diff --git a/src/core/game.ts b/src/core/game.ts
index 35b1e31..5d07ef5 100644
--- a/src/core/game.ts
+++ b/src/core/game.ts
@@ -1,23 +1,22 @@
-import {createEntityCollection} from "../utils/entity";
+import {createEntityCollection, entity, Entity, EntityCollection} from "../utils/entity";
 import {Part} from "./part";
 import {Region} from "./region";
 import {
     Command,
     CommandRegistry,
     type CommandRunner, CommandRunnerContext,
-    CommandRunnerContextExport, CommandSchema,
+    CommandRunnerContextExport, CommandSchema, createCommandRegistry,
     createCommandRunnerContext, parseCommandSchema,
     PromptEvent
 } from "../utils/command";
 import {AsyncQueue} from "../utils/async-queue";
-import {signal, Signal} from "@preact/signals-core";
 
 export interface IGameContext<TState extends Record<string, unknown> = {} > {
-    parts: ReturnType<typeof createEntityCollection<Part>>;
-    regions: ReturnType<typeof createEntityCollection<Region>>;
+    parts: EntityCollection<Part>;
+    regions: EntityCollection<Region>;
+    state: Entity<TState>;
     commands: CommandRunnerContextExport<IGameContext<TState>>;
     prompts: AsyncQueue<PromptEvent>;
-    state: Signal<TState>
 }
 
 export function createGameContext<TState extends Record<string, unknown> = {} >(
@@ -27,14 +26,14 @@ export function createGameContext<TState extends Record<string, unknown> = {} >(
     const parts = createEntityCollection<Part>();
     const regions = createEntityCollection<Region>();
     const prompts = new AsyncQueue<PromptEvent>();
-    const state: TState = typeof initialState === 'function' ? (initialState as (() => TState))() : (initialState ?? {} as TState);
+    const state = typeof initialState === 'function' ? initialState() : initialState ?? {} as TState;
 
     const ctx = {
         parts,
         regions,
         prompts,
         commands: null!,
-        state: signal(state),
+        state: entity('gameState', state),
     } as IGameContext<TState>
 
     ctx.commands = createCommandRunnerContext(commandRegistry, ctx);
@@ -56,6 +55,11 @@ export function createGameContextFromModule<TState extends Record<string, unknow
     return createGameContext(module.registry, module.createInitialState);
 }
 
+export function createGameCommandRegistry<TState extends Record<string, unknown> = {} >(): CommandRegistry<IGameContext<TState>> {
+    return createCommandRegistry<IGameContext<TState>>();
+}
+</TState>
+
 export function createGameCommand<TState extends Record<string, unknown> = {} , TResult = unknown>(
     schema: CommandSchema | string,
     run: (this: CommandRunnerContext<IGameContext<TState>>, command: Command) => Promise<TResult>
diff --git a/src/core/part.ts b/src/core/part.ts
index f0b64db..5638577 100644
--- a/src/core/part.ts
+++ b/src/core/part.ts
@@ -1,33 +1,31 @@
-import {Entity, EntityAccessor} from "../utils/entity";
+import {Entity} from "../utils/entity";
 import {Region} from "./region";
 import {RNG} from "../utils/rng";
 
-export type Part = Entity & {
-  // cards have 2 sides, dices have multiple, tokens have 1
+export type Part = {
+  id: string;
   sides: number;
-  
-  // mostly rotations, if relevant
   alignments?: string[];
-
-  // current side
   side: number;
-  // current alignment
   alignment?: string;
-
-  // current region
-  region: EntityAccessor<Region>;
-  // current position in region, expect to be the same length as region's axes
+  region: Entity<Region>;
   position: number[];
 }
 
-export function flip(part: Part) {
-  part.side = (part.side + 1) % part.sides;
+export function flip(part: Entity<Part>) {
+  part.produce(draft => {
+    draft.side = (draft.side + 1) % draft.sides;
+  });
 }
 
-export function flipTo(part: Part, side: number) {
-  part.side = side;
+export function flipTo(part: Entity<Part>, side: number) {
+  part.produce(draft => {
+    draft.side = side;
+  });
 }
 
