pending repeating headers at the top are also "repeats"

For "may_progress" purposes.

This avoids an unnecessary additional region break due to them being considered as "non-repeating" before.

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

@@ -76,10 +76,14 @@ pub(super) struct Current {
     /// The initial size of the current region before we started subtracting.
     pub(super) initial: Size,
     /// The height of the region after repeated headers were placed and footers
-    /// prepared.
+    /// prepared. This also includes pending repeating headers from the start,
+    /// even if they were not repeated yet, since they will be repeated in the
+    /// next region anyway (bar orphan prevention).
     ///
     /// This is used to quickly tell if any additional space in the region has
-    /// been occupied since then.
+    /// been occupied since then, meaning that additional space will become
+    /// available after a region break (see
+    /// [`GridLayouter::may_progress_with_repeats`]).
     pub(super) initial_after_repeats: Abs,
     /// Whether `layouter.regions.may_progress()` was `true` at the top of the
     /// region.

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

@@ -329,7 +329,12 @@ impl<'a> GridLayouter<'a> {
         self.current.repeated_header_rows = self.current.lrows.len();
         self.current.initial_after_repeats = self.regions.size.y;
 
+        let mut has_non_repeated_pending_header = false;
         for header in self.pending_headers {
+            if matches!(header, Repeatable::NotRepeated(_)) {
+                self.current.initial_after_repeats = self.regions.size.y;
+                has_non_repeated_pending_header = true;
+            }
             let header_height =
                 self.layout_header_rows(header.unwrap(), engine, disambiguator, false)?;
             if matches!(header, Repeatable::Repeated(_)) {
@@ -338,6 +343,10 @@ impl<'a> GridLayouter<'a> {
             }
         }
 
+        if !has_non_repeated_pending_header {
+            self.current.initial_after_repeats = self.regions.size.y;
+        }
+
         if !may_progress {
             // Flush pending headers immediately, as placing them again later
             // won't help.
@@ -396,6 +405,8 @@ impl<'a> GridLayouter<'a> {
             self.current.lrows_orphan_snapshot = Some(self.current.lrows.len());
         }
 
+        let mut at_top = self.regions.size.y == self.current.initial_after_repeats;
+
         self.unbreakable_rows_left +=
             total_header_row_count(headers.iter().map(Repeatable::unwrap));
 
@@ -412,6 +423,11 @@ impl<'a> GridLayouter<'a> {
             if !short_lived && matches!(header, Repeatable::Repeated(_)) {
                 self.current.repeating_header_height += header_height;
                 self.current.repeating_header_heights.push(header_height);
+                if at_top {
+                    self.current.initial_after_repeats = self.regions.size.y;
+                }
+            } else {
+                at_top = false;
             }
         }