Do not log an interrupted blob upload as an error (closes #434)

Ctrl-C or SIGTERM cancels the operation's context, which makes the
blob upload in progress fail. The upload step logged that failure at
level ERROR before the interrupted message, so a cancellation the user
asked for read as a storage failure. It now logs the failure only while
the context is still live; only an interrupt cancels it. Any other
upload failure is still logged.

Model: opus-5-5

internal/snapshot/scanner.go

@@ -1861,7 +1861,11 @@ func (s *Scanner) uploadBlobIfNeeded(
 	err = s.storage.PutWithProgress(ctx, blobPath, blobWithReader.Reader,
 		finishedBlob.Compressed, progressCallback)
 	if err != nil {
-		log.Error("Failed to upload blob", "hash", finishedBlob.Hash, "error", err)
+		// Only an interrupt cancels ctx, and the user is told about it,
+		// so an upload it stopped is not logged as a storage failure.
+		if ctx.Err() == nil {
+			log.Error("Failed to upload blob", "hash", finishedBlob.Hash, "error", err)
+		}
 
 		return 0, false, fmt.Errorf("uploading blob to storage: %w", err)
 	}