feat(agents): experimental ThinkHarness, Think's agent loop as a Lifecycle capability

.changeset/streams-legacy-table-shared.md

@@ -0,0 +1,5 @@
+---
+"agents": patch
+---
+
+`Streams` rechecks that the v1 chunk table still exists before using it. Two Streams instances on one object, such as a host's own and the one `ThinkHarness` keeps, each remembered the table separately, so after one folded the last v1 rows and dropped the table the other failed its next append with `no such table`.

.changeset/think-harness.md

@@ -0,0 +1,7 @@
+---
+"agents": patch
+---
+
+Add `ThinkHarness` from the new experimental `agents/harness/think` entry point. It runs Think's agent loop as a Lifecycle capability with the same shape as `PiHarness` (`prompt`, `submit`, `wait`, `abort`, `sessions`, `session(id)`), and implements the shared harness interface Channels serves.
+
+The harness owns its storage: transcripts in the Sessions tables, with `branches()`, `search()` and `compact()` on each session, and in-flight model output in the Streams tables, so a host installs only the harness. Each session has one Lifecycle wake job, so a turn interrupted by an eviction picks up from its last durable write: a cut-short model call is rebuilt from its stream and continued in the same message, and a cut-short tool call is reported to the model, or rerun when the tool carries `recovery: "rerun"`. `ThinkChat` serves a session over Think's `useAgentChat` WebSocket protocol. See [Think harness](https://github.com/cloudflare/agents/blob/main/docs/agents/harnesses/think.md).

docs/agents/index.md

@@ -81,6 +81,7 @@ The differentiator is not "we have durable state" — it is what happens when a
 - [Models (Experimental)](./models.md) - `createAI` — one AI SDK provider for Workers AI and third-party catalog models, same string space
 - [Models for pi-ai (Beta)](./models-pi-ai.md) - `createAI` for pi-ai: Workers AI ids and third-party models through AI Gateway, as a pi-ai provider
 - [Pi harness (Beta)](./harnesses/pi.md) - Host pi-durable sessions in a Durable Object with durable storage and lifecycle wakeups
+- [Think harness (Experimental)](./harnesses/think.md) - Run Think's agent loop as a Lifecycle capability, with transcripts in Sessions, output in Streams, and turns that survive eviction
 - TODO: [RAG (Retrieval Augmented Generation)](./rag.md) - Vector search with Vectorize
 - [Sessions (Experimental)](./sessions.md) - Durable message trees, streamed history, compaction, search, and lossless attachment offload
 - [Context (Experimental)](./context.md) - System-prompt blocks, frozen prompts, writable/searchable/loadable providers, and their tools

examples/next/README.md

@@ -19,6 +19,7 @@ lands.
 | [`dynamic-agents`](./dynamic-agents)                     | This PR   | A supervisor runs user-submitted code as facets: isolated storage, supervised abort, code upgrades over stable state                           |
 | [`harnesses/codex`](./harnesses/codex)                   | This PR   | A static Codex Rust/Wasm loop composed as a Lifecycle capability, using LanguageModelV4 and Shell Workspace                                    |
 | [`harnesses/pi`](./harnesses/pi)                         | This PR   | Experimental: pi-durable sessions on `agents/harness/pi`, with Workspace tools and a JavaScript `exec` from `@cloudflare/computer`             |
+| [`harnesses/think`](./harnesses/think)                   | This PR   | Experimental: Think's agent loop on a plain `DurableObject` with `agents/harness/think`, served to `useAgentChat` by `ThinkChat`               |
 | [`harnesses/self-modifying`](./harnesses/self-modifying) | This PR   | A Lifecycle capability runs editable harness revisions in fresh Dynamic Workers with trusted System tools and auto-discovered Custom tools     |
 | [`models`](./models)                                     | This PR   | One `createAI` per framework (AI SDK and pi-ai): `@cf/` ids for Workers AI, vendor models routed through AI Gateway                            |
 | [`channels`](./channels)                                 | This PR   | Agents on different harnesses served through `Channels.forHarness` and one `ChannelGateway`, to a browser client and terminal clients          |

