Correct downsampling and better layout

src/acquisition.hpp

@@ -77,6 +77,20 @@ class Acquisition {
   double arrival_epoch_ = 0.0;
   bool have_arrival_epoch_ = false;
   std::vector<double> stamps_;
+  /// The decimation filter's state: a running sum per channel (and one for the shared
+  /// clock) over the group of base samples that becomes one stored sample. A boxcar
+  /// average, which is what turns decimation into a *resampling* rather than a stride:
+  /// its first null sits at the stored rate, so what would fold back is attenuated
+  /// instead of reappearing as a false low frequency. Cleared whenever the partition
+  /// changes, since the group length is `time_stride`.
+  std::vector<double> value_acc_;
+  std::vector<std::uint64_t> value_acc_n_;
+  double time_acc_ = 0.0;
+  std::uint64_t time_acc_n_ = 0;
+  /// The partition the accumulators were sized for, so a re-plan resets them rather than
+  /// averaging across the boundary.
+  std::uint64_t acc_stride_ = 0;
+  std::size_t acc_channels_ = 0;
   std::chrono::steady_clock::time_point started_{};
 };