allow skipping from non-repeated header on lack of space

Can lead to orphans, but without enough space, anything goes.

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

@@ -1376,14 +1376,13 @@ impl<'a> GridLayouter<'a> {
         // endlessly repeated) when subtracting header and footer height.
         //
         // See 'check_for_unbreakable_rows' as for why we're using
-        // 'header_height' to predict header height and not
-        // 'repeating_header_height'.
+        // 'repeating_header_height' to predict header height.
         let height = frame.height();
         while self.unbreakable_rows_left == 0
             && !self.regions.size.y.fits(height)
             && may_progress_with_offset(
                 self.regions,
-                self.current.header_height + self.current.footer_height,
+                self.current.repeating_header_height + self.current.footer_height,
             )
         {
             self.finish_region(engine, false)?;
@@ -1571,11 +1570,9 @@ impl<'a> GridLayouter<'a> {
                 && self.current.lrows.is_empty()
                 && may_progress_with_offset(
                     self.regions,
-                    // This header height isn't doing much as we just
-                    // confirmed that there are no headers in this region,
-                    // but let's keep it here for correctness. It will add
-                    // zero anyway.
-                    self.current.header_height + self.current.footer_height,
+                    // Don't sum header height as we just confirmed that there
+                    // are no headers in this region.
+                    self.current.footer_height,
                 );
 
         let mut laid_out_footer_start = None;

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

@@ -377,7 +377,7 @@ impl<'a> GridLayouter<'a> {
                 // 'header_height == repeating_header_height' here
                 // (there won't be any pending headers at this point, other
                 // than the ones we are about to place).
-                self.current.header_height + self.current.footer_height,
+                self.current.repeating_header_height + self.current.footer_height,
             )
         {
             // Note that, after the first region skip, the new headers will go
@@ -393,7 +393,7 @@ impl<'a> GridLayouter<'a> {
             && self.current.lrows_orphan_snapshot.is_none()
             && may_progress_with_offset(
                 self.regions,
-                self.current.header_height + self.current.footer_height,
+                self.current.repeating_header_height + self.current.footer_height,
             );
 
         if should_snapshot {

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

@@ -258,12 +258,11 @@ impl GridLayouter<'_> {
             while !self.regions.size.y.fits(row_group.height)
                 && may_progress_with_offset(
                     self.regions,
-                    // Note that we consider that the exact same headers and footers will be
-                    // added if we skip like this (blocking other rows from being laid out)
-                    // due to orphan/widow prevention, which explains the usage of
-                    // 'header_height' (include non-repeating but pending headers) rather
-                    // than 'repeating_header_height'.
-                    self.current.header_height + self.current.footer_height,
+                    // Use 'repeating_header_height' (ignoring the height of
+                    // non-repeated headers) to allow skipping if the
+                    // non-repeated header is too large. It will become an
+                    // orphan, but when there is no space left, anything goes.
+                    self.current.repeating_header_height + self.current.footer_height,
                 )
             {
                 self.finish_region(engine, false)?;