diff --git a/tests/samples/slay-the-spire-like/combat/effects.test.ts b/tests/samples/slay-the-spire-like/combat/effects.test.ts
new file mode 100644
index 0000000..da8ac69
--- /dev/null
+++ b/tests/samples/slay-the-spire-like/combat/effects.test.ts
@@ -0,0 +1,417 @@
+import { describe, it, expect } from 'vitest';
+import {
+    addEffect,
+    addEntityEffect,
+    addItemEffect,
+    onEntityEffectUpkeep,
+    onEntityPostureDamage,
+    onPlayerItemEffectUpkeep,
+    onItemPlay,
+    onItemDiscard,
+    getAliveEnemies,
+    getCombatEntity,
+} from '@/samples/slay-the-spire-like/system/combat/effects';
+import type { CombatEntity, CombatState, EffectTable, PlayerEntity, EnemyEntity } from '@/samples/slay-the-spire-like/system/combat/types';
+import type { EffectData } from '@/samples/slay-the-spire-like/system/types';
+
+function createEffect(id: string, lifecycle: EffectData['lifecycle']): EffectData {
+    return { id, name: id, description: '', lifecycle };
+}
+
+function createCombatEntity(hp = 10, maxHp = 10): CombatEntity {
+    return {
+        effects: {},
+        hp,
+        maxHp,
+        isAlive: hp > 0,
+    };
+}
+
+function createPlayerEntity(hp = 30, maxHp = 30): PlayerEntity {
+    return {
+        ...createCombatEntity(hp, maxHp),
+        energy: 3,
+        maxEnergy: 3,
+        deck: { cards: {}, regions: { drawPile: { id: 'drawPile', axes: [], childIds: [], partMap: {} }, hand: { id: 'hand', axes: [], childIds: [], partMap: {} }, discardPile: { id: 'discardPile', axes: [], childIds: [], partMap: {} }, exhaustPile: { id: 'exhaustPile', axes: [], childIds: [], partMap: {} } } },
+        itemEffects: {},
+    };
+}
+
+function createEnemyEntity(id: string, hp = 10, maxHp = 10): EnemyEntity {
+    return {
+        ...createCombatEntity(hp, maxHp),
+        id,
+        enemy: { id, name: id, description: '' },
+        intents: {},
+        currentIntentId: '',
+    };
+}
+
+function createCombatState(playerHp = 30, enemies: EnemyEntity[] = []): CombatState {
+    return {
+        player: createPlayerEntity(playerHp),
+        enemies,
+        inventory: { width: 6, height: 4, items: new Map(), occupiedCells: new Set() },
+        phase: 'playerTurn',
+        turnNumber: 1,
+        result: null,
+        loot: [],
+    };
+}
+
+describe('combat/effects', () => {
+    describe('addEffect', () => {
+        it('should add a new effect to an empty table', () => {
+            const table: EffectTable = {};
+            const effect = createEffect('strength', 'temporary');
+
+            addEffect(table, effect, 3);
+
+            expect(table['strength']).toBeDefined();
+            expect(table['strength'].data).toBe(effect);
+            expect(table['strength'].stacks).toBe(3);
+        });
+
+        it('should stack with existing effect of same id', () => {
+            const table: EffectTable = {};
+            const effect = createEffect('strength', 'lingering');
+
+            addEffect(table, effect, 2);
+            addEffect(table, effect, 3);
+
+            expect(table['strength'].stacks).toBe(5);
+        });
+
+        it('should remove effect when stacks reach 0', () => {
+            const table: EffectTable = {};
+            const effect = createEffect('strength', 'temporary');
+
+            addEffect(table, effect, 3);
+            addEffect(table, effect, -3);
+
+            expect(table['strength']).toBeUndefined();
+        });
+
+        it('should not add effect when stacks is 0', () => {
+            const table: EffectTable = {};
+            const effect = createEffect('strength', 'temporary');
+
+            addEffect(table, effect, 0);
+
+            expect(table['strength']).toBeUndefined();
+        });
+
+        it('should handle negative stacks', () => {
+            const table: EffectTable = {};
+            const effect = createEffect('weak', 'temporary');
+
+            addEffect(table, effect, -2);
+
+            expect(table['weak'].stacks).toBe(-2);
+        });
+    });
+
+    describe('addEntityEffect', () => {
+        it('should add effect to entity.effects', () => {
+            const entity = createCombatEntity();
+            const effect = createEffect('vulnerable', 'lingering');
+
+            addEntityEffect(entity, effect, 2);
+
