Fix MC labels carried over between sectors in the TPC digitizer

This fixes a problem in the TPC DigitContainer reset and adds a unit test.

- With DigiParams.maxOrbitsToDigitize set, time bins beyond the timeframe end stay in the container after the final flush.
- reset() cleared only their charges, so their MC labels were attached to digits of the next sector processed by the same lane.
- reset() now deletes all remaining time bins, and the destructor frees them.
- testTPCDigitContainerReset checks that no label of one sector reaches the next.

https://its.cern.ch/jira/browse/O2-7310

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: sawenzel

Detectors/TPC/simulation/include/TPCSimulation/DigitContainer.h

@@ -45,7 +45,12 @@ class DigitContainer
   DigitContainer();
 
   /// Destructor
-  ~DigitContainer() = default;
+  ~DigitContainer()
+  {
+    for (auto time : mTimeBins) {
+      delete time;
+    }
+  }
 
   /// Reset the container
   void reset();
@@ -115,11 +120,11 @@ inline void DigitContainer::reset()
 {
   mFirstTimeBin = 0;
   mEffectiveTimeBin = 0;
-  for (auto& time : mTimeBins) {
-    if (time) {
-      time->reset();
-    }
+  // drop all time bins, including those beyond the timeframe limit, so that no MC labels survive
+  for (auto time : mTimeBins) {
+    delete time;
   }
+  mTimeBins.assign(mOffset, nullptr);
   if (mPrevDigArr) {
     std::fill(mPrevDigArr->begin(), mPrevDigArr->end(), PrevDigitInfo{});
   }

Detectors/TPC/simulation/test/CMakeLists.txt

@@ -16,6 +16,13 @@ o2_add_test(DigitContainer
             SOURCES testTPCDigitContainer.cxx
             ENVIRONMENT O2_ROOT=${CMAKE_BINARY_DIR}/stage)
 
+o2_add_test(DigitContainerReset
+            LABELS tpc
+            PUBLIC_LINK_LIBRARIES O2::TPCSimulation
+            COMPONENT_NAME tpc
+            SOURCES testTPCDigitContainerReset.cxx
+            ENVIRONMENT O2_ROOT=${CMAKE_BINARY_DIR}/stage)
+
 o2_add_test(ElectronTransport
             LABELS tpc
             PUBLIC_LINK_LIBRARIES O2::TPCSimulation

Detectors/TPC/simulation/test/testTPCDigitContainerReset.cxx

@@ -0,0 +1,70 @@
+// Copyright 2019-2020 CERN and copyright holders of ALICE O2.
+// See https://alice-o2.web.cern.ch/copyright for details of the copyright holders.
+// All rights not expressly granted are reserved.
+//
+// This software is distributed under the terms of the GNU General Public
+// License v3 (GPL Version 3), copied verbatim in the file "COPYING".
+//
+// In applying this license CERN does not waive the privileges and immunities
+// granted to it by virtue of its status as an Intergovernmental Organization
+// or submit itself to any jurisdiction.
+
+/// \file testTPCDigitContainerReset.cxx
+/// \brief Test that DigitContainer::reset() leaves no MC labels behind for the next sector
+
+#define BOOST_TEST_MODULE Test TPC DigitContainer reset
+#define BOOST_TEST_MAIN
+#define BOOST_TEST_DYN_LINK
+#include <boost/test/unit_test.hpp>
+#include <vector>
+#include <fmt/format.h>
+#include "DataFormatsTPC/Digit.h"
+#include "TPCSimulation/DigitContainer.h"
+#include "TPCSimulation/SAMPAProcessing.h"
+#include "TPCBaseRecSim/CDBInterface.h"
+
+namespace o2::tpc
+{
+
+// A sector whose last time bins lie beyond the timeframe limit must not pass their labels to the next sector
+BOOST_AUTO_TEST_CASE(DigitContainer_noLabelCarryOver)
+{
+  auto& cdb = CDBInterface::instance();
+  cdb.setUseDefaults();
+  // limit the flush to one orbit (time bin 447) and propagate the ADC values unchanged
+  o2::conf::ConfigurableParam::updateFromString(fmt::format("DigiParams.maxOrbitsToDigitize=1;TPCEleParam.DigiMode={}", (int)DigitzationMode::PropagateADC));
+  const Mapper& mapper = Mapper::instance();
+  SAMPAProcessing::instance();
+
+  const GlobalPadNumber globalPad = mapper.getPadNumberInROC(PadROCPos(CRU(0).roc(), PadPos(10, 10)));
+  const MCCompLabel labelFirst(1, 1, 0, false);
+  const MCCompLabel labelSecond(2, 2, 0, false);
+
+  DigitContainer digitContainer;
+  digitContainer.reset();
+
+  // first sector: a signal beyond the timeframe limit, which the final flush does not reach
+  digitContainer.addDigit(labelFirst, CRU(0), 600, globalPad, 100);
+  std::vector<Digit> digits;
+  dataformats::MCTruthContainer<MCCompLabel> labels;
+  std::vector<CommonMode> commonMode;
+  digitContainer.fillOutputContainer(digits, labels, commonMode, Sector(0), 0, true, true);
+  BOOST_CHECK(digits.empty());
+
+  // second sector, as after Digitizer::setSector(): same pad, early time bin
+  digitContainer.reset();
+  digits.clear();
+  labels.clear();
+  commonMode.clear();
+  digitContainer.addDigit(labelSecond, CRU(10), 153, globalPad, 100);
+  digitContainer.fillOutputContainer(digits, labels, commonMode, Sector(1), 0, true, true);
+
+  BOOST_REQUIRE(digits.size() == 1);
+  const auto digitLabels = labels.getLabels(0);
+  BOOST_CHECK_EQUAL(digitLabels.size(), 1);
+  for (const auto& label : digitLabels) {
+    BOOST_CHECK(label == labelSecond);
+  }
+}
+
+} // namespace o2::tpc