feat(mailbox): 文件夹数据驱动，Web 通过 IMAP 共享服务层操作邮箱

- 新增 mailboxes 表与 MailboxStore（系统文件夹幂等创建，自定义文件夹 CRUD）
- 提取 MailboxService：IMAP 会话与 Web handler 共用，LIST 返回什么 Web 就显示什么
- IMAP 支持 CREATE/DELETE/RENAME/SUBSCRIBE（系统文件夹禁删改、非空禁删）
- Web 删除改为 IMAP 语义：移入 Trash，新增恢复/彻底删除/清空
- 新增通用 /folder/:name 页面与动态侧边栏，/inbox /sent /drafts 保留兼容重定向

internal/store/mailbox_store.go

@@ -0,0 +1,169 @@
+package store
+
+import (
+	"errors"
+
+	"mail_go/internal/db"
+
+	"gorm.io/gorm"
+)
+
+// Mailbox store errors（英文文案：IMAP 响应直接使用，Web 侧另行提示）。
+var (
+	ErrMailboxNotFound = errors.New("No such mailbox")
+	ErrMailboxExists   = errors.New("mailbox already exists")
+	ErrMailboxInvalid  = errors.New("invalid mailbox name")
+	ErrMailboxSystem   = errors.New("system mailbox cannot be deleted or renamed")
+	ErrMailboxNotEmpty = errors.New("mailbox is not empty")
+)
+
+// MailboxStore defines the interface for mailbox (folder) operations.
+type MailboxStore interface {
+	// EnsureSystem 幂等创建用户的系统文件夹（INBOX/Sent/Drafts/Trash）。
+	EnsureSystem(userID uint) error
+	// List 返回用户全部文件夹：系统文件夹按规范顺序在前，
+	// 自定义文件夹按名称升序在后。
+	List(userID uint) ([]db.Mailbox, error)
+	GetByName(userID uint, name string) (*db.Mailbox, error)
+	Create(mb *db.Mailbox) error
+	// Delete 删除空的自定义文件夹（含对应的 mailbox_states 记录）。
+	Delete(userID uint, name string) error
+	// Rename 重命名文件夹并同步迁移其邮件与 mailbox_states 记录。
+	Rename(userID uint, oldName, newName string) error
+	SetSubscribed(userID uint, name string, subscribed bool) error
+}
+
+// mailboxStoreGorm implements MailboxStore using GORM.
+type mailboxStoreGorm struct {
+	db *gorm.DB
+}
+
+// newMailboxStore creates a new GORM-backed MailboxStore.
+func newMailboxStore(database *gorm.DB) MailboxStore {
+	return &mailboxStoreGorm{db: database}
+}
+
+// isSystemMailboxName reports whether name is one of the system mailboxes.
+func isSystemMailboxName(name string) bool {
+	for _, def := range db.SystemMailboxes {
+		if def.Name == name {
+			return true
+		}
+	}
+	return false
+}
+
+// EnsureSystem creates missing system mailboxes for the user.
+// 已存在的行不覆盖：用户此前若已退订某系统文件夹（LSUB），状态保留。
+func (s *mailboxStoreGorm) EnsureSystem(userID uint) error {
+	var existing []db.Mailbox
+	if err := s.db.Where("user_id = ?", userID).Find(&existing).Error; err != nil {
+		return err
+	}
+	have := make(map[string]bool, len(existing))
+	for _, mb := range existing {
+		have[mb.Name] = true
+	}
+	for _, def := range db.SystemMailboxes {
+		if have[def.Name] {
+			continue
+		}
+		mb := &db.Mailbox{
+			UserID:       userID,
+			Name:         def.Name,
+			SpecialUse:   def.SpecialUse,
+			IsSubscribed: true,
+		}
+		if err := s.db.Create(mb).Error; err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// List returns all folders for a user with system folders first.
