fix: a full reorder ring keeps the arriving packet and counts the overflow, instead of dropping it silently

A packet that needed a slot and found none was neither held nor delivered: no
counter recorded it and the consumer reserved a hole nothing could ever backfill.
It now commits the gap to free a slot and takes the ordering decision once more
against the sequence that commit left behind, bounded to one retry; past that it
is delivered in order with the counters it skipped as its `lost`, never flagged
late, because a packet ahead of the sequence has no hole to be looked up by. A
duplicate can now replace its slot at a full ring, as hold_packet's own comment
already promised, and the 20 ms default window is a named constant.

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

src/acquisition.cpp

@@ -94,6 +94,7 @@ void Acquisition::run() {
     out.resequenced.store(s.late_resequenced, std::memory_order_relaxed);
     out.late.store(s.late_delivered, std::memory_order_relaxed);
     out.stale.store(s.stale_packets, std::memory_order_relaxed);
+    out.overflows.store(s.reorder_overflows, std::memory_order_relaxed);
     out.reconnects.store(s.reconnects, std::memory_order_relaxed);
     out.connected.store(udps_client_is_connected(client_) != 0, std::memory_order_relaxed);
   }

src/model.hpp

@@ -216,6 +216,10 @@ struct StreamStats {
   std::atomic<std::uint64_t> resequenced{0};
   /// Out-of-order packets delivered behind the sequence, past the window.
   std::atomic<std::uint64_t> late{0};
+  /// Times the client's reorder ring was full when a packet needed a slot, so the gap was
+  /// committed early. Nothing is dropped; the window was just shorter than asked for, and a
+  /// non-zero reading is what says the ring is undersized for the stream.
+  std::atomic<std::uint64_t> overflows{0};
   /// Packets the client still refused outright (a duplicate, or any late packet while
   /// resequencing is disabled). Counted since the beginning and displayed nowhere until
   /// now, which is why an inversion had to be inferred from `packets` and `frames`
@@ -547,6 +551,7 @@ class ScopeModel {
   /// Rebuilds buffers from the current channel list. Caller holds `mutex()`.
   void rebuild_locked();
 
+
  private:
   void rebuild_channels();
   /// Re-appends one synthetic signal per math channel, after the stream's own. Called under the

src/ui.cpp

@@ -10559,12 +10559,14 @@ gboolean reseq_probe(gpointer user) {
     }
   }
   std::fprintf(stderr,
-               "[reseq-probe] reseq=%llu late=%llu stale=%llu holes=%llu hole_slots=%llu "
+               "[reseq-probe] reseq=%llu late=%llu stale=%llu overflows=%llu holes=%llu "
+               "hole_slots=%llu "
                "backfilled=%llu open_holes=%zu bands=%zu bands_repaired=%zu nan_slots=%llu "
                "scanned=%llu trigger_in_hole=%d\n",
                static_cast<unsigned long long>(m.stats().resequenced.load()),
                static_cast<unsigned long long>(m.stats().late.load()),
                static_cast<unsigned long long>(m.stats().stale.load()),
+               static_cast<unsigned long long>(m.stats().overflows.load()),
                static_cast<unsigned long long>(m.stats().holes.load()),
                static_cast<unsigned long long>(m.stats().hole_slots.load()),
                static_cast<unsigned long long>(m.stats().backfilled.load()), open_holes, bands,
@@ -10809,8 +10811,8 @@ int run_ui(int argc, char** argv, const Config& cfg, ScopeModel& model, Acquisit
     const Partition& part = model.partition();
     std::printf("[udpscope] frames=%llu packets=%llu gaps=%llu channels=%zu span=%.3fs "
                 "stride=%llu"
-                " reseq=%llu late=%llu stale=%llu holes=%llu hole_slots=%llu backfilled=%llu"
-                "\n",
+                " reseq=%llu late=%llu stale=%llu overflows=%llu holes=%llu hole_slots=%llu"
+                " backfilled=%llu\n",
                 static_cast<unsigned long long>(model.stats().frames.load()),
                 static_cast<unsigned long long>(model.stats().packets.load()),
                 static_cast<unsigned long long>(model.stats().gaps.load()),
@@ -10819,6 +10821,7 @@ int run_ui(int argc, char** argv, const Config& cfg, ScopeModel& model, Acquisit
                 static_cast<unsigned long long>(model.stats().resequenced.load()),
                 static_cast<unsigned long long>(model.stats().late.load()),
                 static_cast<unsigned long long>(model.stats().stale.load()),
+                static_cast<unsigned long long>(model.stats().overflows.load()),
                 static_cast<unsigned long long>(model.stats().holes.load()),
                 static_cast<unsigned long long>(model.stats().hole_slots.load()),
                 static_cast<unsigned long long>(model.stats().backfilled.load()));