feat: add BaseGameClient for external integration

Introduces `BaseGameClient` to allow external environments (like C#)
to interact with the game engine. It provides mechanisms for:
- Reactive state selection via `select`
- Async event interception via `use`
- Lifecycle management and status tracking
- Interruption handling for async game loops

Updated `middleware.ts` to allow unregistering middleware via the
returned function from `use`.

src/core/game-client.ts

@@ -0,0 +1,103 @@
+import { createPromptContext, PromptCall } from "@/utils/command";
+import { createMiddlewareChain } from "@/utils/middleware";
+import { computed } from "@preact/signals-core";
+import { createGameContext, IGameContext } from "./game";
+
+export interface GameClient<E extends {} = {}, T extends {} = {}> {
+  // c# calls this to generate a ReactiveProperty<T>
+  select<K extends keyof E>(
+    type: K,
+    id: string,
+    callback: (t: E[K]) => void,
+  ): () => void;
+
+  // c# calls this to interrupt and capture async events
+  use<K extends keyof T>(
+    trigger: K,
+    callback: (ctx: T[K], next: () => Promise<any>) => Promise<any>,
+  ): () => void;
+}
+
+export type EntityMap = {};
+
+export type ClientTriggerMap = {
+  status: { status: ClientStatus; result?: unknown };
+  prompt: PromptCall;
+};
+
+export enum ClientStatus {
+  Idle = "idle",
+  Running = "running",
+  Disposed = "disposed",
+}
+export abstract class BaseGameClient<
+  T extends Record<string, unknown> = Record<string, unknown>,
+  R = unknown,
+> {
+  protected _initialState: T;
+  protected _context: IGameContext<T>;
+  protected _prompts = createPromptContext();
+  protected _status = ClientStatus.Idle;
+
+  protected _setStatus = createMiddlewareChain(
+    async (ctx: ClientTriggerMap["status"]) => {
+      this._status = ctx.status;
+      if (this._status === ClientStatus.Disposed) {
+        this._prompts.reset();
+      } else if (this._status === ClientStatus.Running) {
+        this._prompts.reset();
+        this._context._state.value = this._initialState;
+        const r = await this.start(this._context);
+        this._setStatus.execute({ status: ClientStatus.Idle, result: r });
+      }
+    },
+  );
+  constructor(is: T) {
+    this._initialState = is;
+    this._context = createGameContext(this._prompts, is);
+  }
+
+  setStatus(status: ClientStatus) {
+    this._setStatus.execute({ status });
+  }
+
+  abstract start(ctx: IGameContext<T>): Promise<R>;
+
+  protected assignSelector<S>(selector: (t: T) => S, callback: (s: S) => void) {
+    const selected = computed(() => selector(this._context.value));
+    return selected.subscribe(callback);
+  }
+
+  addInterruption() {
+    let resolve!: () => void;
+    const promise = new Promise<void>((resolver) => {
+      resolve = resolver;
+    });
+    this._context._state.addInterruption(promise);
+    return resolve;
+  }
+
+  useClient<K extends keyof ClientTriggerMap>(
+    trigger: K,
+    callback: (
+      ctx: ClientTriggerMap[K],
+      next: () => Promise<void>,
+    ) => Promise<void>,
+  ) {
+    if (trigger === "prompt") {
+      return this._prompts.handleCall.use(
+        callback as (
+          ctx: ClientTriggerMap["prompt"],
+          next: () => Promise<unknown>,
+        ) => Promise<void>,
+      );
+    } else if (trigger === "status") {
+      return this._setStatus.use(
+        callback as (
+          ctx: ClientTriggerMap["status"],
+          next: () => Promise<void>,
+        ) => Promise<void>,
+      );
+    }
+  }
+}

src/index.ts

@@ -24,6 +24,8 @@ export {
   moveToRegion,
 } from "./core/region";
 