+            expect(entity.effects['vulnerable'].stacks).toBe(2);
+        });
+    });
+
+    describe('addItemEffect', () => {
+        it('should add effect to player.itemEffects[itemKey]', () => {
+            const player = createPlayerEntity();
+            const effect = createEffect('adjacent-buff', 'itemTemporary');
+
+            addItemEffect(player, 'sword-1', effect, 3);
+
+            expect(player.itemEffects['sword-1']['adjacent-buff'].stacks).toBe(3);
+        });
+
+        it('should initialize itemEffects entry if not present', () => {
+            const player = createPlayerEntity();
+            const effect = createEffect('adjacent-buff', 'itemTemporary');
+
+            addItemEffect(player, 'new-item', effect, 1);
+
+            expect(player.itemEffects['new-item']).toBeDefined();
+        });
+
+        it('should stack with existing item effect', () => {
+            const player = createPlayerEntity();
+            const effect = createEffect('adjacent-buff', 'itemTemporary');
+
+            addItemEffect(player, 'sword-1', effect, 2);
+            addItemEffect(player, 'sword-1', effect, 3);
+
+            expect(player.itemEffects['sword-1']['adjacent-buff'].stacks).toBe(5);
+        });
+    });
+
+    describe('onEntityEffectUpkeep', () => {
+        it('should remove temporary effects', () => {
+            const entity = createCombatEntity();
+            const tempEffect = createEffect('temp-shield', 'temporary');
+
+            addEntityEffect(entity, tempEffect, 5);
+            onEntityEffectUpkeep(entity);
+
+            expect(entity.effects['temp-shield']).toBeUndefined();
+        });
+
+        it('should decrement lingering effects by 1', () => {
+            const entity = createCombatEntity();
+            const lingeringEffect = createEffect('poison', 'lingering');
+
+            addEntityEffect(entity, lingeringEffect, 3);
+            onEntityEffectUpkeep(entity);
+
+            expect(entity.effects['poison'].stacks).toBe(2);
+        });
+
+        it('should remove lingering effects when stacks reach 0', () => {
+            const entity = createCombatEntity();
+            const lingeringEffect = createEffect('poison', 'lingering');
+
+            addEntityEffect(entity, lingeringEffect, 1);
+            onEntityEffectUpkeep(entity);
+
+            expect(entity.effects['poison']).toBeUndefined();
+        });
+
+        it('should not affect permanent effects', () => {
+            const entity = createCombatEntity();
+            const permEffect = createEffect('max-hp-up', 'permanent');
+
+            addEntityEffect(entity, permEffect, 5);
+            onEntityEffectUpkeep(entity);
+
+            expect(entity.effects['max-hp-up'].stacks).toBe(5);
+        });
+
+        it('should not affect instant effects', () => {
+            const entity = createCombatEntity();
+            const instantEffect = createEffect('instant-damage', 'instant');
+
+            addEntityEffect(entity, instantEffect, 10);
+            onEntityEffectUpkeep(entity);
+
+            expect(entity.effects['instant-damage'].stacks).toBe(10);
+        });
+
+        it('should increment lingering effects with negative stacks', () => {
+            const entity = createCombatEntity();
+            const lingeringEffect = createEffect('regen', 'lingering');
+
+            addEntityEffect(entity, lingeringEffect, -3);
+            onEntityEffectUpkeep(entity);
+
+            expect(entity.effects['regen'].stacks).toBe(-2);
+        });
+    });
+
+    describe('onEntityPostureDamage', () => {
+        it('should reduce posture effects by damage amount', () => {
+            const entity = createCombatEntity();
+            const postureEffect = createEffect('block', 'posture');
+
+            addEntityEffect(entity, postureEffect, 10);
+            onEntityPostureDamage(entity, 4);
+
+            expect(entity.effects['block'].stacks).toBe(6);
+        });
+
+        it('should not reduce posture effects below 0', () => {
+            const entity = createCombatEntity();
+            const postureEffect = createEffect('block', 'posture');
+
+            addEntityEffect(entity, postureEffect, 3);
+            onEntityPostureDamage(entity, 10);
+
+            expect(entity.effects['block']).toBeUndefined();
+        });
+
