Reject negative or fractional index in page.move

Found while testing crates/engine/src/cmd/page.rs:132

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

crates/engine/src/cmd/page.rs

@@ -129,7 +129,7 @@ pub fn specs() -> Vec<CommandSpec> {
         }),
         spec!("page.move", "Move page", "{id?, index}", true, |s, p| {
             let id = id(p, "id").unwrap_or(s.page()?);
-            let k = req_num("page.move", p, "index")?.max(0.0) as usize;
+            let k = req_index("page.move", p, "index")?;
             let doc = s.doc_mut()?;
             if !doc.pages.contains(&id) {
                 return Err(bad("page.move", format!("{id} is not a page")));

crates/engine/src/panels_behaviour_tests.rs

@@ -393,6 +393,20 @@ fn page_select_and_doc_switch_refuse_negative_or_fractional_indexes() {
     }
 }
 
+#[test]
+fn page_move_refuses_negative_or_fractional_indexes() {
+    let mut s = Session::new();
+    ex(&mut s, "page.add", json!({}));
+    let p3 = id(&ex(&mut s, "page.add", json!({})));
+    let before = pages(&mut s);
+    for bad_index in [json!(-1), json!(1.5)] {
+        assert!(s.execute("page.move", &json!({"id": p3, "index": bad_index})).is_err(), "page.move index {bad_index} must fail");
+        assert_eq!(pages(&mut s), before, "page.move index {bad_index} leaves the order alone");
+    }
+    ex(&mut s, "page.move", json!({"id": p3, "index": 0}));
+    assert_eq!(pages(&mut s)[0]["id"], json!(p3), "a valid index still moves the page");
+}
+
 #[test]
 fn assets_panel_lists_files_and_drops_by_the_documented_rules() {
     let mut s = Session::new();