Skip divider rows in Next page and Previous page

Fixes #413

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

crates/engine/src/cmd/view.rs

@@ -138,8 +138,16 @@ fn page_step(s: &mut Session, dir: i64) -> Result<Value> {
     let pages = &ds.doc.pages;
     let i = pages.iter().position(|p| *p == ds.page).unwrap_or(0) as i64;
     let n = pages.len() as i64;
-    let next = (i + dir).clamp(0, n - 1) as usize;
-    let Some(pg) = pages.get(next).copied() else { return ok() };
+    // Dividers never open: step over them, and stay put when only dividers lie ahead.
+    let mut next = i + dir;
+    let pg = loop {
+        let page = usize::try_from(next).ok().and_then(|k| pages.get(k).copied());
+        match page {
+            Some(p) if !ds.doc.is_divider(p) => break p,
+            Some(_) if dir != 0 && next >= 0 && next < n => next += dir,
+            _ => break ds.page,
+        }
+    };
     let ds = s.ds_mut()?;
     ds.page = pg;
     ds.selection.clear();

crates/engine/src/panels_behaviour_tests.rs

@@ -414,3 +414,25 @@ fn duplicating_a_layer_named_past_the_counter_does_not_overflow() {
     assert_eq!(name(&s, dup), "Layer 18446744073709551615 2");
     assert!(s.doc().unwrap().validate().is_empty(), "the document still checks out");
 }
+
+#[test]
+fn page_navigation_skips_dividers() {
+    // A trailing divider: Next page stays on the ordinary page.
+    let mut s = Session::new();
+    let first = s.page().unwrap();
+    let div = id(&ex(&mut s, "page.add", json!({"name": "-"})));
+    assert!(s.execute("page.select", &json!({"id": div})).is_err(), "a divider isn't a page to open");
+    let r = ex(&mut s, "view.nextPage", json!({}));
+    assert_eq!(s.page().unwrap(), first, "Next page doesn't open a trailing divider");
+    assert_eq!(id_of(&r["page"]), Some(first), "the result names the current page");
+    // A middle divider: Previous page crosses it, Next page crosses it back.
+    let later = id(&ex(&mut s, "page.add", json!({"name": "Later"})));
+    assert_eq!(s.page().unwrap(), later);
+    let r = ex(&mut s, "view.prevPage", json!({}));
+    assert_eq!(s.page().unwrap(), first, "Previous page crosses a divider");
+    assert_eq!(id_of(&r["page"]), Some(first));
+    ex(&mut s, "view.nextPage", json!({}));
+    assert_eq!(s.page().unwrap(), later, "Next page crosses a divider");
+    ex(&mut s, "view.nextPage", json!({}));
+    assert_eq!(s.page().unwrap(), later, "Next page stops on the last page");
+}