fix(media): 统一图片结果 URL 化并限制同步 Base64

将上游 URL 直接持久化，内联媒体经对象存储后仅保留 URL 与内部定位元数据；异步轮询、任务详情和幂等重放统一使用零对象读取的 URL 投影，并增加 64KiB 响应门禁。

OpenAI 图片接口接受 url 与 b64_json，同步 Base64 限制为 20MiB 和每 Pod 2 并发；新增历史结果迁移清零门禁、结果指标和 API GOMEMLIMIT。

验证：API go test ./...、go vet、聚焦 race、pnpm openapi、pnpm lint/test/build、迁移安全检查与 docker compose config 均通过。

apps/api/cmd/backfill-binary-results/main.go

@@ -14,6 +14,7 @@ import (
 
 func main() {
 	apply := flag.Bool("apply", false, "persist compacted results; default is dry-run")
+	requireClean := flag.Bool("require-clean", false, "exit non-zero unless a complete dry-run finds no results requiring URL migration")
 	batchSize := flag.Int("batch-size", 100, "rows per batch, maximum 100")
 	maxBatches := flag.Int("max-batches", 10, "maximum batches for one invocation")
 	afterID := flag.String("after-id", "", "resume after this task UUID")
@@ -29,6 +30,10 @@ func main() {
 		logger.Error("invalid backfill bounds", "batchSize", *batchSize, "maxBatches", *maxBatches)
 		os.Exit(1)
 	}
+	if *apply && *requireClean {
+		logger.Error("--apply and --require-clean cannot be combined")
+		os.Exit(1)
+	}
 
 	ctx := context.Background()
 	db, err := store.Connect(ctx, cfg.DatabaseURL)
@@ -42,8 +47,11 @@ func main() {
 	cursor := *afterID
 	scanned := 0
 	matched := 0
+	blockingMatched := 0
 	updated := 0
 	expired := 0
+	expiredLocalPlaceholders := 0
+	complete := false
 	for batch := 0; batch < *maxBatches; batch++ {
 		items, err := db.ListTaskBinaryResultBackfillBatch(ctx, cursor, *batchSize)
 		if err != nil {
@@ -51,26 +59,30 @@ func main() {
 			os.Exit(1)
 		}
 		if len(items) == 0 {
+			complete = true
 			break
 		}
 		for _, item := range items {
 			cursor = item.ID
 			scanned++
-			if !runner.TaskResultHasInlineBinary(item.Result) {
+			if !runner.TaskResultNeedsURLMigration(item.Result) {
 				continue
 			}
 			matched++
+			isExpired := item.FinishedAt.Before(time.Now().Add(-time.Duration(localResultTTLHours(cfg)) * time.Hour))
+			hasLocalPlaceholder := runner.TaskResultHasLocalPlaceholder(item.Result)
+			if isExpired && hasLocalPlaceholder {
+				expiredLocalPlaceholders++
+				if *apply {
+					logger.Warn("skip expired local result placeholder without overwriting stored result", "taskId", item.ID)
+				}
+				continue
+			}
+			blockingMatched++
 			if !*apply {
 				continue
 			}
-			isExpired := item.FinishedAt.Before(time.Now().Add(-time.Duration(localResultTTLHours(cfg)) * time.Hour))
-			var persistent map[string]any
-			var changed bool
-			if isExpired {
-				persistent, changed, err = service.CompactExpiredTaskResultForStorage(ctx, item.ID, item.Result)
-			} else {
-				persistent, changed, err = service.MaterializeTaskResultForStorage(ctx, item.ID, item.Result)
-			}
+			persistent, changed, err := service.MigrateTaskResultToURLs(ctx, item.ID, item.Result)
 			if err != nil {
 				logger.Error("materialize historical binary result failed", "taskId", item.ID, "error", err)
 				os.Exit(1)
@@ -92,6 +104,7 @@ func main() {
 			}
 		}
 		if len(items) < *batchSize {
+			complete = true
 			break
 		}
 	}
@@ -99,10 +112,17 @@ func main() {
 		"apply", *apply,
 		"scanned", scanned,
 		"matched", matched,
+		"blockingMatched", blockingMatched,
 		"updated", updated,
 		"expired", expired,
+		"expiredLocalPlaceholders", expiredLocalPlaceholders,
+		"complete", complete,
 		"resumeAfterId", cursor,
 	)
+	if *requireClean && (!complete || blockingMatched > 0) {
+		logger.Error("binary result URL migration gate failed", "complete", complete, "blockingMatched", blockingMatched, "expiredLocalPlaceholders", expiredLocalPlaceholders, "resumeAfterId", cursor)
+		os.Exit(1)
+	}
 }
 
 func localResultTTLHours(cfg config.Config) int {