+func (s *mailboxStoreGorm) List(userID uint) ([]db.Mailbox, error) {
+	var mbs []db.Mailbox
+	if err := s.db.Where("user_id = ?", userID).Order("name").Find(&mbs).Error; err != nil {
+		return nil, err
+	}
+	byName := make(map[string]db.Mailbox, len(mbs))
+	for _, mb := range mbs {
+		byName[mb.Name] = mb
+	}
+	sys := make([]db.Mailbox, 0, len(db.SystemMailboxes))
+	for _, def := range db.SystemMailboxes {
+		if mb, ok := byName[def.Name]; ok {
+			sys = append(sys, mb)
+		}
+	}
+	custom := make([]db.Mailbox, 0, len(mbs))
+	for _, mb := range mbs {
+		if !isSystemMailboxName(mb.Name) {
+			custom = append(custom, mb)
+		}
+	}
+	return append(sys, custom...), nil
+}
+
+// GetByName returns a folder by its exact name.
+func (s *mailboxStoreGorm) GetByName(userID uint, name string) (*db.Mailbox, error) {
+	var mb db.Mailbox
+	if err := s.db.Where("user_id = ? AND name = ?", userID, name).First(&mb).Error; err != nil {
+		return nil, err
+	}
+	return &mb, nil
+}
+
+// Create inserts a new mailbox row.
+func (s *mailboxStoreGorm) Create(mb *db.Mailbox) error {
+	return s.db.Create(mb).Error
+}
+
+// Delete removes an empty mailbox and its mailbox_states record.
+func (s *mailboxStoreGorm) Delete(userID uint, name string) error {
+	return s.db.Transaction(func(tx *gorm.DB) error {
+		var count int64
+		if err := tx.Model(&db.Message{}).
+			Where("user_id = ? AND folder = ?", userID, name).
+			Count(&count).Error; err != nil {
+			return err
+		}
+		if count > 0 {
+			return ErrMailboxNotEmpty
+		}
+		if err := tx.Where("user_id = ? AND name = ?", userID, name).
+			Delete(&db.Mailbox{}).Error; err != nil {
+			return err
+		}
+		return tx.Where("user_id = ? AND folder = ?", userID, name).
+			Delete(&db.MailboxState{}).Error
+	})
+}
+
+// Rename renames a mailbox, moving its messages along with it.
+func (s *mailboxStoreGorm) Rename(userID uint, oldName, newName string) error {
+	return s.db.Transaction(func(tx *gorm.DB) error {
+		if err := tx.Model(&db.Mailbox{}).
+			Where("user_id = ? AND name = ?", userID, oldName).
+			Update("name", newName).Error; err != nil {
+			return err
+		}
+		if err := tx.Model(&db.Message{}).
+			Where("user_id = ? AND folder = ?", userID, oldName).
+			Update("folder", newName).Error; err != nil {
+			return err
+		}
+		// 旧 UIDVALIDITY 不再适用：删除状态记录，下次访问重新生成，
+		// 客户端据此丢弃缓存并全量重同步。
+		return tx.Where("user_id = ? AND folder = ?", userID, oldName).
+			Delete(&db.MailboxState{}).Error
+	})
+}
+
+// SetSubscribed updates the subscription flag of a mailbox.
+func (s *mailboxStoreGorm) SetSubscribed(userID uint, name string, subscribed bool) error {
+	return s.db.Model(&db.Mailbox{}).
+		Where("user_id = ? AND name = ?", userID, name).
+		Update("is_subscribed", subscribed).Error
+}