+        it('should not affect non-posture effects', () => {
+            const entity = createCombatEntity();
+            const postureEffect = createEffect('block', 'posture');
+            const permEffect = createEffect('strength', 'permanent');
+
+            addEntityEffect(entity, postureEffect, 5);
+            addEntityEffect(entity, permEffect, 3);
+            onEntityPostureDamage(entity, 2);
+
+            expect(entity.effects['block'].stacks).toBe(3);
+            expect(entity.effects['strength'].stacks).toBe(3);
+        });
+
+        it('should handle zero damage', () => {
+            const entity = createCombatEntity();
+            const postureEffect = createEffect('block', 'posture');
+
+            addEntityEffect(entity, postureEffect, 5);
+            onEntityPostureDamage(entity, 0);
+
+            expect(entity.effects['block'].stacks).toBe(5);
+        });
+    });
+
+    describe('onPlayerItemEffectUpkeep', () => {
+        it('should remove itemTemporary effects', () => {
+            const player = createPlayerEntity();
+            const effect = createEffect('adjacent-buff', 'itemTemporary');
+
+            addItemEffect(player, 'sword-1', effect, 5);
+            onPlayerItemEffectUpkeep(player);
+
+            expect(player.itemEffects['sword-1']['adjacent-buff']).toBeUndefined();
+        });
+
+        it('should not affect itemPermanent effects', () => {
+            const player = createPlayerEntity();
+            const effect = createEffect('adjacent-buff', 'itemPermanent');
+
+            addItemEffect(player, 'sword-1', effect, 5);
+            onPlayerItemEffectUpkeep(player);
+
+            expect(player.itemEffects['sword-1']['adjacent-buff'].stacks).toBe(5);
+        });
+
+        it('should not affect itemUntilPlay effects', () => {
+            const player = createPlayerEntity();
+            const effect = createEffect('charged', 'itemUntilPlay');
+
+            addItemEffect(player, 'sword-1', effect, 3);
+            onPlayerItemEffectUpkeep(player);
+
+            expect(player.itemEffects['sword-1']['charged'].stacks).toBe(3);
+        });
+    });
+
+    describe('onItemPlay', () => {
+        it('should remove itemUntilPlay effects', () => {
+            const player = createPlayerEntity();
+            const effect = createEffect('charged', 'itemUntilPlay');
+
+            addItemEffect(player, 'sword-1', effect, 3);
+            onItemPlay(player, 'sword-1');
+
+            expect(player.itemEffects['sword-1']['charged']).toBeUndefined();
+        });
+
+        it('should not affect other lifecycle effects', () => {
+            const player = createPlayerEntity();
+            const permEffect = createEffect('passive', 'itemPermanent');
+            const playEffect = createEffect('charged', 'itemUntilPlay');
+
+            addItemEffect(player, 'sword-1', permEffect, 5);
+            addItemEffect(player, 'sword-1', playEffect, 3);
+            onItemPlay(player, 'sword-1');
+
+            expect(player.itemEffects['sword-1']['passive'].stacks).toBe(5);
+            expect(player.itemEffects['sword-1']['charged']).toBeUndefined();
+        });
+
+        it('should do nothing for item with no effects', () => {
+            const player = createPlayerEntity();
+
+            expect(() => onItemPlay(player, 'nonexistent')).not.toThrow();
+        });
+    });
+
+    describe('onItemDiscard', () => {
+        it('should remove itemUntilDiscard effects', () => {
+            const player = createPlayerEntity();
+            const effect = createEffect('discard-buff', 'itemUntilDiscard');
+
+            addItemEffect(player, 'sword-1', effect, 3);
+            onItemDiscard(player, 'sword-1');
+
+            expect(player.itemEffects['sword-1']['discard-buff']).toBeUndefined();
+        });
+
+        it('should not affect other lifecycle effects', () => {
+            const player = createPlayerEntity();
+            const permEffect = createEffect('passive', 'itemPermanent');
+            const discardEffect = createEffect('discard-buff', 'itemUntilDiscard');
+
+            addItemEffect(player, 'sword-1', permEffect, 5);
+            addItemEffect(player, 'sword-1', discardEffect, 3);
+            onItemDiscard(player, 'sword-1');
+
+            expect(player.itemEffects['sword-1']['passive'].stacks).toBe(5);
