fix circular module dep: thread trackID counter via pointer instead of include

G4tracking cannot include G4EventManager.hh because G4event already
depends on G4tracking, creating a circular dependency. Fix: pass a
raw G4int* pointer to the event-level trackIDCounter from G4EventManager
through G4TrackingManager::SetTrackIDCounter into G4SteppingManager,
where ProcessSecondariesFromParticleChange uses it to pre-assign track
IDs without any new include.

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

source/event/include/G4EventManager.hh

@@ -59,9 +59,6 @@ class G4EventManager
     static G4EventManager* GetEventManager();
       // This method returns the singleton pointer of G4EventManager.
 
-    G4int ReserveNextTrackID();
-      // Pre-assign the next sequential track ID to a secondary being born inside
-      // G4SteppingManager, so that its ID is available in UserSteppingAction.
 
     G4EventManager();
    ~G4EventManager();

source/event/src/G4EventManager.cc

@@ -172,6 +172,8 @@ void G4EventManager::DoProcessing(G4Event* anEvent,
   }
 #endif
 
+  trackManager->SetTrackIDCounter(&trackIDCounter);
+
   std::unordered_set<G4VTrackingManager *> trackingManagersToFlush;
 
   do
@@ -401,11 +403,6 @@ G4int G4EventManager::StoreSubEvent(G4Event* evt, G4int& subEvtType, G4SubEvent*
   return evt->StoreSubEvent(subEvtType,se);
 }
 
-G4int G4EventManager::ReserveNextTrackID()
-{
-  return ++trackIDCounter;
-}
-
 void G4EventManager::StackTracks(G4TrackVector* trackVector,
                                  G4bool IDhasAlreadySet)
 {

source/tracking/include/G4SteppingManager.hh

@@ -90,6 +90,7 @@ class G4SteppingManager
   void SetUserAction(G4UserSteppingAction* apAction);
   G4Track* GetTrack() const;
   void SetVerboseLevel(G4int vLevel);
+  void SetTrackIDCounter(G4int* counter) { fTrackIDCounter = counter; }
   void SetVerbose(G4VSteppingVerbose*);
   G4Step* GetStep() const;
   void SetNavigator(G4Navigator* value);
@@ -195,6 +196,8 @@ class G4SteppingManager
 
   G4double sumEnergyChange = 0.0;
 
+  G4int* fTrackIDCounter = nullptr; // pointer into G4EventManager::trackIDCounter, set via SetTrackIDCounter
+
   G4VParticleChange* fParticleChange = nullptr;
   G4Track* fTrack = nullptr;
   G4TrackVector* fSecondary = nullptr;

source/tracking/include/G4TrackingManager.hh

@@ -78,6 +78,7 @@ class G4TrackingManager
   void SetStoreTrajectory(G4int value);
 
   G4SteppingManager* GetSteppingManager() const;
+  void SetTrackIDCounter(G4int* counter) { fpSteppingManager->SetTrackIDCounter(counter); }
 
   G4UserTrackingAction* GetUserTrackingAction() const;
 

source/tracking/src/G4SteppingManager.cc

@@ -32,7 +32,6 @@
 // --------------------------------------------------------------------
 
 #include "G4SteppingManager.hh"
-#include "G4EventManager.hh"
 
 #include "G4ForceCondition.hh"
 #include "G4GPILSelection.hh"
@@ -603,7 +602,9 @@ G4int G4SteppingManager::ProcessSecondariesFromParticleChange()
 
     // Pre-assign track ID so it is visible in UserSteppingAction via
     // GetSecondaryInCurrentStep(); G4EventManager::StackTracks skips re-assignment.
-    tempSecondaryTrack->SetTrackID(G4EventManager::GetEventManager()->ReserveNextTrackID());
+    if (fTrackIDCounter) {
+      tempSecondaryTrack->SetTrackID(++(*fTrackIDCounter));
+    }
 
     // If this 2ndry particle has 'zero' kinetic energy, make sure
     // it invokes a rest process at the beginning of the tracking