Integration: Document Setup margins let matching pages follow their parent page (#469)

#469's Document Setup sets every page's and parent page's margins; next's parent-margins model (470aac7d) keeps pages marked local_margins out of later parent edits. After a Document Setup margin edit, pages that now match their parent page (margins and columns) lose the local mark, and parent margins are synced; pages with their own columns stay local.

crates/doc/src/build.rs

@@ -628,6 +628,22 @@ impl Document {
             }
         }
     }
+
+    /// Let document pages whose margins and columns match their parent page's follow it again,
+    /// after an edit that set every page and parent page alike (Document Setup's margins).
+    pub fn unmark_matching_local_margins(&mut self) {
+        for si in 0..self.spreads.len() {
+            for pi in 0..self.spreads[si].pages.len() {
+                let Some(page) = self.spreads[si].pages.get(pi) else { continue };
+                if !page.local_margins || !self.parent_page(page).is_some_and(|q| q.same_margins(page)) {
+                    continue;
+                }
+                if let Some(page) = Arc::make_mut(&mut self.spreads[si]).pages.get_mut(pi) {
+                    page.local_margins = false;
+                }
+            }
+        }
+    }
 }
 
 #[cfg(test)]

crates/engine/src/cmd/layout.rs

@@ -369,6 +369,10 @@ pub fn specs() -> Vec<CommandSpec> {
                                 pg.margins = m;
                             }
                         }
+                        // Pages that now match their parent page follow its later changes; local
+                        // columns stay local.
+                        d.unmark_matching_local_margins();
+                        d.sync_parent_margins();
                     }
                     d.repaginate();
                     if let Some(b) = before {
@@ -1321,6 +1325,22 @@ mod parent_margin_tests {
         (0..d.page_count()).filter_map(|i| d.page(i)).map(|p| (p.margins, p.columns.count, p.local_margins)).collect()
     }
 
+    #[test]
+    fn document_setup_margins_let_pages_follow_their_parent_page_again() {
+        let mut s = Session::new();
+        s.execute("file.new", &json!({"pages": 3})).unwrap();
+        s.execute("layout.marginsAndColumns", &json!({"pages": [1], "margins": 100})).unwrap();
+        s.execute("layout.marginsAndColumns", &json!({"pages": [2], "margins": 100, "columns": 3})).unwrap();
+        s.execute("layout.documentSetup", &json!({"margins": 20})).unwrap();
+        let m = margins(&s.doc().unwrap().doc);
+        let twenty = Margins::uniform(20.0);
+        assert_eq!(m, vec![(twenty, 1, false), (twenty, 1, false), (twenty, 3, true)], "own columns stay local");
+        s.execute("layout.marginsAndColumns", &json!({"parent": "A", "margins": 50})).unwrap();
+        let m = margins(&s.doc().unwrap().doc);
+        assert_eq!(m[1], (Margins::uniform(50.0), 1, false), "page 2 follows the parent page again");
+        assert_eq!(m[2], (twenty, 3, true));
+    }
+
     #[test]
     fn pages_follow_their_parent_pages_margins_unless_set_locally() {
         let mut s = Session::new();