+            expect(player.itemEffects['sword-1']['discard-buff']).toBeUndefined();
+        });
+
+        it('should do nothing for item with no effects', () => {
+            const player = createPlayerEntity();
+
+            expect(() => onItemDiscard(player, 'nonexistent')).not.toThrow();
+        });
+    });
+
+    describe('getAliveEnemies', () => {
+        it('should yield only alive enemies', () => {
+            const state = createCombatState(30, [
+                createEnemyEntity('slime-1', 10, 10),
+                createEnemyEntity('slime-2', 0, 10),
+                createEnemyEntity('slime-3', 5, 10),
+            ]);
+
+            const alive = [...getAliveEnemies(state)];
+
+            expect(alive.length).toBe(2);
+            expect(alive[0].id).toBe('slime-1');
+            expect(alive[1].id).toBe('slime-3');
+        });
+
+        it('should return empty for no enemies', () => {
+            const state = createCombatState(30, []);
+
+            const alive = [...getAliveEnemies(state)];
+
+            expect(alive.length).toBe(0);
+        });
+
+        it('should return empty when all enemies are dead', () => {
+            const state = createCombatState(30, [
+                createEnemyEntity('slime-1', 0, 10),
+                createEnemyEntity('slime-2', 0, 10),
+            ]);
+
+            const alive = [...getAliveEnemies(state)];
+
+            expect(alive.length).toBe(0);
+        });
+    });
+
+    describe('getCombatEntity', () => {
+        it('should return player for "player" key', () => {
+            const state = createCombatState(30);
+
+            const entity = getCombatEntity(state, 'player');
+
+            expect(entity).toBe(state.player);
+        });
+
+        it('should return enemy by id', () => {
+            const enemy = createEnemyEntity('boss-1', 50, 50);
+            const state = createCombatState(30, [enemy]);
+
+            const entity = getCombatEntity(state, 'boss-1');
+
+            expect(entity).toBe(enemy);
+        });
+
+        it('should return undefined for non-existent enemy', () => {
+            const state = createCombatState(30, [createEnemyEntity('slime-1')]);
+
+            const entity = getCombatEntity(state, 'nonexistent');
+
+            expect(entity).toBeUndefined();
+        });
+    });
+});
diff --git a/tests/utils/middleware.test.ts b/tests/utils/middleware.test.ts
new file mode 100644
index 0000000..d775d80
--- /dev/null
+++ b/tests/utils/middleware.test.ts
@@ -0,0 +1,436 @@
+import { describe, it, expect } from 'vitest';
+import { createMiddlewareChain, type MiddlewareChain } from '@/utils/middleware';
+
+describe('createMiddlewareChain', () => {
+    describe('basic execution', () => {
+        it('should return context when no middlewares and no fallback', async () => {
+            const chain = createMiddlewareChain<{ value: number }>();
+            const result = await chain.execute({ value: 42 });
+
+            expect(result).toEqual({ value: 42 });
+        });
+
+        it('should call fallback when no middlewares', async () => {
+            const chain = createMiddlewareChain<{ value: number }, string>(
+                async ctx => `value is ${ctx.value}`
+            );
+            const result = await chain.execute({ value: 42 });
+
+            expect(result).toBe('value is 42');
+        });
+
+        it('should pass context to fallback', async () => {
+            const chain = createMiddlewareChain<{ a: number; b: number }, number>(
+                async ctx => ctx.a + ctx.b
+            );
+            const result = await chain.execute({ a: 3, b: 7 });
+
+            expect(result).toBe(10);
+        });
+    });
+
+    describe('single middleware', () => {
+        it('should execute a single middleware', async () => {
+            const chain = createMiddlewareChain<{ count: number }>();
+            chain.use(async (ctx, next) => {
+                ctx.count *= 2;
+                return next();
+            });
+
+            const result = await chain.execute({ count: 5 });
+
+            expect(result.count).toBe(10);
+        });
+
+        it('should allow middleware to modify return value', async () => {
+            const chain = createMiddlewareChain<{ value: number }, number>(
