fix: a re-plan drops the holes it invalidated and restarts the tick they are addressed by

rebuild_locked() replaced the store, so produced() restarted at 0 while the
producer's tick_ kept counting: a hole's slot and tick addressing then described
a buffer that was gone, forget_holes_before() could not retire it, and a
backfill's amend fell outside the ring -- repairing nothing while the hole was
still marked repaired, which is the band reporting the opposite of the truth. A
re-plan generation is the signal rather than the stride/channel-count guard,
which a reconnect with an identical CONFIG leaves unchanged. slot_base_ is left
alone: it is relative mode's clock origin and must not walk backwards when the
user retypes the window.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/acquisition.cpp

@@ -527,6 +527,25 @@ void Acquisition::on_data(const udps_frame_t* frame) {
   BufferStore& store = model_.live();
   const u64 g = part.time_stride;
 
+  // A re-plan replaced the store, so every ring's `produced()` restarted at 0 while `tick_`
+  // kept counting. `backfill_from()` derives a slot index from a hole's `tick_begin`, which is
+  // only an absolute slot index while `tick_ / period == produced()`, so the tick counter has
+  // to restart with the buffer -- otherwise the amend lands outside the ring, repairs nothing,
+  // and the hole is still marked repaired, which is the band saying the opposite of the truth.
+  // The generation is the signal rather than the stride/channel-count comparison below: a
+  // reconnect with an identical CONFIG rebuilds the store leaving both unchanged.
+  // `slot_base_` is deliberately *not* reset -- it is relative mode's clock origin, samples
+  // since the stream began, and relative time must not jump backwards when the user retypes
+  // the window.
+  if (const unsigned gen = model_.plan_generation(); gen != seen_plan_generation_) {
+    seen_plan_generation_ = gen;
+    tick_ = 0;
+    last_tick_ = ~std::uint64_t{0};
+    // Zeroing the stride makes the guard below fire too: the accumulators belong to the group
+    // `tick_` was counting through, so they are stale for the same reason.
+    acc_stride_ = 0;
+  }
+
   // The filter's groups are `g` long, so a re-plan has to start a fresh group rather than
   // finish the one it was in with the wrong length.
   if (acc_stride_ != g || acc_channels_ != channels.size()) {