refactor(*): 平台架构 - 拆分后端领域模块并同步插件协议与模型能力

backend/internal/platform/host.go

@@ -0,0 +1,70 @@
+package platform
+
+import (
+	"time"
+
+	"infinite-canvas/backend/internal/kernel"
+	"infinite-canvas/backend/internal/model"
+	"infinite-canvas/backend/internal/repository"
+)
+
+const TaskWorkerConcurrency = 3
+
+// Host 由组合根注入，避免 platform → app 回环。
+type Host interface {
+	RequireAdmin(user *model.User) error
+	AppendAudit(actor *model.User, action, targetType, targetID, summary string, metadata any) error
+	DesktopLocalChannelsEnabled() bool
+	ChannelConcurrencyLimit(channelID string) (int, error)
+}
+
+type nopHost struct{}
+
+func (nopHost) RequireAdmin(*model.User) error { return nil }
+func (nopHost) AppendAudit(*model.User, string, string, string, string, any) error {
+	return nil
+}
+func (nopHost) DesktopLocalChannelsEnabled() bool { return false }
+func (nopHost) ChannelConcurrencyLimit(string) (int, error) {
+	return 0, nil
+}
+
+type Service struct {
+	repo             *repository.Repository
+	host             Host
+	Coordinator      *Coordinator
+	concurrencyCache *BoundedReadCache[string, RuntimeTaskPolicy]
+}
+
+func New(repo *repository.Repository, coordinator *Coordinator, host Host) *Service {
+	if host == nil {
+		host = nopHost{}
+	}
+	return &Service{
+		repo:             repo,
+		host:             host,
+		Coordinator:      coordinator,
+		concurrencyCache: NewBoundedReadCache[string, RuntimeTaskPolicy](1, 1024, 1, 2*time.Second),
+	}
+}
+
+func (s *Service) requireAdmin(user *model.User) error {
+	if s == nil || s.host == nil {
+		return kernel.Unauthorized("请先登录")
+	}
+	return s.host.RequireAdmin(user)
+}
+
+func (s *Service) appendAdminAudit(actor *model.User, action, targetType, targetID, summary string, metadata any) error {
+	if s == nil || s.host == nil {
+		return nil
+	}
+	return s.host.AppendAudit(actor, action, targetType, targetID, summary, metadata)
+}
+
+func (s *Service) desktopLocalChannelsEnabled() bool {
+	if s == nil || s.host == nil {
+		return false
+	}
+	return s.host.DesktopLocalChannelsEnabled()
+}