+                async ctx => ctx.value
+            );
+            chain.use(async (ctx, next) => {
+                const result = await next();
+                return result * 2;
+            });
+
+            const result = await chain.execute({ value: 21 });
+
+            expect(result).toBe(42);
+        });
+
+        it('should allow middleware to short-circuit without calling next', async () => {
+            const chain = createMiddlewareChain<{ value: number }>();
+            chain.use(async (_ctx, _next) => {
+                return { value: 999 };
+            });
+
+            const result = await chain.execute({ value: 1 });
+
+            expect(result.value).toBe(999);
+        });
+    });
+
+    describe('multiple middlewares', () => {
+        it('should execute middlewares in order', async () => {
+            const order: number[] = [];
+            const chain = createMiddlewareChain<{ value: number }>();
+
+            chain.use(async (_ctx, next) => {
+                order.push(1);
+                const result = await next();
+                order.push(4);
+                return result;
+            });
+            chain.use(async (_ctx, next) => {
+                order.push(2);
+                const result = await next();
+                order.push(3);
+                return result;
+            });
+
+            await chain.execute({ value: 0 });
+
+            expect(order).toEqual([1, 2, 3, 4]);
+        });
+
+        it('should accumulate modifications through the chain', async () => {
+            const chain = createMiddlewareChain<{ value: number }>();
+
+            chain.use(async (ctx, next) => {
+                ctx.value += 1;
+                return next();
+            });
+            chain.use(async (ctx, next) => {
+                ctx.value *= 2;
+                return next();
+            });
+            chain.use(async (ctx, next) => {
+                ctx.value += 3;
+                return next();
+            });
+
+            const result = await chain.execute({ value: 0 });
+
+            expect(result.value).toBe(5);
+        });
+
+        it('should allow middleware to modify result on the way back', async () => {
+            const chain = createMiddlewareChain<{ base: number }, number>(
+                async ctx => ctx.base
+            );
+
+            chain.use(async (_ctx, next) => {
+                const result = await next();
+                return result + 10;
+            });
+            chain.use(async (_ctx, next) => {
+                const result = await next();
+                return result * 2;
+            });
+
+            const result = await chain.execute({ base: 5 });
+
+            expect(result).toBe(20);
+        });
+
+        it('should allow middleware to short-circuit in the middle', async () => {
+            const executed: number[] = [];
+            const chain = createMiddlewareChain<{ value: number }>();
+
+            chain.use(async (_ctx, next) => {
+                executed.push(1);
+                return next();
+            });
+            chain.use(async () => {
+                executed.push(2);
+                return { value: -1 };
+            });
+            chain.use(async (_ctx, next) => {
+                executed.push(3);
+                return next();
+            });
+
+            const result = await chain.execute({ value: 100 });
+
+            expect(result.value).toBe(-1);
+            expect(executed).toEqual([1, 2]);
+        });
+    });
+
+    describe('nested next calls', () => {
+        it('should advance index on each next call, skipping remaining middlewares', async () => {
+            const chain = createMiddlewareChain<{ counter: number }>();
+
+            chain.use(async (_ctx, next) => {
+                await next();
+                await next();
+            });
+
+            const result = await chain.execute({ counter: 0 });
+
+            expect(result).toBeUndefined();
+        });
+
+        it('should allow middleware to call next conditionally', async () => {
+            const chain = createMiddlewareChain<{ skip: boolean; value: number }>();
+
+            chain.use(async (ctx, next) => {
+                if (ctx.skip) {
+                    return { value: -1 };
