feat(media): 作品保存恢复 - 按原任务重试交付并避免重复生成计费

backend/internal/database/migrations.go

@@ -11,7 +11,7 @@ import (
 	"gorm.io/gorm"
 )
 
-const CurrentSchemaVersion int64 = 33
+const CurrentSchemaVersion int64 = 34
 
 const baselineSchemaChecksum = "sha256:open-ai-canvas-schema-v1-20260830"
 const schemaMigrationAppliedAtIndexChecksum = "sha256:schema-migrations-applied-at-index-v2-20260830"
@@ -107,6 +107,16 @@ var schemaMigrations = []migration{
 	}},
 	{version: 32, name: "channel_model_tags", checksum: "sha256:channel-model-tags-v32", apply: migrateChannelModelTags},
 	{version: 33, name: "oauth_state_accepted_terms", checksum: "sha256:oauth-state-accepted-terms-v33", apply: migrateOAuthStateAcceptedTerms},
+	{version: 34, name: "task_media_recovery", checksum: "sha256:task-media-recovery-v34", apply: func(tx *gorm.DB) error {
+		for _, field := range []string{"MediaRecoveryJSON", "MediaStage"} {
+			if !tx.Migrator().HasColumn(&model.Task{}, field) {
+				if err := tx.Migrator().AddColumn(&model.Task{}, field); err != nil {
+					return err
+				}
+			}
+		}
+		return nil
+	}},
 }
 
 func migrateChannelModelTags(tx *gorm.DB) error {

backend/internal/database/task_media_recovery_test.go

@@ -0,0 +1,38 @@
+package database
+
+import (
+	"infinite-canvas/backend/internal/model"
+	"testing"
+)
+
+func TestTaskMediaRecoveryMigrationPreservesHistoricalTasks(t *testing.T) {
+	db, err := Open(Config{Driver: "sqlite", DSN: ":memory:"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	sqlDB, _ := db.DB()
+	t.Cleanup(func() { _ = sqlDB.Close() })
+	if err := db.Exec(`CREATE TABLE tasks (id TEXT PRIMARY KEY, status TEXT, error TEXT)`).Error; err != nil {
+		t.Fatal(err)
+	}
+	if err := db.Exec(`INSERT INTO tasks VALUES ('old-task', 'failed', 'download failed')`).Error; err != nil {
+		t.Fatal(err)
+	}
+	for i := 0; i < 2; i++ {
+		if err := schemaMigrations[33].apply(db); err != nil {
+			t.Fatal(err)
+		}
+	}
+	var task model.Task
+	if err := db.First(&task, "id = ?", "old-task").Error; err != nil {
+		t.Fatal(err)
+	}
+	if task.Status != model.TaskStatusFailed || task.Error != "download failed" || task.MediaRecoveryJSON != "" || task.MediaStage != "" {
+		t.Fatalf("migration rewrote historical task: %+v", task)
+	}
+	for _, field := range []string{"media_stage", "media_recovery_json"} {
+		if !db.Migrator().HasColumn(&model.Task{}, field) {
+			t.Fatalf("missing %s", field)
+		}
+	}
+}