feat: a late packet backfills the hole it left, values only

src/acquisition.hpp

@@ -61,6 +61,12 @@ class Acquisition {
   void reserve_hole(std::uint32_t missing, const Partition& part,
                     const std::vector<ChannelInfo>& channels, BufferStore& store, u64 g);
 
+  /// Writes a late frame's values into the NaN-filled holes their counter addresses,
+  /// amending the value ring directly (producer path) and queuing pyramid amends for
+  /// `ChannelBuffer::acquire()` to apply on the consumer thread.
+  void backfill_from(const udps_frame_t* frame, const Partition& part,
+                     const std::vector<ChannelInfo>& channels, BufferStore& store, u64 g);
+
   ScopeModel& model_;
   Config cfg_;
   udps_client* client_ = nullptr;