fix(ilm): count a version under old and healed headers as one revision

The version history that an ILM expiry reads accepts a version only
when one revision of it is on more than half of the drives and on its
read quorum, and a revision was the header as the drive stores it plus
a digest of the metadata. A drive holds the header that the release
which wrote the version there stored: before RELEASE.2024-04-28
without erasure coding, and until RELEASE.2022-01-25 with a signature
that counted empty part ETags. A heal writes the header of its own
release and leaves the other drives alone. Reads and heal take both
for one version; the history counted two revisions. With 5 to 11 of 16
drives healed (EC:4) neither had the quorum, objectVersions failed
with a read quorum error, and every expiry that reads the history was
refused on each scanner cycle, with nothing to bring the drives
together: every expiry in a versioned bucket with several pools, and
an expiry of all versions of a key with one pool too.

versionRevision now gives the key of an object version the signature
and the erasure coding as the current release computes them from the
decoded metadata. The key of a version this release wrote carries its
header as stored, so its history decides as before, including the
order of versions of one time, which the signature breaks. The digest
covers what both fields say. The stored flags stay in the key: whether
a transitioned version uses its data directory follows the moment a
drive wrote the entry (fileInfoRevisions).

TestPoolsLifecycleHeaderEras accepts both old headers on every count
of healed drives. TestPoolsLifecycleHealedOldHeaders expires a
noncurrent version with two pools, and all versions with one, after
half of the drives were wiped and healed. Both fail before this
change. Drives that differ only in the data directory flag of a
restored version are still two revisions; that is a separate defect.

Co-Authored-By: Claude Fable 5.2 <noreply@anthropic.com>
Signed-off-by: Feng Ruohang <rh@vonng.com>

cmd/erasure-server-pool-lifecycle.go

@@ -187,9 +187,17 @@ type revisionKey struct {
 // input is canonical: each map, including the part checksums of a legacy
 // version, is its own section with its entry count and sorted,
 // length-prefixed entries, since msgp encodes maps in iteration order and an
-// entry must not move between maps unnoticed. The header of a
-// legacy version carries a signature over its per-shard checksums, so the
-// key replaces it with one from the digest.
+// entry must not move between maps unnoticed.
+//
+// A drive holds the header that the release which wrote the version there
+// stored, and a heal writes the one of its own release: headers from before
+// RELEASE.2024-04-28 carry no erasure coding, and the signature counted
+// empty part ETags until RELEASE.2022-01-25. Reads and heal take such drives
+// for one version (matchesNotStrict), and nothing rewrites them. The key has
+// both as the current release computes them from the metadata, so that the
+// header of a version it wrote stays as stored: the signature also orders
+// versions of one time in the merge. The signature of a legacy version is
+// over its per-shard checksums; the key has one from the digest.
 func versionRevision(ver xlMetaV2ShallowVersion, metaV uint8) revisionKey {
 	h := sha256.New()
 	writeUint := func(n int) {
@@ -267,8 +275,12 @@ func versionRevision(ver xlMetaV2ShallowVersion, metaV uint8) revisionKey {
 			section("fields", 1)
 			writeField(bts)
 			h.Sum(key.digest[:0])
-			if v.Type == LegacyType {
+			switch v.Type {
+			case LegacyType:
 				copy(key.header.Signature[:], key.digest[:])
+			case ObjectType:
+				key.header.Signature = v.ObjectV2.Signature()
+				key.header.EcN, key.header.EcM = uint8(v.ObjectV2.ErasureN), uint8(v.ObjectV2.ErasureM)
 			}
 			return key
 		}
@@ -350,7 +362,7 @@ func authoritativeHistory(ctx context.Context, metas [][]xlMetaV2ShallowVersion,
 	// its count, and one that shares the header could stand in for the
 	// accepted one, so the merge only sees the accepted revision of each
 	// version and free versions as they are. It sees the headers of the
-	// keys, which do not differ between the drives of a legacy version.
+	// keys, which do not differ between the drives of a revision.
 	filtered := make([][]xlMetaV2ShallowVersion, len(metas))
 	for i, versions := range metas {
 		for j, ver := range versions {