docs(ai-transport): migrate UIMessageCodec to createUIMessageCodec factory

src/pages/docs/ai-transport/api/index.mdx

@@ -37,7 +37,7 @@ See the individual reference pages for the full API.
 | --- | --- | --- |
 | Core | `@ably/ai-transport` | `createClientSession`, `createAgentSession`, `Invocation`, `Codec` interface |
 | React | `@ably/ai-transport/react` | `ClientSessionProvider`, `useClientSession`, `useView`, `useTree`, `useCreateView`, `useMessagesWithSeed`, `useAblyMessages`, `createSessionHooks` |
-| Vercel | `@ably/ai-transport/vercel` | `UIMessageCodec`, Vercel-bound `createClientSession` and `createAgentSession`, `createChatTransport`, `vercelRunOutcome` |
+| Vercel | `@ably/ai-transport/vercel` | `createUIMessageCodec`, Vercel-bound `createClientSession` and `createAgentSession`, `createChatTransport`, `vercelRunOutcome` |
 | Vercel React | `@ably/ai-transport/vercel/react` | `ChatTransportProvider`, `useChatTransport`, `useMessageSync`, `useMessagesWithSeed`, plus the Vercel-baked re-exports of `ClientSessionProvider`, `useClientSession`, `useView`, `useCreateView`, `useTree`, and `useAblyMessages` |
 
 <Aside data-type='note'>
@@ -82,8 +82,8 @@ The Vercel entry points re-export the core factories with the codec pre-bound. I
     link: '/docs/ai-transport/api/javascript/vercel/chat-transport',
   },
   {
-    title: 'UIMessageCodec',
-    description: 'The pre-built codec for the Vercel AI SDK and its type parameters.',
+    title: 'createUIMessageCodec',
+    description: 'The factory for the pre-built Vercel AI SDK codec, and its type parameters.',
     image: 'icon-tech-vercel',
     link: '/docs/ai-transport/api/javascript/vercel/codec',
   },

src/pages/docs/ai-transport/api/javascript/core/agent-session.mdx

@@ -15,7 +15,7 @@ Construct one with `createAgentSession` from the core entry point. For Vercel `U
 ```javascript
 import * as Ably from 'ably';
 import { createAgentSession, Invocation } from '@ably/ai-transport';
-import { UIMessageCodec } from '@ably/ai-transport/vercel';
+import { createUIMessageCodec } from '@ably/ai-transport/vercel';
 
 const ably = new Ably.Realtime({ key: process.env.ABLY_API_KEY });
 
@@ -24,7 +24,7 @@ const invocation = Invocation.fromJSON(await req.json());
 const session = createAgentSession({
   client: ably,
   channelName: invocation.sessionName,
-  codec: UIMessageCodec,
+  codec: createUIMessageCodec(),
 });
 
 await session.connect();
@@ -54,14 +54,14 @@ Construct an `AgentSession` bound to an Ably channel. The session does not attac
 ```javascript
 import * as Ably from 'ably';
 import { createAgentSession } from '@ably/ai-transport';
-import { UIMessageCodec } from '@ably/ai-transport/vercel';
+import { createUIMessageCodec } from '@ably/ai-transport/vercel';
 
 const ably = new Ably.Realtime({ key: process.env.ABLY_API_KEY });
 
 const session = createAgentSession({
   client: ably,
   channelName: 'conversation-42',
-  codec: UIMessageCodec,
+  codec: createUIMessageCodec(),
 });
 ```
 </Code>
@@ -609,7 +609,7 @@ An HTTP handler that sets up the session, creates a Run, rebuilds the conversati
 ```javascript
 import * as Ably from 'ably';
 import { createAgentSession, Invocation } from '@ably/ai-transport';
-import { UIMessageCodec } from '@ably/ai-transport/vercel';
+import { createUIMessageCodec } from '@ably/ai-transport/vercel';
 
 const ably = new Ably.Realtime({ key: process.env.ABLY_API_KEY });
 
@@ -619,7 +619,7 @@ export async function POST(req: Request) {
   const session = createAgentSession({
     client: ably,
     channelName: invocation.sessionName,
-    codec: UIMessageCodec,
+    codec: createUIMessageCodec(),
   });
 
   await session.connect();

src/pages/docs/ai-transport/api/javascript/core/client-session.mdx

@@ -15,14 +15,14 @@ Construct one with `createClientSession` from the core entry point. For Vercel `
 ```javascript
 import * as Ably from 'ably';
 import { createClientSession } from '@ably/ai-transport';
-import { UIMessageCodec } from '@ably/ai-transport/vercel';
+import { createUIMessageCodec } from '@ably/ai-transport/vercel';
 
 const ably = new Ably.Realtime({ authUrl: '/api/auth/token' });
 
 const session = createClientSession({
   client: ably,
   channelName: 'conversation-42',
-  codec: UIMessageCodec,
+  codec: createUIMessageCodec(),
 });
 
 await session.connect();
@@ -83,14 +83,14 @@ Construct a `ClientSession` bound to an Ably channel. The session does not attac
 ```javascript
 import * as Ably from 'ably';
 import { createClientSession } from '@ably/ai-transport';
-import { UIMessageCodec } from '@ably/ai-transport/vercel';
+import { createUIMessageCodec } from '@ably/ai-transport/vercel';
 