-export function roll(part: Part, rng: RNG) {
-  part.side = rng.nextInt(part.sides);
+export function roll(part: Entity<Part>, rng: RNG) {
+  part.produce(draft => {
+    draft.side = rng.nextInt(draft.sides);
+  });
 }
diff --git a/src/core/region.ts b/src/core/region.ts
index 5205aac..43c1f22 100644
--- a/src/core/region.ts
+++ b/src/core/region.ts
@@ -1,13 +1,11 @@
-import {Entity, EntityAccessor} from "../utils/entity";
+import {Entity} from "../utils/entity";
 import {Part} from "./part";
 import {RNG} from "../utils/rng";
 
-export type Region = Entity & {
-  // aligning axes of the region, expect a part's position to have a matching number of elements
+export type Region = {
+  id: string;
   axes: RegionAxis[];
-
-  // current children; expect no overlapped positions
-  children: EntityAccessor<Part>[];
+  children: Entity<Part>[];
 }
 
 export type RegionAxis = {
@@ -17,47 +15,35 @@ export type RegionAxis = {
   align?: 'start' | 'end' | 'center';
 }
 
-/**
- * for each axis, try to remove gaps in positions.
- * - if min exists and align is start, and there are parts at (for example) min+2 and min+4, then move them to min and min+1
- * - if max exists and align is end, and there are parts at (for example) max-2 and max-4, then move them to max-1 and max-3
- * - for center, move parts to the center, possibly creating parts placed at 0.5 positions
- * - sort children so that they're in ascending order on each axes.
- * @param region
- */
-export function applyAlign(region: Region){
+export function applyAlign(region: Entity<Region>) {
+  region.produce(applyAlignCore);
+}
+
+function applyAlignCore(region: Region) {
   if (region.children.length === 0) return;
 
-  // Process each axis independently while preserving spatial relationships
   for (let axisIndex = 0; axisIndex < region.axes.length; axisIndex++) {
     const axis = region.axes[axisIndex];
     if (!axis.align) continue;
 
-    // Collect all unique position values on this axis, preserving original order
     const positionValues = new Set<number>();
-    for (const accessor of region.children) {
-      positionValues.add(accessor.value.position[axisIndex] ?? 0);
+    for (const child of region.children) {
+      positionValues.add(child.value.position[axisIndex] ?? 0);
     }
 
-    // Sort position values
     const sortedPositions = Array.from(positionValues).sort((a, b) => a - b);
-
-    // Create position mapping: old position -> new position
     const positionMap = new Map<number, number>();
 
     if (axis.align === 'start' && axis.min !== undefined) {
-      // Compact from min, preserving relative order
       sortedPositions.forEach((pos, index) => {
         positionMap.set(pos, axis.min! + index);
       });
     } else if (axis.align === 'end' && axis.max !== undefined) {
-      // Compact towards max
       const count = sortedPositions.length;
       sortedPositions.forEach((pos, index) => {
         positionMap.set(pos, axis.max! - (count - 1 - index));
       });
     } else if (axis.align === 'center') {
-      // Center alignment
       const count = sortedPositions.length;
       const min = axis.min ?? 0;
       const max = axis.max ?? count - 1;
@@ -70,14 +56,14 @@ export function applyAlign(region: Region){
       });
     }
 
-    // Apply position mapping to all parts
-    for (const accessor of region.children) {
-      const currentPos = accessor.value.position[axisIndex] ?? 0;
-      accessor.value.position[axisIndex] = positionMap.get(currentPos) ?? currentPos;
+    for (const child of region.children) {
+      child.produce(draft => {
+        const currentPos = draft.position[axisIndex] ?? 0;
+        draft.position[axisIndex] = positionMap.get(currentPos) ?? currentPos;
+      });
     }
   }
 
-  // Sort children by all axes at the end
   region.children.sort((a, b) => {
     for (let i = 0; i < region.axes.length; i++) {
       const diff = (a.value.position[i] ?? 0) - (b.value.position[i] ?? 0);
@@ -87,21 +73,23 @@ export function applyAlign(region: Region){
   });
 }
 
