Actions: keep empty path values in ui.inspect's copy of recorded steps

Under a read root, an empty or blank value under a path param, or in a
path param's list, names no path. ui.inspect now keeps it, so a recorded
prefs.set step that clears a folder preference shows the reset.

crates/ui-egui/src/control.rs

@@ -1088,13 +1088,14 @@ fn leave_out_unreadable_pref_steps(command: &str, params: &mut serde_json::Map<S
 /// paths the request may not read: the value of a path param
 /// ([`vectorcraft_engine::file_access::is_path_key`]: `path`, `file`, `diffPath`, `destinationFolder`
 /// and the like), each path of a list under such a param, and under any other param, as a key too, a
-/// string written as a path ([`unreadable_path_like`]).
+/// string written as a path ([`unreadable_path_like`]). An empty or blank value names no path and stays.
 fn leave_out_unreadable_params(params: &mut serde_json::Map<String, Value>) {
     use vectorcraft_engine::file_access::is_path_key;
+    let shown = |p: &str| p.trim().is_empty() || readable_value(p);
     params.retain(|key, v| {
         !unreadable_path_like(key)
             && match v.as_str() {
-                Some(p) => !unreadable_path_like(p) && !(is_path_key(key) && !readable_value(p)),
+                Some(p) => !unreadable_path_like(p) && !(is_path_key(key) && !shown(p)),
                 None => true,
             }
     });
@@ -1102,7 +1103,7 @@ fn leave_out_unreadable_params(params: &mut serde_json::Map<String, Value>) {
         if let Value::Array(paths) = v
             && is_path_key(key)
         {
-            paths.retain(|p| p.as_str().is_none_or(readable_value));
+            paths.retain(|p| p.as_str().is_none_or(shown));
         }
         leave_out_unreadable_values(v);
     }

crates/ui-egui/src/control/tests.rs

@@ -311,6 +311,24 @@ fn a_spaced_absolute_path_outside_the_read_root_is_left_out() {
     assert_eq!(params, json!({"keep": inside, "list": []}));
 }
 
+/// Under a read root, an empty or blank value names no path, so a recorded step keeps it under a path
+/// param and in a path param's list, a folder preference reset in a `prefs.set` step's `values`
+/// included; a path outside the root is still left out.
+#[test]
+fn an_empty_path_param_stays_under_a_read_root() {
+    let base = crate::tests_folder::Folder::new("unreadable-empty");
+    std::fs::create_dir_all(base.join("in")).unwrap();
+    let roots = vectorcraft_engine::file_access::AutomationRoots::new(&[&base.join("in")], &[]).unwrap();
+    let mut params = json!({
+        "values": {"fontsFolder": "", "templatesFolder": " ", "recoveryFolder": "/outside/root/x"},
+        "path": "", "destinationFolder": " ", "files": ["", "/outside/root/y"],
+    });
+    vectorcraft_engine::file_access::confine(roots.as_ref(), || {
+        super::leave_out_unreadable_step("prefs.set", params.as_object_mut().unwrap());
+    });
+    assert_eq!(params, json!({"values": {"fontsFolder": "", "templatesFolder": " "}, "path": "", "destinationFolder": " ", "files": [""]}));
+}
+
 /// Without a read root, a `file:` URL that names another host may be read, and a recorded step keeps
 /// it.
 #[test]