+                }
+                return next();
+            });
+            chain.use(async (ctx, next) => {
+                ctx.value += 10;
+                return next();
+            });
+
+            const resultA = await chain.execute({ skip: true, value: 0 });
+            const resultB = await chain.execute({ skip: false, value: 0 });
+
+            expect(resultA.value).toBe(-1);
+            expect(resultB.value).toBe(10);
+        });
+
+        it('should handle middleware that awaits next multiple times with a fallback', async () => {
+            const log: string[] = [];
+            const chain = createMiddlewareChain<{ value: number }, string[]>(
+                async _ctx => log
+            );
+
+            chain.use(async (_ctx, next) => {
+                log.push('before');
+                await next();
+                log.push('after-first');
+                await next();
+                log.push('after-second');
+                return log;
+            });
+            chain.use(async (_ctx, next) => {
+                log.push('mw2');
+                return next();
+            });
+
+            const result = await chain.execute({ value: 0 });
+
+            expect(result).toEqual(['before', 'mw2', 'after-first', 'after-second']);
+        });
+
+        it('should return fallback result on second next call when no more middlewares remain', async () => {
+            const chain = createMiddlewareChain<{ value: number }, number>(
+                async ctx => ctx.value * 10
+            );
+
+            chain.use(async (_ctx, next) => {
+                await next();
+                return await next();
+            });
+            chain.use(async (_ctx, next) => {
+                return next();
+            });
+
+            const result = await chain.execute({ value: 5 });
+
+            expect(result).toBe(50);
+        });
+
+        it('should return fallback result on second next call when no more middlewares remain', async () => {
+            const chain = createMiddlewareChain<{ value: number }, number>(
+                async ctx => ctx.value * 10
+            );
+
+            chain.use(async (_ctx, next) => {
+                await next();
+                return await next();
+            });
+            chain.use(async (_ctx, next) => {
+                return next();
+            });
+
+            const result = await chain.execute({ value: 5 });
+
+            expect(result).toBe(50);
+        });
+    });
+
+    describe('async behavior', () => {
+        it('should handle async middlewares', async () => {
+            const chain = createMiddlewareChain<{ value: number }>();
+
+            chain.use(async (ctx, next) => {
+                await new Promise(resolve => setTimeout(resolve, 10));
+                ctx.value += 1;
+                return next();
+            });
+            chain.use(async (ctx, next) => {
+                await new Promise(resolve => setTimeout(resolve, 10));
+                ctx.value += 2;
+                return next();
+            });
+
+            const result = await chain.execute({ value: 0 });
+
+            expect(result.value).toBe(3);
+        });
+
+        it('should handle async fallback', async () => {
+            const chain = createMiddlewareChain<{ value: number }, number>(
+                async ctx => {
+                    await new Promise(resolve => setTimeout(resolve, 10));
+                    return ctx.value * 10;
+                }
+            );
+
+            const result = await chain.execute({ value: 5 });
+
+            expect(result).toBe(50);
+        });
+    });
+
+    describe('error handling', () => {
+        it('should propagate errors from middleware', async () => {
+            const chain = createMiddlewareChain<{ value: number }>();
+
+            chain.use(async () => {
+                throw new Error('middleware error');
+            });
+
+            await expect(chain.execute({ value: 1 })).rejects.toThrow('middleware error');
+        });
+
+        it('should propagate errors from fallback', async () => {
+            const chain = createMiddlewareChain<{ value: number }, number>(
+                async () => {
+                    throw new Error('fallback error');
