feat: a repaired hole keeps a fainter band, so a report is not a false accusation

src/acquisition.cpp

@@ -875,8 +875,8 @@ void Acquisition::backfill_from(const udps_frame_t* frame, const Partition& part
   // and resequencing are one design. A stamp could not answer it -- the packet's own stamps
   // are a claim about a timeline the ring has moved past -- but the counter indexes the
   // reservation table directly.
-  const Hole* hole = nullptr;
-  for (const Hole& h : model_.holes()) {
+  Hole* hole = nullptr;
+  for (Hole& h : model_.holes()) {
     if (frame->counter >= h.counter_first && frame->counter < h.counter_first + h.packets) {
       hole = &h;
       break;
@@ -928,6 +928,12 @@ void Acquisition::backfill_from(const udps_frame_t* frame, const Partition& part
       }
     }
   }
+  // This packet's share of the hole has been delivered, whatever the ring still retains of it.
+  // Marked on *arrival* and not on `filled`: a decimation coarse enough that no whole slot lies
+  // inside one packet repairs no slot at all, and keying off `filled` would leave such a hole
+  // permanently unrepairable -- a solid band over data that is all there, which is the exact
+  // defect this task closes.
+  ++hole->filled_packets;
   model_.stats().backfilled.fetch_add(filled, std::memory_order_relaxed);
 }