+export * from "./core/game-client";
+
 // Utils
 export type {
   Command,

src/samples/tic-tac-toe.ts

@@ -1,6 +1,8 @@
 import { Part } from "@/core/part";
 import { createRegion } from "@/core/region";
 import { createPromptDef, IGameContext } from "@/core/game";
+import { BaseGameClient, GameClient } from "@/core/game-client";
+import { createMiddlewareChain } from "@/utils/middleware";
 
 const BOARD_SIZE = 3;
 const MAX_TURNS = BOARD_SIZE * BOARD_SIZE;
@@ -183,3 +185,62 @@ export async function placePiece(
     board.partMap[`${row},${col}`] = piece.id;
   });
 }
+
+type EntityMap = { parts: TicTacToePart };
+type TriggerMap = {
+  turn: { player: PlayerType; turn: number };
+};
+export class Client
+  extends BaseGameClient<TicTacToeState>
+  implements GameClient<EntityMap, TriggerMap>
+{
+  private onTurn = createMiddlewareChain(
+    async (ctx: { player: PlayerType; turn: number }) => {
+      return await turn(this._context, ctx.player, ctx.turn);
+    },
+  );
+
+  constructor() {
+    super(createInitialState());
+  }
+
+  async start(game: IGameContext<TicTacToeState>): Promise<TicTacToeState> {
+    while (true) {
+      const currentPlayer = game.value.currentPlayer;
+      const turnNumber = game.value.turn + 1;
+      const turnOutput = await this.onTurn.execute({
+        player: currentPlayer,
+        turn: turnNumber,
+      });
+
+      await game.produceAsync((state) => {
+        state.winner = turnOutput.winner;
+        if (!state.winner) {
+          state.currentPlayer = state.currentPlayer === "X" ? "O" : "X";
+          state.turn = turnNumber;
+        }
+      });
+      if (game.value.winner) break;
+    }
+
+    return game.value;
+  }
+  select<K extends keyof EntityMap>(
+    type: K,
+    id: string,
+    callback: (t: EntityMap[K]) => void,
+  ): () => void {
+    if (type === "parts")
+      return this.assignSelector((state) => state.parts[id], callback);
+    return function () {};
+  }
+  use<K extends keyof TriggerMap>(
+    trigger: K,
+    callback: (ctx: TriggerMap[K], next: () => Promise<any>) => Promise<any>,
+  ): () => void {
+    if (trigger === "turn") {
+      return this.onTurn.use(callback);
+    }
+    return function () {};
+  }
+}

src/utils/middleware.ts

@@ -1,28 +1,38 @@
 type Middleware<TContext, TReturn> = (
   context: TContext,
-  next: () => Promise<TReturn>
+  next: () => Promise<TReturn>,
 ) => Promise<TReturn>;
 
 export type MiddlewareChain<TContext, TReturn> = {
-  use: (middleware: Middleware<TContext, TReturn>) => void;
+  use: (middleware: Middleware<TContext, TReturn>) => () => void;
   execute: (context: TContext) => Promise<TReturn>;
 };
 
-export function createMiddlewareChain<TContext extends object, TReturn=TContext>(
-  fallback?: (context: TContext) => Promise<TReturn>
+export function createMiddlewareChain<
+  TContext extends object,
+  TReturn = TContext,
+>(
+  fallback?: (context: TContext) => Promise<TReturn>,
 ): MiddlewareChain<TContext, TReturn> {
   const middlewares: Middleware<TContext, TReturn>[] = [];
 
   return {
     use(middleware: Middleware<TContext, TReturn>) {
       middlewares.push(middleware);
+
+      return function () {
+        const index = middlewares.indexOf(middleware);
+        if (index !== -1) {
+          middlewares.splice(index, 1);
+        }
+      };
     },
     async execute(context: TContext) {
       let index = 0;
 
       async function dispatch(ctx: TContext): Promise<TReturn> {
         if (index >= middlewares.length) {
-          return fallback ? fallback(ctx) : ctx as unknown as TReturn;
+          return fallback ? fallback(ctx) : (ctx as unknown as TReturn);
         }
         const current = middlewares[index++];
         return current(ctx, () => dispatch(ctx));