Backblaze B2 requires authentication for the list-bucket API; anonymous
access only works for individual public-read objects. The unauthenticated
curl returned AccessDenied, so r-version-s3.txt was always empty and every
R version was rebuilt despite already existing in s3.
Sign the listing request with --aws-sigv4 using the same B2 credentials as
the upload step. Also fix the broken version extraction: the old
substr($NF, 3, 5) ran against the prefixed key and yielded garbage, so the
Build step's grep could never match. Print the actual version on a match
and use a literal index() instead of a regex comparison.
pat-s
eef805bd76