fix: a lost packet reserves the samples it owed instead of vanishing from the timeline

src/acquisition.hpp

@@ -12,6 +12,7 @@
 #include <atomic>
 #include <chrono>
 #include <cstdint>
+#include <limits>
 #include <thread>
 #include <vector>
 
@@ -53,6 +54,13 @@ class Acquisition {
   /// malformed).
   std::uint32_t build_stamps(const udps_frame_t* frame, int time_signal);
 
+  /// Pushes NaN for the `missing` packets' worth of samples that were never delivered,
+  /// advances the decimation accumulators and tick_, records the hole in the model, and
+  /// bumps the hole counters. Called before the frame's own samples so the gap sits
+  /// *ahead* of the data that revealed it.
+  void reserve_hole(std::uint32_t missing, const Partition& part,
+                    const std::vector<ChannelInfo>& channels, BufferStore& store, u64 g);
+
   ScopeModel& model_;
   Config cfg_;
   udps_client* client_ = nullptr;
@@ -101,6 +109,18 @@ class Acquisition {
   std::uint32_t batch_ = 0;
   /// Latches the one warning about a frame whose length disagrees with the stream's first.
   bool warned_batch_ = false;
+  /// The newest counter seen, and the hole's address. Tracked here rather than inferred from
+  /// `frame->lost` because a *late* frame's counter is behind the sequence and must not move
+  /// the mark forward.
+  std::uint32_t last_counter_ = 0;
+  bool have_counter_ = false;
+  /// Last absolute stamp written, epoch-relative, so a reserved hole can continue the
+  /// absolute clock at the declared cadence. The packets that would have carried the real
+  /// stamps never arrived, so a cadence continuation is the only honest value available.
+  double last_abs_stamp_ = 0.0;
+  /// Warn-once latch for a loss past the reservation cap. A member, not a function-local
+  /// `static`, matching the latch Task 2 added for the same reason.
+  bool warned_outage_ = false;
   std::vector<double> stamps_;
   std::vector<double> abs_stamps_;
   /// The decimation filter's state: a running sum per channel (and one for the shared