fix(Scripts/Spells): defer aura mutations out of proc-check handlers (#26644)

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

src/server/game/Spells/SpellScript.h

@@ -823,12 +823,14 @@ public:
 #define AuraEffectSplitFn(F, I) EffectSplitFunction(&F, I)
 
     // executed when aura checks if it can proc
+    // do not use this hook for triggering spellcasts/removing auras etc - runs mid proc-iteration and may be unsafe
     // example: DoCheckProc += AuraCheckProcFn(class::function);
     // where function is: bool function (ProcEventInfo& eventInfo);
     HookList<CheckProcHandler> DoCheckProc;
 #define AuraCheckProcFn(F) CheckProcHandlerFunction(&F)
 
     // executed when aura effect checks if it can proc the aura
+    // do not use this hook for triggering spellcasts/removing auras etc - runs mid proc-iteration and may be unsafe
     // example: DoCheckEffectProc += AuraCheckEffectProcFn(class::function, EffectIndexSpecifier, EffectAuraNameSpecifier);
     // where function is: bool function (AuraEffect const* aurEff, ProcEventInfo& eventInfo);
     HookList<CheckEffectProcHandler> DoCheckEffectProc;

src/server/scripts/Outland/TempestKeep/botanica/instance_the_botanica.cpp

@@ -127,9 +127,19 @@ class spell_botanica_shift_form_aura : public AuraScript
             {
                 _swapTime = GameTime::GetGameTime().count() + 6;
                 _lastSchool = spellInfo->GetSchoolMask();
-                GetUnitOwner()->RemoveAurasDueToSpell(_lastForm);
+
+                // Runs from Aura::GetProcEffectMask while the proc engine iterates the owner's
+                // applied-aura map. Swapping forms mutates that map (RemoveAura + CastSpell),
+                // which invalidates the live iterator now that aura containers are flat_multimaps.
+                // Defer the swap to the owner's event queue so it runs outside the proc walk.
+                Unit* owner = GetUnitOwner();
+                uint32 const oldForm = _lastForm;
                 _lastForm = form;
-                GetUnitOwner()->CastSpell(GetUnitOwner(), _lastForm, true);
+                owner->m_Events.AddEventAtOffset([owner, oldForm, form]()
+                {
+                    owner->RemoveAurasDueToSpell(oldForm);
+                    owner->CastSpell(owner, form, true);
+                }, 1ms);
             }
         }
 

src/server/scripts/Spells/spell_mage.cpp

@@ -123,16 +123,21 @@ class spell_mage_burning_determination : public AuraScript
         if (!(eventInfo.GetSpellInfo()->GetAllEffectsMechanicMask() & ((1ULL << MECHANIC_INTERRUPT) | (1ULL << MECHANIC_SILENCE))))
             return false;
 
+        Unit* target = eventInfo.GetActionTarget();
+
+        // This hook runs while the proc engine iterates the target's aura map; removing an
+        // aura inline would invalidate the live iterator (aura containers are flat_multimaps).
+        // Defer removals to the target's event queue so they run outside the proc walk.
         // Xinef: immuned effect should just eat charge
         if (eventInfo.GetHitMask() & PROC_EX_IMMUNE)
         {
-            eventInfo.GetActionTarget()->RemoveAurasDueToSpell(54748);
+            target->m_Events.AddEventAtOffset([target]() { target->RemoveAurasDueToSpell(54748); }, 1ms);
             return false;
         }
-        if (Aura* aura = eventInfo.GetActionTarget()->GetAura(54748))
+        if (Aura* aura = target->GetAura(54748))
         {
             if (aura->GetDuration() < aura->GetMaxDuration())
-                eventInfo.GetActionTarget()->RemoveAurasDueToSpell(54748);
+                target->m_Events.AddEventAtOffset([target]() { target->RemoveAurasDueToSpell(54748); }, 1ms);
             return false;
         }
 
@@ -1045,7 +1050,14 @@ class spell_mage_combustion : public AuraScript
         // Do not take charges, add a stack of crit buff
         if (!(eventInfo.GetHitMask() & PROC_HIT_CRITICAL))
         {
-            eventInfo.GetActor()->CastSpell(static_cast<Unit*>(nullptr), SPELL_MAGE_COMBUSTION_PROC, true);
+            // Applying the stack mutates the actor's aura map while the proc engine iterates
+            // it (this hook runs from Aura::GetProcEffectMask); defer it so the insert can't
+            // invalidate the live iterator (aura containers are flat_multimaps).
+            Unit* actor = eventInfo.GetActor();
+            actor->m_Events.AddEventAtOffset([actor]()
+            {
+                actor->CastSpell(static_cast<Unit*>(nullptr), SPELL_MAGE_COMBUSTION_PROC, true);
+            }, 1ms);
             return false;
         }