaryKey;autoIncrement;comment:行 id，表内自增，仅内部用；业务唯一键是 (group_id, user_id)"`
+	GroupID    int64     `gorm:"column:group_id;comment:群号，groups.id"`
+	UserID     int64     `gorm:"column:user_id;comment:成员 user_id"`
 	Role       int       `gorm:"column:role;comment:1=群主 2=管理员 3=普通成员"`
 	Nickname   string    `gorm:"column:nickname;comment:群内昵称，空则用用户昵称"`
 	Remark     string    `gorm:"column:remark;comment:成员对该群的备注，仅自己可见"`
diff --git a/internal/module/message/model/message_delete.go b/internal/module/message/model/message_delete.go
index a29376c..147262b 100644
--- a/internal/module/message/model/message_delete.go
+++ b/internal/module/message/model/message_delete.go
@@ -2,10 +2,11 @@ package model
 
 import "time"
 
-// MessageDelete maps table message_deletes. PK is (user_id, msg_id).
+// MessageDelete maps table message_deletes. Business unique key is (user_id, msg_id).
 type MessageDelete struct {
-	UserID         int64     `gorm:"column:user_id;primaryKey;comment:删除者 user_id，仅该用户历史不可见"`
-	MsgID          int64     `gorm:"column:msg_id;primaryKey;comment:被删除的 Snowflake MsgId"`
+	ID             int64     `gorm:"column:id;primaryKey;autoIncrement;comment:行 id，表内自增，仅内部用；业务唯一键是 (user_id, msg_id)"`
+	UserID         int64     `gorm:"column:user_id;comment:删除者 user_id，仅该用户历史不可见"`
+	MsgID          int64     `gorm:"column:msg_id;comment:被删除的 Snowflake MsgId"`
 	ConversationID int64     `gorm:"column:conversation_id;comment:所属会话，便于按会话过滤"`
 	CreatedAt      time.Time `gorm:"column:created_at;comment:删除时间"`
 }
diff --git a/internal/module/moment/model/row.go b/internal/module/moment/model/row.go
index fd59374..e93d704 100644
--- a/internal/module/moment/model/row.go
+++ b/internal/module/moment/model/row.go
@@ -56,16 +56,18 @@ func postFrom(p *entity.Post) *Post {
 
 // Audience maps table moment_audience.
 type Audience struct {
-	PostID int64 `gorm:"column:post_id;primaryKey;comment:帖 id"`
-	PeerID int64 `gorm:"column:peer_id;primaryKey;comment:白名单能看 / 黑名单不能看 的好友 uid"`
+	ID     int64 `gorm:"column:id;primaryKey;autoIncrement;comment:行 id，表内自增，仅内部用；业务唯一键是 (post_id, peer_id)"`
+	PostID int64 `gorm:"column:post_id;comment:帖 id"`
+	PeerID int64 `gorm:"column:peer_id;comment:白名单能看 / 黑名单不能看 的好友 uid"`
 }
 
 func (Audience) TableName() string { return "moment_audience" }
 
 // Like maps table moment_likes.
 type Like struct {
-	PostID    int64     `gorm:"column:post_id;primaryKey;comment:帖 id"`
-	UserID    int64     `gorm:"column:user_id;primaryKey;comment:点赞人"`
+	ID        int64     `gorm:"column:id;primaryKey;autoIncrement;comment:行 id，表内自增，仅内部用；业务唯一键是 (post_id, user_id)"`
+	PostID    int64     `gorm:"column:post_id;comment:帖 id"`
+	UserID    int64     `gorm:"column:user_id;comment:点赞人"`
 	CreatedAt time.Time `gorm:"column:created_at;comment:点赞时间"`
 }
 
@@ -146,7 +148,8 @@ func (r *Notice) Entity() *entity.Notice {
 
 // Setting maps table moment_settings.
 type Setting struct {
-	UserID         int64     `gorm:"column:user_id;primaryKey;comment:用户 users.id"`
+	ID             int64     `gorm:"column:id;primaryKey;autoIncrement;comment:行 id，表内自增，仅内部用；业务唯一键是 user_id"`
+	UserID         int64     `gorm:"column:user_id;comment:用户 users.id"`
 	CoverKey       string    `gorm:"column:cover_key;comment:封面 object_key，空表示未设"`
 	VisibleDays    int16     `gorm:"column:visible_days;comment:允许朋友查看范围：0全部 3/30/180 天"`
 	LastReadPostID int64     `gorm:"column:last_read_post_id;comment:发现页红点水位，只增不减"`
@@ -180,8 +183,9 @@ func settingFrom(s *entity.Settings) *Setting {
 
