fix orphan prevention

- Include new headers at the start as part of the region's header rows
- Check if header rows are all rows

crates/typst-layout/src/grid/layouter.rs

@@ -1447,7 +1447,7 @@ impl<'a> GridLayouter<'a> {
                     .as_ref()
                     .and_then(Repeatable::as_repeated)
                     .is_none_or(|footer| footer.start != last_header_end)
-                && self.lrows.last().is_some_and(|row| row.index() < last_header_end)
+                && self.lrows.len() == self.current_header_rows
                 && !in_last_with_offset(
                     self.regions,
                     // Since we're trying to find a region where to place all

crates/typst-layout/src/grid/repeated.rs

@@ -373,6 +373,7 @@ impl<'a> GridLayouter<'a> {
         }
 
         if let HeadersToLayout::NewHeaders { headers, short_lived } = headers {
+            let placing_at_the_start = skipped_region || self.lrows.is_empty();
             for header in headers {
                 let header_height =
                     self.layout_header_rows(header.unwrap(), engine, disambiguator)?;
@@ -391,6 +392,11 @@ impl<'a> GridLayouter<'a> {
                     }
                 }
             }
+
+            if placing_at_the_start {
+                // Track header rows at the start of the region.
+                self.current_header_rows = self.lrows.len();
+            }
         }
 
         Ok(())