Update log message to not print

main.go

@@ -691,6 +691,10 @@ func runNewtMain(ctx context.Context) {
 			Platform:       newtPlatform,
 			TLSConfig:      tlsCfg,
 		}); err != nil {
+			if errors.Is(err, updates.ErrAutoUpdateUnsupportedInOfficialContainer) {
+				logger.Debug("checkAndSelfUpdate: auto-update skipped: %v", err)
+				return
+			}
 			logger.Error("Auto-update check failed: %v", err)
 		}
 	}

updates/selfupdate.go

@@ -7,6 +7,7 @@ import (
 	"crypto/tls"
 	"encoding/hex"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"net/http"
@@ -50,6 +51,10 @@ type versionResponse struct {
 	Message string `json:"message"`
 }
 
+// ErrAutoUpdateUnsupportedInOfficialContainer indicates auto-update is not
+// available when running inside official Fossorial container images.
+var ErrAutoUpdateUnsupportedInOfficialContainer = errors.New("auto-update unsupported in official Fossorial container images")
+
 // isOfficialContainer returns true when the process is running inside an
 // official Fossorial-built container image.  The image sets
 // NEWT_SYSTEM_SUBSTRATE="CONTAINER" at build time; users running newt in their own
@@ -113,7 +118,7 @@ func CheckAndSelfUpdate(cfg SelfUpdateConfig) error {
 
 	if isOfficialContainer() {
 		logger.Debug("checkAndSelfUpdate: running inside official container, skipping auto-update")
-		return fmt.Errorf("auto-update is not supported in official Fossorial container images; pull a new image tag instead")
+		return fmt.Errorf("%w; pull a new image tag instead", ErrAutoUpdateUnsupportedInOfficialContainer)
 	}
 
 	if cfg.CurrentVersion == "version_replaceme" {