internal/store/mailbox_store_test.go

@@ -0,0 +1,141 @@
+package store
+
+import (
+	"testing"
+
+	"mail_go/internal/db"
+
+	"gorm.io/driver/sqlite"
+	"gorm.io/gorm"
+)
+
+// newMailboxTestStore 返回基于内存库的 MailboxStore（含 mailboxes 表）。
+func newMailboxTestStore(t *testing.T) (MailboxStore, *gorm.DB) {
+	t.Helper()
+	gdb, err := gorm.Open(sqlite.Open("file::memory:?cache=shared"), &gorm.Config{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := gdb.AutoMigrate(&db.Mailbox{}, &db.Message{}, &db.MailboxState{}); err != nil {
+		t.Fatal(err)
+	}
+	return newMailboxStore(gdb), gdb
+}
+
+// TestMailboxEnsureSystem 验证系统文件夹幂等创建与规范排序。
+func TestMailboxEnsureSystem(t *testing.T) {
+	s, _ := newMailboxTestStore(t)
+
+	if err := s.EnsureSystem(1); err != nil {
+		t.Fatalf("EnsureSystem: %v", err)
+	}
+	// 幂等：再次调用不报错、不产生重复行
+	if err := s.EnsureSystem(1); err != nil {
+		t.Fatalf("EnsureSystem 2nd: %v", err)
+	}
+
+	mbs, err := s.List(1)
+	if err != nil {
+		t.Fatalf("List: %v", err)
+	}
+	if len(mbs) != 4 {
+		t.Fatalf("len(List) = %d, want 4", len(mbs))
+	}
+	want := []string{"INBOX", "Sent", "Drafts", "Trash"}
+	for i, name := range want {
+		if mbs[i].Name != name {
+			t.Fatalf("List[%d] = %q, want %q", i, mbs[i].Name, name)
+		}
+	}
+	if mbs[3].SpecialUse != "Trash" {
+		t.Fatalf("Trash SpecialUse = %q, want Trash", mbs[3].SpecialUse)
+	}
+}
+
+// TestMailboxCustomFolderLifecycle 验证自定义文件夹：创建/排序/非空删除拒绝。
+func TestMailboxCustomFolderLifecycle(t *testing.T) {
+	s, gdb := newMailboxTestStore(t)
+	if err := s.EnsureSystem(1); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := s.Create(&db.Mailbox{UserID: 1, Name: "工作", IsSubscribed: true}); err != nil {
+		t.Fatalf("Create: %v", err)
+	}
+
+	mbs, err := s.List(1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(mbs) != 5 || mbs[4].Name != "工作" {
+		t.Fatalf("custom folder not last: %+v", mbs)
+	}
+
+	// 放一封邮件进去 → 非空文件夹不可删除
+	msg := &db.Message{UserID: 1, Folder: "工作", FromAddr: "a@b", Subject: "s"}
+	if err := gdb.Create(msg).Error; err != nil {
+		t.Fatal(err)
+	}
+	if err := s.Delete(1, "工作"); err != ErrMailboxNotEmpty {
+		t.Fatalf("Delete non-empty mailbox = %v, want ErrMailboxNotEmpty", err)
+	}
+	// 清空后可删除
+	if err := gdb.Where("id = ?", msg.ID).Delete(&db.Message{}).Error; err != nil {
+		t.Fatal(err)
+	}
+	if err := s.Delete(1, "工作"); err != nil {
+		t.Fatalf("Delete empty mailbox: %v", err)
+	}
+	if _, err := s.GetByName(1, "工作"); err == nil {
+		t.Fatal("mailbox should be gone after Delete")
+	}
+}
+
+// TestMailboxRenameMovesMessages 验证重命名同步迁移邮件。
+func TestMailboxRenameMovesMessages(t *testing.T) {
+	s, gdb := newMailboxTestStore(t)
+	if err := s.EnsureSystem(1); err != nil {
+		t.Fatal(err)
+	}
+	if err := s.Create(&db.Mailbox{UserID: 1, Name: "旧名字", IsSubscribed: true}); err != nil {
+		t.Fatal(err)
+	}
+	msg := &db.Message{UserID: 1, Folder: "旧名字", FromAddr: "a@b", Subject: "s"}
+	if err := gdb.Create(msg).Error; err != nil {
+		t.Fatal(err)
+	}
+
+	if err := s.Rename(1, "旧名字", "新名字"); err != nil {
+		t.Fatalf("Rename: %v", err)
+	}
+
+	var count int64
+	if err := gdb.Model(&db.Message{}).
+		Where("user_id = 1 AND folder = ?", "新名字").Count(&count).Error; err != nil {
+		t.Fatal(err)
+	}
+	if count != 1 {
+		t.Fatalf("messages in 新名字 = %d, want 1", count)
+	}
+	if _, err := s.GetByName(1, "旧名字"); err == nil {
+		t.Fatal("old mailbox name should be gone")
+	}
+}
+
+// TestMailboxSubscribed 验证订阅状态写入。
+func TestMailboxSubscribed(t *testing.T) {
+	s, _ := newMailboxTestStore(t)
+	if err := s.EnsureSystem(1); err != nil {
+		t.Fatal(err)
+	}
+	if err := s.SetSubscribed(1, "Trash", false); err != nil {
+		t.Fatalf("SetSubscribed: %v", err)
+	}
+	mb, err := s.GetByName(1, "Trash")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if mb.IsSubscribed {
+		t.Fatal("Trash should be unsubscribed")
+	}
+}

internal/store/stores.go

@@ -16,6 +16,7 @@ type Stores struct {
 	Outbound     OutboundStore
 	ProtocolLogs ProtocolLogStore
 	MailboxState MailboxStateStore
+	Mailboxes    MailboxStore
 }
 
 // NewStores creates a new Stores instance with all GORM-backed implementations.
@@ -29,6 +30,7 @@ func NewStores(database *gorm.DB) *Stores {
 		Outbound:     newOutboundStore(database),
 		ProtocolLogs: newProtocolLogStore(database),
 		MailboxState: newMailboxStateStore(database),
+		Mailboxes:    newMailboxStore(database),
 	}
 }
 
@@ -40,3 +42,4 @@ var _ = db.Attachment{}
 var _ = db.BanEntry{}
 var _ = db.ProtocolLog{}
 var _ = db.MailboxState{}
+var _ = db.Mailbox{}