Automation: errors name a path outside the read roots by its file name

Under --automation-read-root, an error about a file or folder the client
did not give now names it whole only when it is inside the read roots.
Outside them it names the file or folder by its file name, or as "a file
or folder outside the read roots" when it has none, and keeps the roots
and the reason. A path the client gives stays whole.

This covers a save without a path (the document's own file and the files
written beside it, also inside action.batch, and the refusal to write
over a file read with losses), file.revert, script.listInstalled,
plugin.reload without a path and plugin.list's folder report, and
links.relink with copy (the document's folder, its error when the
document's path has no folder, and the copies in the reply). Export for
Screens' refusal for an export preset's folder uses the same helper.

crates/engine/src/cmd/scripts.rs

@@ -253,7 +253,8 @@ fn list_installed(s: &mut Session, _: &Value) -> Result<Value> {
         return Ok(json!({"folder": null, "scripts": [], "truncated": false, "unreadable": false}));
     };
     let folder = root.to_string_lossy();
-    crate::file_access::check_read(&folder).map_err(EngineError::Other)?;
+    // The Scripts folder is the app's: a refusal names it as the request may see it.
+    crate::file_access::check_read(&folder).map_err(|e| super::fileio::naming_in_error(EngineError::Other(e), &folder))?;
     let listing = script::folder::list(root);
     let scripts: Vec<Value> = listing
         .scripts()