mount: check the creation time when the base has no inode

An entry without an inode or hard link id matched any replacement at the
same path, so a stale handle could merge into a different file. Without
an inode the merge now needs the same creation time. The filer keeps it
across updates; only a synthesized base has neither and still merges.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

weed/mount/content_flush_condition_test.go

@@ -354,6 +354,18 @@ func TestMergeContentEntry(t *testing.T) {
 		t.Fatal("refused a truncate that shortened an unstamped base chunk")
 	}
 
+	noInode := proto.Clone(base).(*filer_pb.Entry)
+	noInode.Attributes.Inode, noInode.Attributes.Crtime = 0, 5
+	sameFile := proto.Clone(noInode).(*filer_pb.Entry)
+	sameFile.Chunks = append(sameFile.Chunks, stored.Chunks[2])
+	if _, ok := mergeContentEntry(sameFile, noInode, local, local, -1); !ok {
+		t.Fatal("refused an inode-less file with the same creation time")
+	}
+	sameFile.Attributes.Crtime = 6
+	if _, ok := mergeContentEntry(sameFile, noInode, local, local, -1); ok {
+		t.Fatal("merged into an inode-less replacement")
+	}
+
 	empty := flushConditionEntry()
 	inline := proto.Clone(empty).(*filer_pb.Entry)
 	inline.Content = []byte("peer")

weed/mount/weedfs_file_sync.go

@@ -485,13 +485,18 @@ func mergeContentEntry(stored, base, local, sent *filer_pb.Entry, truncatedTo in
 	return merged, true
 }
 
-// sameContentFile reports whether stored is still the regular file base was.
+// sameContentFile reports whether stored is still the regular file base was:
+// the same inode, or for an entry without one, the same creation time. A
+// synthesized base with neither cannot tell.
 func sameContentFile(stored, base *filer_pb.Entry) bool {
 	if stored == nil || base == nil || stored.IsDirectory || !bytes.Equal(stored.HardLinkId, base.HardLinkId) {
 		return false
 	}
-	inode := base.GetAttributes().GetInode()
-	return inode == 0 || stored.GetAttributes().GetInode() == inode
+	if inode := base.GetAttributes().GetInode(); inode != 0 {
+		return stored.GetAttributes().GetInode() == inode
+	}
+	crtime := base.GetAttributes().GetCrtime()
+	return crtime == 0 || stored.GetAttributes().GetCrtime() == crtime
 }
 
 // contentChunkKey identifies a chunk reference: truncation shrinks a chunk in