-/**
- * shuffle on each axis. for each axis, try to swap position.
- * @param region
- * @param rng
- */
-export function shuffle(region: Region, rng: RNG){
+export function shuffle(region: Entity<Region>, rng: RNG) {
+  region.produce(region => shuffleCore(region, rng));
+}
+
+function shuffleCore(region: Region, rng: RNG){
   if (region.children.length <= 1) return;
 
-  // Fisher-Yates 洗牌算法
   const children = [...region.children];
   for (let i = children.length - 1; i > 0; i--) {
     const j = rng.nextInt(i + 1);
-    // 交换两个 part 的整个 position 数组
-    const temp = children[i].value.position;
-    children[i].value.position = children[j].value.position;
-    children[j].value.position = temp;
+    const posI = [...children[i].value.position];
+    const posJ = [...children[j].value.position];
+    children[i].produce(draft => {
+      draft.position = posJ;
+    });
+    children[j].produce(draft => {
+      draft.position = posI;
+    });
   }
-}
+}
\ No newline at end of file
diff --git a/src/samples/tic-tac-toe.ts b/src/samples/tic-tac-toe.ts
index 05423e5..54f13e8 100644
--- a/src/samples/tic-tac-toe.ts
+++ b/src/samples/tic-tac-toe.ts
@@ -1,35 +1,30 @@
-import { IGameContext, createGameCommand } from '../core/game';
-import { createCommandRegistry, registerCommand } from '../utils/command';
+import {createGameCommand, createGameCommandRegistry, IGameContext} from '../core/game';
+import { registerCommand } from '../utils/command';
 import type { Part } from '../core/part';
 
-export type TicTacToeState = {
-    currentPlayer: 'X' | 'O';
-    winner: 'X' | 'O' | 'draw' | null;
-    moveCount: number;
-};
-
-export type TicTacToeContext = IGameContext<TicTacToeState>;
-
 type TurnResult = {
     winner: 'X' | 'O' | 'draw' | null;
 };
 
-export function createInitialState(): TicTacToeState {
+export function createInitialState() {
     return {
-        currentPlayer: 'X',
-        winner: null,
+        currentPlayer: 'X' as 'X' | 'O',
+        winner: null as 'X' | 'O' | 'draw' | null,
         moveCount: 0,
     };
 }
+export type TicTacToeState = ReturnType<typeof createInitialState>;
 
-export function getBoardRegion(host: TicTacToeContext) {
+export function getBoardRegion(host: IGameContext<TicTacToeState>) {
     return host.regions.get('board');
 }
 
-export function isCellOccupied(host: TicTacToeContext, row: number, col: number): boolean {
+export function isCellOccupied(host: IGameContext<TicTacToeState>, row: number, col: number): boolean {
     const board = getBoardRegion(host);
     return board.value.children.some(
-        (child: { value: { position: number[] } }) => child.value.position[0] === row && child.value.position[1] === col
+        part => {
+            return part.value.position[0] === row && part.value.position[1] === col;
+        }
     );
 }
 
@@ -52,7 +47,7 @@ export function hasWinningLine(positions: number[][]): boolean {
     );
 }
 
-export function checkWinner(host: TicTacToeContext): 'X' | 'O' | 'draw' | null {
+export function checkWinner(host: IGameContext<TicTacToeState>): 'X' | 'O' | 'draw' | null {
     const parts = Object.values(host.parts.collection.value).map((s: { value: Part }) => s.value);
 
     const xPositions = parts.filter((_: Part, i: number) => i % 2 === 0).map((p: Part) => p.position);
@@ -64,7 +59,7 @@ export function checkWinner(host: TicTacToeContext): 'X' | 'O' | 'draw' | null {
     return null;
 }
 
-export function placePiece(host: TicTacToeContext, row: number, col: number, moveCount: number) {
+export function placePiece(host: IGameContext<TicTacToeState>, row: number, col: number, moveCount: number) {
     const board = getBoardRegion(host);
     const piece: Part = {
         id: `piece-${moveCount}`,
@@ -74,7 +69,9 @@ export function placePiece(host: TicTacToeContext, row: number, col: number, mov
         position: [row, col],
     };
     host.parts.add(piece);
-    board.value.children.push(host.parts.get(piece.id));
+    board.produce(draft => {
+        draft.children.push(host.parts.get(piece.id));
+    });
 }
 
 const setup = createGameCommand<TicTacToeState, { winner: 'X' | 'O' | 'draw' | null }>(
@@ -128,6 +125,6 @@ const turn = createGameCommand<TicTacToeState, TurnResult>(
     }
 );
 
