iceberg: create missing metadata parent directories exclusively

saveMetadataBlob created each missing directory on the way to the metadata
directory with a plain CreateEntry after a lookup. A table directory another
create had made and written its record onto since the lookup was replaced by a
bare directory, erasing that record.

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

weed/s3api/iceberg/iceberg_create_table_conflict_test.go

@@ -940,6 +940,26 @@ func TestFinalizeCreateOnCommitLosesToTableWithoutLocation(t *testing.T) {
 	e.assertWinnerRecord("", winnerUUID)
 }
 
+// A table directory another create made and wrote its record onto after this
+// writer's lookup missed it keeps that record when a metadata file is staged.
+func TestSaveMetadataBlobKeepsATableDirectoryCreatedSinceTheLookup(t *testing.T) {
+	e := newConflictEnv(t)
+	namespaceDir := path.Join(s3tables.TablesPath, conflictBucket, conflictNamespace)
+	record := `{"Name":"` + conflictTable + `"}`
+	e.hooks.beforeCreate = func(req *filer_pb.CreateEntryRequest) {
+		if req.Directory == namespaceDir && req.Entry.Name == conflictTable {
+			e.hooks.beforeCreate = nil
+			e.filer.Put(namespaceDir, conflictTable, map[string][]byte{s3tables.ExtendedKeyMetadata: []byte(record)})
+		}
+	}
+	if err := e.server.saveMetadataBlob(t.Context(), conflictBucket, path.Join(conflictNamespace, conflictTable), "v1.metadata.json", []byte("{}"), "application/json", true, nil); err != nil {
+		t.Fatalf("save metadata: %v", err)
+	}
+	if got := e.filer.Get(namespaceDir, conflictTable); got == nil || string(got.Extended[s3tables.ExtendedKeyMetadata]) != record {
+		t.Errorf("table record replaced by the directory create: %+v", got)
+	}
+}
+
 // Two stage-create commits for one name: one creates the table and the other is
 // told it lost, and the file the catalog points at belongs to the winner.
 func TestConcurrentFinalizeCreateOnCommitHasOneWinner(t *testing.T) {

weed/s3api/iceberg/metadata_files.go

@@ -68,9 +68,11 @@ func (s *Server) saveMetadataBlob(ctx context.Context, bucketName, tablePath, me
 				return fmt.Errorf("lookup %s failed: %w", errorContext, err)
 			}
 
-			// If lookup fails with ErrNotFound, try to create the directory.
+			// Exclusive, so a directory created since the lookup keeps the
+			// record a table create may have written onto it.
 			resp, createErr := client.CreateEntry(opCtx, &filer_pb.CreateEntryRequest{
 				Directory: parent,
+				OExcl:     true,
 				Entry: &filer_pb.Entry{
 					Name:        name,
 					IsDirectory: true,