perfsprint 18→0：strconv.Itoa/FormatInt/FormatUint/FormatBool 替代 fmt.Sprintf、无动词 fmt.Errorf→errors.New、纯字符串拼接。全部语义等价（已核对 diff）。修正 fixer 遗留的 import 问题（引入 goimports 统一整理）。

Result: {"status":"keep","total_issues":56,"golint_canonicalheader":8,"golint_errname":1,"golint_errorlint":12,"golint_forcetypeassert":3,"golint_gosec":0,"golint_intrange":3,"golint_modernize":5,"golint_nilnil":3,"golint_perfsprint":0,"golint_prealloc":3,"golint_recvcheck":7,"golint_usestdlibvars":3,"golint_wastedassign":7,"golint_total":55,"eslint_problems":1,"eslint_errors":0,"eslint_warnings":1,"tsc_errors":0,"measure_s":47}

internal/infra/objectstore/local.go

@@ -5,6 +5,7 @@ package objectstore
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"io"
 	"mime"
@@ -20,7 +21,7 @@ type localBackend struct {
 func newLocalBackend(cfg LocalConfig) (*localBackend, error) {
 	root := filepath.Clean(cfg.Root)
 	if root == "" {
-		return nil, fmt.Errorf("local root is required")
+		return nil, errors.New("local root is required")
 	}
 	return &localBackend{root: root}, nil
 }
@@ -103,7 +104,7 @@ func (b *localBackend) path(key string) (string, error) {
 		}
 		rel, err := filepath.Rel(absRoot, absPath)
 		if err != nil || strings.HasPrefix(rel, "..") {
-			return "", fmt.Errorf("storage key escapes local root")
+			return "", errors.New("storage key escapes local root")
 		}
 		return cleanPath, nil
 	}
@@ -114,7 +115,7 @@ func (b *localBackend) path(key string) (string, error) {
 	path := filepath.Join(b.root, cleanKey)
 	rel, err := filepath.Rel(b.root, path)
 	if err != nil || strings.HasPrefix(rel, "..") {
-		return "", fmt.Errorf("storage key escapes local root")
+		return "", errors.New("storage key escapes local root")
 	}
 	return path, nil
 }