fix(Scripts/MagtheridonsLair): prevent Hellfire Channelers from respawning during boss fight

data/sql/updates/pending_db_world/rev_1777182648846009000.sql

@@ -0,0 +1,15 @@
+--
+-- Magtheridon's Lair: notify the instance script when a Hellfire Channeler
+-- evades, so the encounter can transition back to NOT_STARTED if the raid
+-- wiped during phase 1 (otherwise the room doors would stay locked).
+--
+DELETE FROM `smart_scripts` WHERE `entryorguid`=17256 AND `source_type`=0 AND `id`=9;
+INSERT INTO `smart_scripts`
+(`entryorguid`,`source_type`,`id`,`link`,`event_type`,`event_phase_mask`,`event_chance`,`event_flags`,
+ `event_param1`,`event_param2`,`event_param3`,`event_param4`,`event_param5`,
+ `action_type`,`action_param1`,`action_param2`,`action_param3`,`action_param4`,`action_param5`,`action_param6`,
+ `target_type`,`target_param1`,`target_param2`,`target_param3`,`target_param4`,
+ `target_x`,`target_y`,`target_z`,`target_o`,`comment`)
+VALUES
+(17256, 0, 9, 0, 7, 0, 100, 0, 0, 0, 0, 0, 0, 34, 10, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0,
+ 'Hellfire Channeler - On Evade - Set Instance Data 10 to 0');

src/server/scripts/Outland/HellfireCitadel/MagtheridonsLair/instance_magtheridons_lair.cpp

@@ -164,9 +164,55 @@ class instance_magtheridons_lair : public InstanceMapScript
             switch (type)
             {
                 case DATA_CHANNELER_COMBAT:
-                    if (GetBossState(DATA_MAGTHERIDON) != IN_PROGRESS)
-                        if (Creature* magtheridon = instance->GetCreature(_magtheridonGUID))
-                            magtheridon->SetInCombatWithZone();
+                    // data == 1: a Channeler entered combat
+                    // data == 0: a Channeler evaded (sent from C++ on JustReachedHome)
+                    if (data == 1)
+                    {
+                        if (GetBossState(DATA_MAGTHERIDON) != IN_PROGRESS)
+                        {
+                            // Force the encounter into IN_PROGRESS as soon as any Channeler
+                            // is engaged. This:
+                            //   1) closes the room doors and notifies boss mods (DBM, etc.)
+                            //   2) prevents dead Channelers from being resurrected later by
+                            //      InstanceScript::UpdateMinionState() when Magtheridon's
+                            //      own JustEngagedWith would otherwise transition the state
+                            //      to IN_PROGRESS after the Channelers are dead.
+                            SetBossState(DATA_MAGTHERIDON, IN_PROGRESS);
+                            if (Creature* magtheridon = instance->GetCreature(_magtheridonGUID))
+                                magtheridon->SetInCombatWithZone();
+                        }
+                    }
+                    else // data == 0: Channeler evaded
+                    {
+                        // If we forced the encounter to IN_PROGRESS during phase 1 and the raid
+                        // wiped (or left the room) before Magtheridon was released, Magtheridon
+                        // himself is still passive and will never trigger _EnterEvadeMode to
+                        // reset the state. We must do it manually when all Channelers have
+                        // returned home, otherwise the room doors stay locked forever.
+                        if (GetBossState(DATA_MAGTHERIDON) == IN_PROGRESS)
+                        {
+                            bool anyChannelerStillFighting = false;
+                            DoForAllMinions(DATA_MAGTHERIDON, [&](Creature* channeler)
+                            {
+                                if (channeler->IsAlive() && channeler->IsInCombat())
+                                    anyChannelerStillFighting = true;
+                            });
+
+                            if (!anyChannelerStillFighting)
+                            {
+                                if (Creature* magtheridon = instance->GetCreature(_magtheridonGUID))
+                                {
+                                    // Only reset if Magtheridon is still in his pre-release passive state.
+                                    // If he is already engaged (phase 2/3), his own BossAI handles evade.
+                                    if (!magtheridon->IsEngaged() && magtheridon->IsImmuneToPC())
+                                    {
+                                        SetBossState(DATA_MAGTHERIDON, NOT_STARTED);
+                                        magtheridon->AI()->Reset();
+                                    }
+                                }
+                            }
+                        }
+                    }
                     break;
                 case DATA_ACTIVATE_CUBES:
                     for (ObjectGuid const& guid : _cubesSet)