The _shardsvrRenameIndexMetadata command was introduced for use with the global indexes code.

Since the global indexes feature flag was never enabled, the command was effectively a no-op. However, this command is invoked by 8.0 binaries during renameCollection DDL.

This means that 8.0 binaries send and expect a response for _shardsvrRenameIndexMetadata, even though the command does nothing due to the feature flag being disabled.

We need to retain this command until version 9.0 becomes the last LTS release, at which point we can safely remove it, knowing that no nodes will attempt to call it.