fix(canvas): 画布 - 防止旧内容覆盖并支持版本历史恢复

backend/internal/model/models_canvas_history.go

@@ -0,0 +1,25 @@
+package model
+
+import "time"
+
+// CanvasSnapshot stores document structure only; media stays in Resource storage.
+type CanvasSnapshot struct {
+	ID               string    `json:"id" gorm:"primaryKey;size:36"`
+	CanvasID         string    `json:"canvasId" gorm:"size:80;not null;uniqueIndex:idx_canvas_snapshot_revision,priority:1;index:idx_canvas_snapshot_created,priority:1"`
+	UserID           string    `json:"-" gorm:"size:36;not null;index"`
+	Revision         int64     `json:"revision" gorm:"not null;uniqueIndex:idx_canvas_snapshot_revision,priority:2"`
+	Title            string    `json:"title" gorm:"size:240"`
+	NodeCount        int       `json:"nodeCount"`
+	ConnectionCount  int       `json:"connectionCount"`
+	PayloadBytes     int       `json:"payloadBytes"`
+	PayloadJSON      string    `json:"-" gorm:"type:text;not null"`
+	Reason           string    `json:"reason" gorm:"size:24"`
+	ContentUpdatedAt time.Time `json:"contentUpdatedAt"`
+	CreatedAt        time.Time `json:"createdAt" gorm:"not null;index:idx_canvas_snapshot_created,priority:2"`
+}
+
+type CanvasSnapshotResource struct {
+	SnapshotID string    `json:"-" gorm:"primaryKey;size:36"`
+	ResourceID string    `json:"-" gorm:"primaryKey;size:36;index"`
+	Resource   *Resource `json:"-" gorm:"foreignKey:ResourceID;constraint:OnDelete:RESTRICT"`
+}

backend/internal/model/models_project.go

@@ -374,6 +374,7 @@ type CanvasProject struct {
 	ProjectID   string    `json:"projectId,omitempty" gorm:"index;size:36;index:idx_canvas_projects_user_project_updated,priority:2"`
 	Title       string    `json:"title" gorm:"size:240"`
 	PayloadJSON string    `json:"payloadJson" gorm:"type:text"`
+	Revision    int64     `json:"revision" gorm:"not null;default:1"`
 	CreatedAt   time.Time `json:"createdAt"`
 	UpdatedAt   time.Time `json:"updatedAt" gorm:"index:idx_canvas_projects_user_updated,priority:2;index:idx_canvas_projects_user_project_updated,priority:3"`
 }