Unfortunately the suggestion was not helpful—it is no mystery what the error is (insufficient permissions to access the DBFS root location). What remains a mystery, and the point of my question, is whether there is a certain configuration of shared clusters that is required in order to make the DBFS root location accessible. I ask this question here in this forum because I have not yet found in the Databricks documentation a discussion of this question, and because the terraform provider I'm using does not list any cluster configuration options which seem relevant to making sure the DBFS root location (or any DBFS filesystem utils) are available on a shared cluster.