fix(Core/Vehicles): Remove incorrect passenger->vehicle threat redirection (#25719)

Co-authored-by: blinkysc <blinkysc@users.noreply.github.com>
Co-authored-by: Shauren <shauren.trinity@gmail.com>

src/server/game/Combat/ThreatManager.cpp

@@ -206,6 +206,10 @@ void ThreatReference::HeapNotifyDecreased()
             if (tWho->GetSummonerGUID().IsPlayer())
                 return false;
 
+    // accessories are fully treated as components of the parent and cannot have threat
+    if (cWho->HasUnitTypeMask(UNIT_MASK_ACCESSORY))
+        return false;
+
     return true;
 }
 
@@ -396,15 +400,6 @@ void ThreatManager::AddThreat(Unit* target, float amount, SpellInfo const* spell
             return;
     }
 
-    // while riding a vehicle, all threat goes to the vehicle, not the pilot
-    if (Unit* vehicle = target->GetVehicleBase())
-    {
-        AddThreat(vehicle, amount, spell, ignoreModifiers, ignoreRedirects);
-        if (target->HasUnitTypeMask(UNIT_MASK_ACCESSORY)) // accessories are fully treated as components of the parent and cannot have threat
-            return;
-        amount = 0.0f;
-    }
-
     // if we cannot actually have a threat list, we instead just set combat state and avoid creating threat refs altogether
     if (!CanHaveThreatList())
     {

src/server/game/Entities/Vehicle/Vehicle.cpp

@@ -313,7 +313,10 @@ void Vehicle::InstallAccessory(uint32 entry, int8 seatId, bool minion, uint8 typ
     if (TempSummon* accessory = _me->SummonCreature(entry, *_me, TempSummonType(type), summonTime))
     {
         if (minion)
+        {
             accessory->AddUnitTypeMask(UNIT_MASK_ACCESSORY);
+            accessory->GetThreatMgr().Initialize(); // reinitialize CanHaveThreatList cached value
+        }
 
         if (!_me->HandleSpellClick(accessory, seatId))
         {
@@ -455,9 +458,9 @@ bool Vehicle::AddPassenger(Unit* unit, int8 seatId)
         init.SetTransportEnter();
         init.Launch();
 
-        // Transfer threat from passenger to vehicle
+        // Put the vehicle in combat with anything that was threatening the passenger; the threat itself stays on the passenger
         for (auto const& [guid, threatRef] : unit->GetThreatMgr().GetThreatenedByMeList())
-            threatRef->GetOwner()->GetThreatMgr().AddThreat(_me, threatRef->GetThreat(), nullptr, true, true);
+            threatRef->GetOwner()->GetThreatMgr().AddThreat(_me, 0.0f, nullptr, true, true);
 
         if (_me->IsCreature())
         {