Clarify new single await-push command generation.

Author: GagaLP

include/grid.h

@@ -273,6 +273,8 @@ class region_builder {
 		m_boxes.push_back(box);
 	}
 
+	// Adds a set of boxes to the region builder, skipping empty boxes,
+	// by calling `add` for each element instead of a single `insert(end)`.
 	void add(const box_vector<Dims>& boxes) & {
 		m_boxes.reserve(m_boxes.size() + boxes.size());
 		for(const auto& b : boxes) {

src/command_graph_generator.cc

@@ -402,7 +402,6 @@ void command_graph_generator::generate_await_pushes(batch& current_batch, const
 				if(!box.empty() && !wcs.is_fresh()) { missing_parts_boxes.push_back(box); }
 			}
 
-			// There is data we don't yet have locally. Generate an await push command for it.
 			if(!missing_parts_boxes.empty()) {
 				assert(m_num_nodes > 1);
 				auto& required_boxes = per_buffer_required_boxes[bid]; // allow default-insert
@@ -411,6 +410,7 @@ void command_graph_generator::generate_await_pushes(batch& current_batch, const
 		}
 	}
 
+	// There is data we don't yet have locally. Generate an await push command for it.
 	for(auto& [bid, boxes] : per_buffer_required_boxes) {
 		auto& buffer = m_buffers.at(bid);
 		auto region = std::move(boxes).into_region(); // moved-from after next line!