-export const registry = createCommandRegistry<TicTacToeContext>();
+export const registry = createGameCommandRegistry<TicTacToeState>();
 registerCommand(registry, setup);
 registerCommand(registry, turn);
\ No newline at end of file
diff --git a/src/utils/entity.ts b/src/utils/entity.ts
index 7cff6bd..b50993e 100644
--- a/src/utils/entity.ts
+++ b/src/utils/entity.ts
@@ -1,80 +1,43 @@
-import {Signal, signal} from "@preact/signals-core";
+import {Signal, signal, SignalOptions} from "@preact/signals-core";
+import {create} from 'mutative';
 
-export type Entity = {
-  id: string;
-};
-
-export type EntityAccessor<T extends Entity> = {
-  id: string;
-  value: T;
+export class Entity<T> extends Signal<T> {
+  public constructor(public readonly id: string, t?: T, options?: SignalOptions<T>) {
+    super(t, options);
+  }
+  produce(fn: (draft: T) => void) {
+    this.value = create(this.value, fn);
+  }
 }
 
-function createReactiveProxy<T extends Entity>(entitySignal: Signal<T>): T {
-  return new Proxy({} as T, {
-    get(_target, prop) {
-      const current = entitySignal.value;
-      const value = current[prop as keyof T];
-      if (typeof value === 'function') {
-        return value.bind(current);
-      }
-      return value;
-    },
-    set(_target, prop, value) {
-      const current = entitySignal.value;
-      entitySignal.value = { ...current, [prop]: value };
-      return true;
-    },
-    ownKeys(_target) {
-      return Reflect.ownKeys(entitySignal.value);
-    },
-    getOwnPropertyDescriptor(_target, prop) {
-      return Reflect.getOwnPropertyDescriptor(entitySignal.value, prop);
-    },
-  });
+export function entity<T = undefined>(id: string, t?: T, options?: SignalOptions<T>) {
+  return new Entity<T>(id, t, options);
 }
 
-function createReactiveAccessor<T extends Entity>(id: string, entitySignal: Signal<T>): EntityAccessor<T> {
-  const proxy = createReactiveProxy(entitySignal);
-  return {
-    id,
-    get value() {
-      return proxy;
-    },
-    set value(value: T) {
-      entitySignal.value = value;
-    }
-  } as EntityAccessor<T>;
+export type EntityCollection<T> = {
+  collection: Signal<Record<string, Entity<T>>>;
+  remove(...ids: string[]): void;
+  add(...entities: (T & {id: string})[]): void;
+  get(id: string): Entity<T>;
 }
 
-export function createEntityCollection<T extends Entity>() {
-  const collection = signal({} as Record<string, Signal<T>>);
+export function createEntityCollection<T>(): EntityCollection<T> {
+  const collection = signal({} as Record<string, Entity<T>>);
   const remove = (...ids: string[]) => {
     collection.value = Object.fromEntries(
-      Object.entries(collection.value).filter(([id]) => !ids.includes(id)),
+        Object.entries(collection.value).filter(([id]) => !ids.includes(id)),
     );
   };
-  
-  const add = (...entities: T[]) => {
+
+  const add = (...entities: (T & {id: string})[]) => {
     collection.value = {
       ...collection.value,
-      ...Object.fromEntries(entities.map((entity) => [entity.id, signal(entity)])),
+      ...Object.fromEntries(entities.map((e) => [e.id, entity(e.id, e)])),
     };
   };
-  
-  const get = (id: string): EntityAccessor<T> => {
-    const entitySignal = collection.value[id];
-    if (!entitySignal) {
-      return {
-        id,
-        get value() {
-          return undefined as unknown as T;
-        },
-        set value(_value: T) {}
-      } as EntityAccessor<T>;
-    }
-    return createReactiveAccessor(id, entitySignal);
-  }
-  
+
+  const get = (id: string) => collection.value[id];
+
   return {
     collection,
     remove,