Unified endpoint for listing files and folders in a directory.

session_id scopes the listing to an isolated run's own prefix (the --cloud copy-back); absent, it lists the shared workspace.

The reply always carries run_scoped, saying which of those two happened. It exists for the copy-back: a deployment predating this parameter ignores the unknown query arg and answers with the SHARED listing, which is indistinguishable from a correctly-scoped empty run unless the answer says so. An isolated run treats a reply without the field as "this server cannot scope me" and drops the store leg rather than exporting another run's files. Never remove it, and never report True on a path that did not resolve through the run-scoped service.