examples/next/harnesses/think/README.md

@@ -0,0 +1,65 @@
+# Think harness
+
+An experimental example of `ThinkHarness` from `agents/harness/think`: Think's
+agent loop as a Lifecycle capability on a plain Durable Object, served to
+`useAgentChat` by `ThinkChat`.
+
+`src/server.ts` composes three capabilities:
+
+- `ThinkHarness` keeps the transcript and runs turns with the AI SDK. It
+  keeps each model call's output in storage while it streams, and one
+  Lifecycle job per session wakes the object after an eviction.
+- `WebSockets` accepts the browser's connection.
+- `ThinkChat` speaks Think's `cf_agent_chat_*` protocol over it, so the
+  client is the stock `useAgentChat` from `agents/chat/react`.
+
+```ts
+export class ThinkAgent extends DurableObject<Env> {
+  readonly harness = new ThinkHarness({
+    model: createAI({ binding: this.env.AI })("@cf/moonshotai/kimi-k2.7-code"),
+    tools: { getWeather, sendNotification, getUserTimezone }
+  });
+  readonly webSockets = new WebSockets();
+  readonly chat = new ThinkChat({
+    harness: this.harness,
+    webSockets: this.webSockets
+  });
+  readonly lifecycle = Lifecycle.install(this)
+    .use(this.harness)
+    .use(this.webSockets)
+    .use(this.chat);
+}
+```
+
+Each browser gets its own chat, named by a random id kept in
+`localStorage`, so visitors to a deployed copy do not share a transcript.
+
+The tools show the three ways a tool call runs:
+
+| Tool               | Runs                    | After an eviction cuts a call short                |
+| ------------------ | ----------------------- | -------------------------------------------------- |
+| `getWeather`       | on the server           | runs again, because it carries `recovery: "rerun"` |
+| `sendNotification` | on the server, approved | reported to the model as interrupted (the default) |
+| `getUserTimezone`  | in the browser          | waits for the browser's result, as it did before   |
+
+## Run locally
+
+```sh
+pnpm install
+pnpm run start
+```
+
+The example uses the remote Workers AI binding and may incur Workers AI
+usage. It needs no API key.
+
+## Try
+
+- "What is the weather in Lisbon?" runs a server tool.
+- "Notify Sam that lunch is ready" asks for your approval first.
+- "What time zone am I in?" runs a tool in the browser.
+- Refresh the page while an answer streams. The client reconnects and the
+  stream picks up where it was.
+
+## Learn more
+
+- [Think harness docs](../../../../docs/agents/harnesses/think.md)

examples/next/harnesses/think/env.d.ts

@@ -0,0 +1,14 @@
+/* eslint-disable */
+// Generated by Wrangler by running `wrangler types --include-runtime=false env.d.ts` (hash: 0cb7d4d3f8bfd65f4a85db3f24bf892b)
+interface __BaseEnv_Env {
+  AI: Ai;
+  ThinkAgent: DurableObjectNamespace<import("./src/server").ThinkAgent>;
+}
+declare namespace Cloudflare {
+  interface GlobalProps {
+    mainModule: typeof import("./src/server");
+    durableNamespaces: "ThinkAgent";
+  }
+  interface Env extends __BaseEnv_Env {}
+}
+interface Env extends __BaseEnv_Env {}

examples/next/harnesses/think/index.html

@@ -0,0 +1,21 @@
+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="UTF-8" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <link rel="icon" href="/favicon.ico" />
+    <title>Think harness</title>
+    <script>
+      (() => {
+        const stored = localStorage.getItem("theme");
+        const mode = stored || "light";
+        document.documentElement.setAttribute("data-mode", mode);
+        document.documentElement.style.colorScheme = mode;
+      })();
+    </script>
+  </head>
+  <body>
+    <div id="root"></div>
+    <script type="module" src="/src/client.tsx"></script>
+  </body>
+</html>

examples/next/harnesses/think/package.json

@@ -0,0 +1,37 @@
+{
+  "name": "@cloudflare/agents-next-think-harness-example",
+  "description": "Experimental: Think's agent loop on a plain Durable Object with agents/harness/think, served to useAgentChat",
+  "private": true,
+  "type": "module",
+  "version": "0.0.0",
+  "scripts": {
+    "start": "vite dev",
+    "build": "vite build",
+    "deploy": "vite build && wrangler deploy",
+    "typecheck": "tsc --noEmit",
+    "types": "wrangler types env.d.ts --include-runtime false"
+  },
+  "dependencies": {
+    "@cloudflare/kumo": "^2.6.0",
+    "@phosphor-icons/react": "^2.1.10",
+    "@streamdown/code": "^1.1.1",
+    "agents": "*",
+    "ai": "^7.0.0",
+    "react": "^19.2.7",
+    "react-dom": "^19.2.7",
+    "streamdown": "^2.5.0",
+    "zod": "^4.5.4"
+  },
+  "devDependencies": {
+    "@cloudflare/vite-plugin": "1.62.3",
+    "@cloudflare/workers-types": "^5.20260729.1",
+    "@tailwindcss/vite": "^4",
+    "@types/react": "^19.2.17",
+    "@types/react-dom": "^19.2.3",
+    "@vitejs/plugin-react": "^6.0.3",
+    "tailwindcss": "^4.3.2",
+    "typescript": "^6.0.3",
+    "vite": "^8.1.0",
+    "wrangler": "^4.145.0"
+  }
+}