+                }
+            );
+
+            await expect(chain.execute({ value: 1 })).rejects.toThrow('fallback error');
+        });
+
+        it('should allow middleware to catch errors from downstream', async () => {
+            const chain = createMiddlewareChain<{ value: number }>();
+
+            chain.use(async (_ctx, next) => {
+                try {
+                    return await next();
+                } catch {
+                    return { value: -1 };
+                }
+            });
+            chain.use(async () => {
+                throw new Error('downstream error');
+            });
+
+            const result = await chain.execute({ value: 1 });
+
+            expect(result.value).toBe(-1);
+        });
+    });
+
+    describe('return type override', () => {
+        it('should support different TReturn type than TContext', async () => {
+            const chain = createMiddlewareChain<{ name: string }, string>(
+                async ctx => `Hello, ${ctx.name}!`
+            );
+
+            const result = await chain.execute({ name: 'World' });
+
+            expect(result).toBe('Hello, World!');
+        });
+
+        it('should allow middleware to transform return type', async () => {
+            const chain = createMiddlewareChain<{ items: number[] }, number>(
+                async ctx => ctx.items.reduce((a, b) => a + b, 0)
+            );
+
+            chain.use(async (_ctx, next) => {
+                const sum = await next();
+                return sum * 2;
+            });
+
+            const result = await chain.execute({ items: [1, 2, 3] });
+
+            expect(result).toBe(12);
+        });
+    });
+
+    describe('reusability', () => {
+        it('should reset index on each execute call', async () => {
+            const chain = createMiddlewareChain<{ count: number }>();
+
+            chain.use(async (ctx, next) => {
+                ctx.count += 1;
+                return next();
+            });
+
+            const resultA = await chain.execute({ count: 0 });
+            const resultB = await chain.execute({ count: 0 });
+
+            expect(resultA.count).toBe(1);
+            expect(resultB.count).toBe(1);
+        });
+
+        it('should share middlewares across execute calls', async () => {
+            const chain = createMiddlewareChain<{ log: string[] }>();
+
+            chain.use(async (ctx, next) => {
+                ctx.log.push('always');
+                return next();
+            });
+
+            await chain.execute({ log: [] });
+            await chain.execute({ log: [] });
+
+            expect(chain).toBeDefined();
+        });
+    });
+
+    describe('edge cases', () => {
+        it('should handle empty context object', async () => {
+            const chain = createMiddlewareChain<Record<string, never>>();
+            const result = await chain.execute({});
+
+            expect(result).toEqual({});
+        });
+
+        it('should handle middleware that returns a completely different object', async () => {
+            const chain = createMiddlewareChain<{ x: number }, { y: string }>(
+                async () => ({ y: 'default' })
+            );
+
+            chain.use(async (_ctx, next) => {
+                return next();
+            });
+
+            const result = await chain.execute({ x: 42 });
+
+            expect(result).toEqual({ y: 'default' });
+        });
+
+        it('should handle middleware that mutates context without returning', async () => {
+            const chain = createMiddlewareChain<{ value: number }>(
+                async ctx => ctx
+            );
+
+            chain.use(async (ctx, next) => {
+                ctx.value = 100;
+                return next();
+            });
+
+            const result = await chain.execute({ value: 0 });
+
+            expect(result.value).toBe(100);
+        });
+
+        it('should return undefined when middleware does not call next or return', async () => {
+            const chain = createMiddlewareChain<{ value: number }>();
+
+            chain.use(async (ctx) => {
+                ctx.value = 100;
+            });
+
+            const result = await chain.execute({ value: 0 });
+
+            expect(result).toBeUndefined();
+        });
+    });
+});