 // Hide maps table moment_hides.
 type Hide struct {
-	UserID  int64 `gorm:"column:user_id;primaryKey;comment:设置方"`
-	PeerID  int64 `gorm:"column:peer_id;primaryKey;comment:对方"`
+	ID      int64 `gorm:"column:id;primaryKey;autoIncrement;comment:行 id，表内自增，仅内部用；业务唯一键是 (user_id, peer_id)"`
+	UserID  int64 `gorm:"column:user_id;comment:设置方"`
+	PeerID  int64 `gorm:"column:peer_id;comment:对方"`
 	HideHim bool  `gorm:"column:hide_him;comment:1=不看他（Feed 去掉对方）"`
 	HideMe  bool  `gorm:"column:hide_me;comment:1=不让他看"`
 }
diff --git a/internal/module/moment/model/write.go b/internal/module/moment/model/write.go
index f9ba8c1..d3b3965 100644
--- a/internal/module/moment/model/write.go
+++ b/internal/module/moment/model/write.go
@@ -79,7 +79,10 @@ func (m *Repo) AddLike(ctx context.Context, like *entity.Like) (bool, error) {
 	}
 	created := false
 	err = db.Transaction(func(tx *gorm.DB) error {
-		res := tx.Clauses(clause.OnConflict{DoNothing: true}).Create(&row)
+		res := tx.Clauses(clause.OnConflict{
+			Columns:   []clause.Column{{Name: "post_id"}, {Name: "user_id"}},
+			DoNothing: true,
+		}).Create(&row)
 		if res.Error != nil {
 			return mapDBErr(res.Error)
 		}
@@ -197,7 +200,12 @@ func (m *Repo) UpsertSettings(ctx context.Context, s *entity.Settings) error {
 	if row.UpdatedAt.IsZero() {
 		row.UpdatedAt = time.Now()
 	}
-	return mapDBErr(db.Save(row).Error)
+	return mapDBErr(db.Clauses(clause.OnConflict{
+		Columns: []clause.Column{{Name: "user_id"}},
+		DoUpdates: clause.AssignmentColumns([]string{
+			"cover_key", "visible_days", "last_read_post_id", "updated_at",
+		}),
+	}).Create(row).Error)
 }
 
 func (m *Repo) AdvanceRead(ctx context.Context, userID, postID int64) error {
diff --git a/internal/module/sync/model/device_sync_cursor.go b/internal/module/sync/model/device_sync_cursor.go
index c07da11..4762288 100644
--- a/internal/module/sync/model/device_sync_cursor.go
+++ b/internal/module/sync/model/device_sync_cursor.go
@@ -4,8 +4,9 @@ import "time"
 
 // DeviceSyncCursor maps table device_sync_cursors.
 type DeviceSyncCursor struct {
-	UserID      int64     `gorm:"column:user_id;primaryKey;comment:用户 id"`
-	DeviceID    int64     `gorm:"column:device_id;primaryKey;comment:设备 id"`
+	ID          int64     `gorm:"column:id;primaryKey;autoIncrement;comment:行 id，表内自增，仅内部用；业务唯一键是 (user_id, device_id)"`
+	UserID      int64     `gorm:"column:user_id;comment:用户 id"`
+	DeviceID    int64     `gorm:"column:device_id;comment:设备 id"`
 	MailboxSeq  int64     `gorm:"column:mailbox_seq;comment:该设备已同步到的 mailbox_events.seq"`
 	DialogScore int64     `gorm:"column:dialog_score;comment:会话列表 Redis ZSET 游标"`
 	UpdatedAt   time.Time `gorm:"column:updated_at;comment:游标更新时间"`
diff --git a/internal/module/sync/model/store.go b/internal/module/sync/model/store.go
index d44bf28..55b33de 100644
--- a/internal/module/sync/model/store.go
+++ b/internal/module/sync/model/store.go
@@ -7,6 +7,7 @@ import (
 
 	mysqldriver "github.com/go-sql-driver/mysql"
 	"gorm.io/gorm"
+	"gorm.io/gorm/clause"
 
 	"spark-server/internal/module/sync/entity"
 	"spark-server/internal/pkg/errs"
@@ -119,5 +120,8 @@ func (s *Store) SaveCursor(ctx context.Context, userID int64, deviceID uint64, m
 		UserID: userID, DeviceID: int64(deviceID),
 		MailboxSeq: mailboxSeq, DialogScore: dialogScore, UpdatedAt: time.Now(),
 	}
-	return mapDBErr(db.Save(&row).Error)
+	return mapDBErr(db.Clauses(clause.OnConflict{
+		Columns:   []clause.Column{{Name: "user_id"}, {Name: "device_id"}},
+		DoUpdates: clause.AssignmentColumns([]string{"mailbox_seq", "dialog_score", "updated_at"}),
+	}).Create(&row).Error)
 }
diff --git a/internal/module/user/model/user_email.go b/internal/module/user/model/user_email.go
index 519217a..8b815b8 100644
--- a/internal/module/user/model/user_email.go
+++ b/internal/module/user/model/user_email.go
@@ -11,7 +11,8 @@ import (
 
