Add bitmap storage for engine hooks interface

src/Engine.sol

@@ -268,7 +268,9 @@ contract Engine is IEngine, MappingAllocator {
         uint256 numHooks = battle.engineHooks.length;
         if (numHooks > 0) {
             for (uint256 i; i < numHooks;) {
-                config.engineHooks[i] = battle.engineHooks[i];
+                IEngineHook hook = battle.engineHooks[i];
+                config.engineHooks[i].hook = hook;
+                config.engineHooks[i].stepsBitmap = hook.getStepsBitmap();
                 unchecked {
                     ++i;
                 }
@@ -296,8 +298,10 @@ contract Engine is IEngine, MappingAllocator {
             }
         }
 
-        for (uint256 i = 0; i < battle.engineHooks.length;) {
-            battle.engineHooks[i].onBattleStart(battleKey);
+        for (uint256 i = 0; i < numHooks;) {
+            if ((config.engineHooks[i].stepsBitmap & (1 << uint8(EngineHookStep.OnBattleStart))) != 0) {
+                config.engineHooks[i].hook.onBattleStart(battleKey);
+            }
             unchecked {
                 ++i;
             }
@@ -388,7 +392,9 @@ contract Engine is IEngine, MappingAllocator {
 
         uint256 numHooks = config.engineHooksLength;
         for (uint256 i = 0; i < numHooks;) {
-            config.engineHooks[i].onRoundStart(battleKey);
+            if ((config.engineHooks[i].stepsBitmap & (1 << uint8(EngineHookStep.OnRoundStart))) != 0) {
+                config.engineHooks[i].hook.onRoundStart(battleKey);
+            }
             unchecked {
                 ++i;
             }
@@ -590,7 +596,9 @@ contract Engine is IEngine, MappingAllocator {
 
         // Run the round end hooks
         for (uint256 i = 0; i < numHooks;) {
-            config.engineHooks[i].onRoundEnd(battleKey);
+            if ((config.engineHooks[i].stepsBitmap & (1 << uint8(EngineHookStep.OnRoundEnd))) != 0) {
+                config.engineHooks[i].hook.onRoundEnd(battleKey);
+            }
             unchecked {
                 ++i;
             }
@@ -737,7 +745,9 @@ contract Engine is IEngine, MappingAllocator {
         }
 
         for (uint256 i = 0; i < config.engineHooksLength;) {
-            config.engineHooks[i].onBattleEnd(battleKey);
+            if ((config.engineHooks[i].stepsBitmap & (1 << uint8(EngineHookStep.OnBattleEnd))) != 0) {
+                config.engineHooks[i].hook.onBattleEnd(battleKey);
+            }
             unchecked {
                 ++i;
             }

src/Enums.sol

@@ -78,3 +78,10 @@ enum ExtraDataType {
     SelfTeamIndex,
     OpponentNonKOTeamIndex
 }
+
+enum EngineHookStep {
+    OnBattleStart,
+    OnRoundStart,
+    OnRoundEnd,
+    OnBattleEnd
+}

src/IEngineHook.sol

@@ -2,6 +2,10 @@
 pragma solidity ^0.8.0;
 
 interface IEngineHook {
+    // Returns pre-computed bitmap of steps this hook runs at (set at deploy time)
+    // Bit layout: OnBattleStart=0x01, OnRoundStart=0x02, OnRoundEnd=0x04, OnBattleEnd=0x08
+    function getStepsBitmap() external view returns (uint16);
+
     function onBattleStart(bytes32 battleKey) external;
     function onRoundStart(bytes32 battleKey) external;
     function onRoundEnd(bytes32 battleKey) external;

src/Structs.sol

@@ -91,7 +91,7 @@ struct BattleConfig {
     mapping(uint256 => EffectInstance) globalEffects;
     mapping(uint256 => EffectInstance) p0Effects;
     mapping(uint256 => EffectInstance) p1Effects;
-    mapping(uint256 => IEngineHook) engineHooks;
+    mapping(uint256 => EngineHookInstance) engineHooks;
 }
 
 struct EffectInstance {
@@ -101,6 +101,12 @@ struct EffectInstance {
     bytes32 data;         // 256 bits in slot 1
 }
 
+struct EngineHookInstance {
+    IEngineHook hook;     // 160 bits (packed with stepsBitmap in slot 0)
+    uint16 stepsBitmap;   // 16 bits - packs with hook in slot 0 (bit i = runs at EngineHookStep(i))
+    // 80 bits unused in slot 0
+}
+
 // View struct for getBattle - contains array instead of mapping for memory return
 struct BattleConfigView {
     IValidator validator;

src/gacha/GachaRegistry.sol

@@ -15,6 +15,9 @@ import {IMoveSet} from "../moves/IMoveSet.sol";
 contract GachaRegistry is IMonRegistry, IEngineHook, IOwnableMon, IGachaRNG {
     using EnumerableSetLib for EnumerableSetLib.Uint256Set;
 
+    // Only runs at OnBattleEnd (bit 3 = 0x08)
+    uint16 public constant STEPS_BITMAP = 0x08;
+
     uint256 public constant INITIAL_ROLLS = 4;
     uint256 public constant ROLL_COST = 7;
     uint256 public constant POINTS_PER_WIN = 2;
@@ -118,6 +121,10 @@ contract GachaRegistry is IMonRegistry, IEngineHook, IOwnableMon, IGachaRNG {
     }
 
     // IEngineHook implementation
+    function getStepsBitmap() external pure override returns (uint16) {
+        return STEPS_BITMAP;
+    }
+
     function onBattleStart(bytes32 battleKey) external override {}
 
     function onRoundStart(bytes32 battleKey) external override {}

src/hooks/BattleHistory.sol

@@ -11,8 +11,11 @@ import {EnumerableSetLib} from "../lib/EnumerableSetLib.sol";
 contract BattleHistory is IEngineHook {
     using EnumerableSetLib for EnumerableSetLib.AddressSet;
 
+    // Only runs at OnBattleEnd (bit 3 = 0x08)
+    uint16 public constant STEPS_BITMAP = 0x08;
+
     IEngine public immutable engine;
-    
+
     mapping(address => uint256) private _numBattles;
 
     // Mapping from player address to set of all opponents fought
@@ -31,6 +34,10 @@ contract BattleHistory is IEngineHook {
         engine = _engine;
     }
 
+    function getStepsBitmap() external pure override returns (uint16) {
+        return STEPS_BITMAP;
+    }
+
     function onBattleStart(bytes32 battleKey) external {}
 
     function onRoundStart(bytes32 battleKey) external {}