LRC-LIB-KEYWORDS: a new keyword set doesn't take another set's name

Saving Recent Keywords as a set under the name of an existing one
(Edit Set… on Recent Keywords) replaced that set's keywords without a
word, while renaming onto a taken name was refused. `keyword.saveSet`
takes `new: true` for a set that must be new, and refuses a name
another set has.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/cmd/keywords.rs

@@ -145,7 +145,7 @@ pub fn specs() -> Vec<CommandSpec> {
             "Save Keyword Set",
             [],
             None,
-            "{name, keywords?: [up to 9, \"\" = an empty slot] (default: the renamed set's, else the current nine), replace?: the set it renames} — replaces a set of that name (or `replace`, in its place) and makes it current",
+            "{name, keywords?: [up to 9, \"\" = an empty slot] (default: the renamed set's, else the current nine), replace?: the set it renames, new?: refuse a name another set has} — replaces a set of that name (or `replace`, in its place) and makes it current",
             always,
             |s, p| {
                 let name = str_param(p, "name")
@@ -184,6 +184,10 @@ pub fn specs() -> Vec<CommandSpec> {
                             *x = set;
                         }
                     }
+                    // a new set (`new`) never takes another set's name
+                    None if bool_or(p, "new", false) && s.keyword_sets.iter().any(|x| same_name(x, &name)) => {
+                        return Err(bad("keyword.saveSet", format!("there is a keyword set “{name}” already")));
+                    }
                     None => match s.keyword_sets.iter_mut().find(|x| same_name(x, &name)) {
                         Some(x) => *x = set,
                         None => s.keyword_sets.push(set),

crates/engine/src/tests_keyword_list.rs

@@ -239,3 +239,14 @@ fn renaming_a_set_alone_keeps_its_keywords() {
     s.execute("keyword.saveSet", &json!({"name": "Ceremonies", "replace": "Weddings"})).unwrap();
     assert_eq!(set_named(&mut s, "Ceremonies")["keywords"], json!(["ceremony"]));
 }
+
+/// A new set (`new: true`, what Edit Set… on Recent Keywords saves) never takes another set's
+/// name: saving over it silently is refused.
+#[test]
+fn a_new_set_doesnt_take_a_sets_name() {
+    let mut s = Session::with_demo();
+    s.execute("keyword.saveSet", &json!({"name": "Travel", "keywords": ["harbour", "lisbon"]})).unwrap();
+    let err = s.execute("keyword.saveSet", &json!({"name": "travel", "new": true, "keywords": ["x"]})).unwrap_err().to_string();
+    assert!(err.contains("already"), "{err}");
+    assert_eq!(set_named(&mut s, "Travel")["keywords"], json!(["harbour", "lisbon"]), "left as it was");
+}