[sam-goodwin]

Stacked on #16 (Alchemy beta.83).

The Room's replies now come from the Barista, a @yielded/agent agent on Workers AI. Its menu tool calls the Kitchen, an Effect container that serves tools over Alchemy's schemaless RPC.

Kitchen: tools served over container RPC

// kitchen/index.ts
export class Kitchen extends Cloudflare.Container<
  Kitchen,
  { menu: () => Effect.Effect<ReadonlyArray<MenuItem>> }
>()("Kitchen") {}

// kitchen/main.ts: the container's process, provided to the stacks
export default Kitchen.make(
  { main: import.meta.url, image: "oven/bun:latest" },
  Effect.succeed({ menu: () => Effect.succeed(MENU) }),
);

The tool calls the Kitchen; the schema lives at the model boundary

// room/menu.ts
export const Menu = Tool.make("menu", {
  description: "Today's café menu: every drink and pastry with its price in US dollars.",
  success: Schema.Array(Schema.Struct({ name: Schema.String, price: Schema.Number })),
});

export const menu = (kitchen: Kitchen) =>
  Effect.gen(function* () {
    const runtime = yield* Effect.context<RuntimeContext>();
    const start = kitchen.start({ enableInternet: false });
    return Effect.fn("Kitchen.menu")(
      function* () {
        yield* start;
        return yield* kitchen.menu();
      },
      Effect.orDie,
      Effect.provideContext(runtime),
    );
  });

The Barista

// room/barista.ts
const BaristaAgent = Agent.make("barista", {
  input: Schema.String,
  output: Output.text(Schema.String),
  instructions: "You are a friendly barista in a group chat at a café. … call the menu tool …",
  toolkit: Toolkit.make(Menu),
  policy: { maxTurns: 4, maxToolCalls: 2, maxDuration: "60 seconds" },
});

export class Barista extends Context.Service<
  Barista,
  { readonly reply: (conversation: string) => Stream.Stream<string, BaristaError> }
>()("Barista") {
  static readonly layer = (kitchen: Kitchen, model: Layer.Layer<LanguageModel | ProviderName | ModelName, never, RuntimeContext>) => …
}

Barista is a service so the library's internal types don't leak into the Room's declaration emit.

Room

+    const kitchen = yield* Kitchen;
     const ai = yield* Cloudflare.Workers.AI();
+    const model = Model.make("workers-ai", MODEL, ai.model({ model: MODEL, parameters: { maxTokens: 512 } }));
 …
-        Layer.provide(languageModel),
+        Layer.provide(Barista.layer(kitchen, model)),

 // room/reply.ts
-    yield* model.streamText({ prompt }).pipe(
-      Stream.filter((part) => part.type === "text-delta"),
-      Stream.map((part) => part.delta),
+    yield* barista.reply(transcript(conversation)).pipe(

Alchemy patch (to upstream)

patches/alchemy@2.0.0-beta.83.patch fixes the Workers AI LanguageModel for agents:

 const tryParseJsonArgs = (raw: unknown): unknown => {
+  // Workers AI sends `""` as the arguments of a call to a parameterless tool.
+  if (raw === "" || raw == null) return {};

     outputTokens: {
       total: completionTokens,
-      text: 0,
-      reasoning: 0,
+      text: Math.max(0, completionTokens - reasoningTokens),
+      reasoning: reasoningTokens,
     },

Dependencies

-  effect: 4.0.0
+  effect: 4.0.5          # @yielded/agent needs ^4.0.3 (and @effect/* 4.0.5 together)
+  "@yielded/agent": 0.1.0-beta.183
+peerDependencyRules:
+  allowedVersions:
+    effect: "4"          # Foldkit pins its effect peer to 4.0.0

alchemy dev now needs Docker for the Kitchen.

Tests

// backend/test/api.test.ts and frontend/test/chat.test.ts
"How much is a flat white?" → the assistant's reply contains "4.50" (only the Kitchen's menu knows it)

ALCHEMY_DEV=1 pnpm --filter @cafe/backend test      # 7/7
pnpm --filter @cafe/backend test                    # 7/7 (live, 3 runs)
ALCHEMY_DEV=1 pnpm test:e2e / pnpm test:e2e         # 6/6, 6/6

🤖 Generated with Claude Code

[github-actions]

Preview deployed

App: https://cafe-web-pr-17-e4ohbuapg62bvdhh.testing-2b2.workers.dev

Built from commit 0780050.

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