 // UserEmail maps table user_emails: one normalized email to one user.
 type UserEmail struct {
-	Email     string    `gorm:"column:email;primaryKey;comment:规范化后的小写邮箱，登录账号"`
+	ID        int64     `gorm:"column:id;primaryKey;autoIncrement;comment:行 id，表内自增，仅内部用；业务唯一键是 email"`
+	Email     string    `gorm:"column:email;comment:规范化后的小写邮箱，登录账号"`
 	UserID    int64     `gorm:"column:user_id;comment:绑定的 users.id，一对一"`
 	CreatedAt time.Time `gorm:"column:created_at;comment:绑定时间"`
 }
diff --git a/migrations/0016_row_autoincrement_id.sql b/migrations/0016_row_autoincrement_id.sql
new file mode 100644
index 0000000..6680a4d
--- /dev/null
+++ b/migrations/0016_row_autoincrement_id.sql
@@ -0,0 +1,63 @@
+-- Junction / mapping tables get a table-local AUTO_INCREMENT row id.
+-- Business uniqueness stays UNIQUE (same columns as the old composite PK).
+-- Snowflake PKs (users / messages / conversations / moments posts) are unchanged.
+
+ALTER TABLE user_emails
+    DROP PRIMARY KEY,
+    ADD COLUMN id BIGINT NOT NULL AUTO_INCREMENT COMMENT '行 id，表内自增，仅内部用；业务唯一键是 email' FIRST,
+    ADD PRIMARY KEY (id),
+    ADD UNIQUE KEY uk_email (email);
+
+ALTER TABLE p2p_conversations
+    DROP PRIMARY KEY,
+    ADD COLUMN id BIGINT NOT NULL AUTO_INCREMENT COMMENT '行 id，表内自增，仅内部用；业务唯一键是 (user_small, user_big)' FIRST,
+    ADD PRIMARY KEY (id),
+    ADD UNIQUE KEY uk_p2p_users (user_small, user_big);
+
+ALTER TABLE conversation_members
+    DROP PRIMARY KEY,
+    ADD COLUMN id BIGINT NOT NULL AUTO_INCREMENT COMMENT '行 id，表内自增，仅内部用；业务唯一键是 (conversation_id, user_id)' FIRST,
+    ADD PRIMARY KEY (id),
+    ADD UNIQUE KEY uk_conversation_members (conversation_id, user_id);
+
+ALTER TABLE device_sync_cursors
+    DROP PRIMARY KEY,
+    ADD COLUMN id BIGINT NOT NULL AUTO_INCREMENT COMMENT '行 id，表内自增，仅内部用；业务唯一键是 (user_id, device_id)' FIRST,
+    ADD PRIMARY KEY (id),
+    ADD UNIQUE KEY uk_user_device (user_id, device_id);
+
+ALTER TABLE group_members
+    DROP PRIMARY KEY,
+    ADD COLUMN id BIGINT NOT NULL AUTO_INCREMENT COMMENT '行 id，表内自增，仅内部用；业务唯一键是 (group_id, user_id)' FIRST,
+    ADD PRIMARY KEY (id),
+    ADD UNIQUE KEY uk_group_members (group_id, user_id);
+
+ALTER TABLE message_deletes
+    DROP PRIMARY KEY,
+    ADD COLUMN id BIGINT NOT NULL AUTO_INCREMENT COMMENT '行 id，表内自增，仅内部用；业务唯一键是 (user_id, msg_id)' FIRST,
+    ADD PRIMARY KEY (id),
+    ADD UNIQUE KEY uk_user_msg (user_id, msg_id);
+
+ALTER TABLE moment_audience
+    DROP PRIMARY KEY,
+    ADD COLUMN id BIGINT NOT NULL AUTO_INCREMENT COMMENT '行 id，表内自增，仅内部用；业务唯一键是 (post_id, peer_id)' FIRST,
+    ADD PRIMARY KEY (id),
+    ADD UNIQUE KEY uk_post_peer (post_id, peer_id);
+
+ALTER TABLE moment_likes
+    DROP PRIMARY KEY,
+    ADD COLUMN id BIGINT NOT NULL AUTO_INCREMENT COMMENT '行 id，表内自增，仅内部用；业务唯一键是 (post_id, user_id)' FIRST,
+    ADD PRIMARY KEY (id),
+    ADD UNIQUE KEY uk_post_user (post_id, user_id);
+
+ALTER TABLE moment_settings
+    DROP PRIMARY KEY,
+    ADD COLUMN id BIGINT NOT NULL AUTO_INCREMENT COMMENT '行 id，表内自增，仅内部用；业务唯一键是 user_id' FIRST,
+    ADD PRIMARY KEY (id),
+    ADD UNIQUE KEY uk_user_id (user_id);
+
+ALTER TABLE moment_hides
+    DROP PRIMARY KEY,
+    ADD COLUMN id BIGINT NOT NULL AUTO_INCREMENT COMMENT '行 id，表内自增，仅内部用；业务唯一键是 (user_id, peer_id)' FIRST,
+    ADD PRIMARY KEY (id),
+    ADD UNIQUE KEY uk_user_peer (user_id, peer_id);