DurableObjectChatPersistence

Source: src/Cloudflare/Workers/DurableObjectChatPersistence.ts

A BackingPersistence layer (Effect AI persistence module) backed by the surrounding Durable Object’s state.storage. Drop-in storage for Persistence.layerResultPersisted({ storeId }) so chat history, cached AI responses, or any other persisted state lives in the DO SQLite store with ${storeId}: key namespacing.

Multiple storeIds can coexist within a single Durable Object — keys are namespaced with a ${storeId}: prefix so they don’t collide.

Caution

TTL is currently ignored; Durable Object storage has no native TTL. If you need expiry, layer a TTL-aware backing store on top, or run a periodic clear.

Wiring it into a chat-backing DO

Persistence.layerResultPersisted({ storeId }) is the seam Effect AI exposes for cached/replayable AI calls. Layer DurableObjectChatPersistence underneath and every entry is stored in the DO’s state.storage under the alchemy.chat: prefix.

import * as Cloudflare from "alchemy/Cloudflare";
import * as Effect from "effect/Effect";
import * as Layer from "effect/Layer";
import { Chat, LanguageModel } from "effect/unstable/ai";
import { Persistence } from "effect/unstable/persistence";

export default class ChatBackend extends Cloudflare.DurableObjectNamespace<ChatBackend>()(
  "ChatBackend",
  Effect.gen(function* () {
    return Effect.gen(function* () {
      const persistence = yield* Persistence.layerResultPersisted({
        storeId: "alchemy.chat",
      }).pipe(Layer.provide(Cloudflare.DurableObjectChatPersistence));

      return {
        send: (threadId: string, prompt: string) =>
          LanguageModel.generateText({ prompt }).pipe(Effect.provide(persistence)),
      };
    });
  }),
) {}

Multiple stores in the same DO

Different storeIds namespace their keys with ${storeId}:, so one DO can keep, say, chat history and an audit log in separate stores without colliding.

const aiPersistence = yield* Persistence.layerResultPersisted({
  storeId: "alchemy.chat",
}).pipe(Layer.provide(Cloudflare.DurableObjectChatPersistence));

const auditPersistence = yield* Persistence.layerResultPersisted({
  storeId: "alchemy.audit",
}).pipe(Layer.provide(Cloudflare.DurableObjectChatPersistence));