chore: baseline snapshot before moderation-strictness feature

Repo .git was damaged (refs/ missing, index truncated, object store near-empty).
Repaired via git init (rebuilt refs), stale index preserved as .git/index.corrupt-20260910.bak,
then full worktree committed as a rollback baseline.

internal/db/message.go

@@ -0,0 +1,132 @@
+package db
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/pkg/errors"
+	"gorm.io/gorm"
+
+	"github.com/tamakyi/TamaBox/internal/dbutil"
+)
+
+var Messages MessageStore
+
+type MessageStore interface {
+	Create(ctx context.Context, opts CreateMessageOptions) (*Message, error)
+	GetByConversationID(ctx context.Context, conversationID uint, cursor *dbutil.Cursor) ([]*Message, error)
+	// GetFirstMessagesByConversationIDs 批量获取多个会话的第一条消息（解决 N+1 查询）
+	GetFirstMessagesByConversationIDs(ctx context.Context, conversationIDs []uint) (map[uint]string, error)
+	// GetAllByConversationIDs 批量获取多个会话的全部消息（导出用，不分页），按 conversation_id 分组。
+	// 将每个会话原本的 1 次查询合并为 1 次 IN 查询，避免 N+1。
+	GetAllByConversationIDs(ctx context.Context, conversationIDs []uint) (map[uint][]*Message, error)
+}
+
+func NewMessageStore(db *gorm.DB) MessageStore {
+	return &messages{db}
+}
+
+type messages struct {
+	*gorm.DB
+}
+
+type Message struct {
+	dbutil.Model
+	ConversationID uint   `gorm:"index:idx_message_conversation" json:"conversation_id"`
+	SenderID       uint   `json:"sender_id"`
+	Content        string `gorm:"type:text" json:"content"`
+	Read           bool   `gorm:"default:false" json:"read"`
+}
+
+type CreateMessageOptions struct {
+	ConversationID uint
+	SenderID       uint
+	Content        string
+}
+
+func (db *messages) Create(ctx context.Context, opts CreateMessageOptions) (*Message, error) {
+	msg := &Message{
+		ConversationID: opts.ConversationID,
+		SenderID:       opts.SenderID,
+		Content:        opts.Content,
+	}
+	if err := db.WithContext(ctx).Create(msg).Error; err != nil {
+		return nil, errors.Wrap(err, "create message")
+	}
+	return msg, nil
+}
+
+func (db *messages) GetByConversationID(ctx context.Context, conversationID uint, cursor *dbutil.Cursor) ([]*Message, error) {
+	var messages []*Message
+	q := db.WithContext(ctx).Where("conversation_id = ?", conversationID)
+
+	limit := 50
+	if cursor != nil {
+		if cursor.Value != nil && fmt.Sprintf("%v", cursor.Value) != "" {
+			q = q.Where("id < ?", cursor.Value)
+		}
+		limit = cursor.Limit()
+	}
+
+	q = q.Order("created_at ASC")
+	q = q.Limit(limit)
+
+	if err := q.Find(&messages).Error; err != nil {
+		return nil, errors.Wrap(err, "get messages")
+	}
+	return messages, nil
+}
+
+// GetFirstMessagesByConversationIDs 批量获取多个会话的第一条消息内容。
+// 使用窗口函数 ROW_NUMBER() 选出每个会话最早的消息，避免 N+1 查询。
+func (db *messages) GetFirstMessagesByConversationIDs(ctx context.Context, conversationIDs []uint) (map[uint]string, error) {
+	if len(conversationIDs) == 0 {
+		return make(map[uint]string), nil
+	}
+
+	// 使用子查询 + ROW_NUMBER 窗口函数获取每个 conversation 的第一条消息
+	// 兼容 MySQL 8+ / PostgreSQL / SQLite 3.25+
+	var results []struct {
+		ConversationID uint   `gorm:"column:conversation_id"`
+		Content        string `gorm:"column:content"`
+	}
+
+	err := db.WithContext(ctx).Raw(`
+		SELECT conversation_id, content FROM (
+			SELECT conversation_id, content,
+				ROW_NUMBER() OVER (PARTITION BY conversation_id ORDER BY created_at ASC) AS rn
+			FROM messages
+			WHERE conversation_id IN ?
+		) sub WHERE rn = 1
+	`, conversationIDs).Scan(&results).Error
+
+	if err != nil {
+		return nil, errors.Wrap(err, "get first messages batch")
+	}
+
+	resultMap := make(map[uint]string, len(results))
+	for _, r := range results {
+		resultMap[r.ConversationID] = r.Content
+	}
+	return resultMap, nil
+}
+
+// GetAllByConversationIDs 批量获取多个会话的全部消息（导出用，不分页），按 conversation_id 分组。
+// 用于账号导出：将每个会话原本的 1 次查询合并为 1 次 IN 查询，避免 N+1。
+func (db *messages) GetAllByConversationIDs(ctx context.Context, conversationIDs []uint) (map[uint][]*Message, error) {
+	result := make(map[uint][]*Message)
+	if len(conversationIDs) == 0 {
+		return result, nil
+	}
+	var items []*Message
+	if err := db.WithContext(ctx).
+		Where("conversation_id IN ?", conversationIDs).
+		Order("conversation_id ASC, created_at ASC").
+		Find(&items).Error; err != nil {
+		return nil, errors.Wrap(err, "get messages by conversation ids")
+	}
+	for _, m := range items {
+		result[m.ConversationID] = append(result[m.ConversationID], m)
+	}
+	return result, nil
+}