Variables: Lock Variables' description names the refused import

variable.lock's params text and the doc comment on Variables::locked said every
dataset command still runs while the variables are locked. dataset.import is
refused when its header would define a variable; both texts now say so, as
docs/mcp.md and dataset.import's params already do.

crates/doc/src/variables.rs

@@ -117,7 +117,8 @@ pub struct Variables {
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub active_dataset: Option<String>,
     /// Lock Variables: while set, variables can't be defined, deleted or renamed. Objects can
-    /// still be bound to them and unbound, and datasets still change and apply.
+    /// still be bound to them and unbound, and datasets still change and apply, except that an
+    /// import whose header would define a variable is refused.
     #[serde(default, skip_serializing_if = "std::ops::Not::not")]
     pub locked: bool,
 }

crates/engine/src/cmd/variablecmds.rs

@@ -641,7 +641,7 @@ pub fn specs() -> Vec<CommandSpec> {
             "Lock Variables",
             ["Window", "Variables"],
             None,
-            "{locked?: bool} lock or unlock the variables (default: toggle); saved with the document; a change is one undo step. While locked, variable.define, variable.delete, variable.rename, variable.make…Dynamic and a variable.loadLibrary that would delete or define a variable are refused; binding, unbinding and the dataset commands still run → {locked}",
+            "{locked?: bool} lock or unlock the variables (default: toggle); saved with the document; a change is one undo step. While locked, variable.define, variable.delete, variable.rename, variable.make…Dynamic and a variable.loadLibrary that would delete or define a variable are refused; binding, unbinding and the dataset commands still run, except a dataset.import whose header would define a variable → {locked}",
             has_doc,
             lock
         ),

crates/engine/src/tests/variables.rs

@@ -409,7 +409,8 @@ fn make_dynamic_errors_name_the_command() {
 }
 
 /// Lock Variables refuses defining, deleting and renaming variables, Make … Dynamic included,
-/// while binding, unbinding and the dataset commands still run.
+/// while binding, unbinding and the dataset commands still run (an import that would define a
+/// variable is refused; see `locked_variables_refuse_header_cells_that_define_variables`).
 #[test]
 fn locked_variables_refuse_new_deleted_and_renamed_variables() {
     let mut s = session();
@@ -1324,6 +1325,14 @@ fn locked_variables_refuse_header_cells_that_define_variables() {
     assert_eq!(imp["defined"], json!(["New"]));
 }
 
+/// `variable.lock`'s params text names the dataset command it refuses: an import whose header
+/// would define a variable.
+#[test]
+fn the_lock_params_text_names_the_refused_import() {
+    let params = cmd::find_command("variable.lock").unwrap().params;
+    assert!(params.contains("the dataset commands still run, except a dataset.import whose header would define a variable"), "{params}");
+}
+
 /// Import / export datasets as CSV: header `name` then variables; round-trip keeps values.
 #[test]
 fn datasets_csv_round_trips_and_rejects_bad_input() {