 const ably = new Ably.Realtime({ authUrl: '/api/auth/token' });
 
 const session = createClientSession({
   client: ably,
   channelName: 'conversation-42',
-  codec: UIMessageCodec,
+  codec: createUIMessageCodec(),
 });
 ```
 </Code>
@@ -224,7 +224,7 @@ Publish a codec input event that targets this Run. The steering message carries
 
 <Code>
 ```javascript
-const { published, outcome } = activeRun.steer(UIMessageCodec.createUserMessage({
+const { published, outcome } = activeRun.steer(createUIMessageCodec().createUserMessage({
   id: crypto.randomUUID(),
   role: 'user',
   parts: [{ type: 'text', text: 'Also include vegan options.' }],
@@ -342,14 +342,14 @@ End-to-end usage covering construction, connect, send, and teardown.
 ```javascript
 import * as Ably from 'ably';
 import { createClientSession } from '@ably/ai-transport';
-import { UIMessageCodec } from '@ably/ai-transport/vercel';
+import { createUIMessageCodec } from '@ably/ai-transport/vercel';
 
 const ably = new Ably.Realtime({ authUrl: '/api/auth/token' });
 
 const session = createClientSession({
   client: ably,
   channelName: 'conversation-42',
-  codec: UIMessageCodec,
+  codec: createUIMessageCodec(),
 });
 
 await session.connect();
@@ -358,7 +358,7 @@ session.view.on('update', () => {
   render(session.view.getMessages().map(({ message }) => message));
 });
 
-const clientRun = await session.view.send(UIMessageCodec.createUserMessage({
+const clientRun = await session.view.send(createUIMessageCodec().createUserMessage({
   id: crypto.randomUUID(),
   role: 'user',
   parts: [{ type: 'text', text: 'Plan a 3-day trip to Lisbon.' }],

src/pages/docs/ai-transport/api/javascript/core/codec.mdx

@@ -9,7 +9,7 @@ redirect_from:
 
 The `Codec` interface is the bridge between an AI framework and Ably channel messages. It describes the wire as a flat stream of input and output events and folds those events into a per-Run projection that the SDK extracts messages from for the conversation tree.
 
-Implement `Codec<TInput, TOutput, TProjection, TMessage>` to integrate any AI framework with AI Transport. The SDK ships [`UIMessageCodec`](/docs/ai-transport/api/javascript/vercel/codec) for the Vercel AI SDK. For other frameworks, implement the methods below.
+Implement `Codec<TInput, TOutput, TProjection, TMessage>` to integrate any AI framework with AI Transport. The SDK ships the Vercel codec via [`createUIMessageCodec()`](/docs/ai-transport/api/javascript/vercel/codec) for the Vercel AI SDK. For other frameworks, implement the methods below.
 
 <Code>
 ```typescript

src/pages/docs/ai-transport/api/javascript/vercel/chat-transport.mdx

@@ -1,13 +1,13 @@
 ---
 title: "ChatTransport"
 meta_description: "API reference for the AI Transport Vercel ChatTransport adapter and the Vercel-bound createClientSession and createAgentSession factories."
-meta_keywords: "Vercel AI SDK, AI Transport, ChatTransport, createChatTransport, createClientSession, createAgentSession, UIMessageCodec, Ably"
+meta_keywords: "Vercel AI SDK, AI Transport, ChatTransport, createChatTransport, createClientSession, createAgentSession, createUIMessageCodec, Ably"
 redirect_from:
   - /docs/ai-transport/api-reference/vercel
   - /docs/ai-transport/api/javascript/vercel
 ---
 
-The Vercel entry point pre-binds the [`UIMessageCodec`](/docs/ai-transport/api/javascript/vercel/codec) and exposes a `ChatTransport` adapter that satisfies the contract Vercel AI SDK's `useChat` hook expects. Use these factories whenever you build a chat UI on top of `useChat` so you do not have to wire the codec yourself.
+The Vercel entry point pre-binds the [Vercel codec](/docs/ai-transport/api/javascript/vercel/codec) and exposes a `ChatTransport` adapter that satisfies the contract Vercel AI SDK's `useChat` hook expects. Use these factories whenever you build a chat UI on top of `useChat` so you do not have to wire the codec yourself.
 
 <Code>
 ```javascript
@@ -33,7 +33,7 @@ React-side wiring (`ChatTransportProvider`, `useChatTransport`, `useMessageSync`
 
 <MethodSignature>{`function createClientSession(options: VercelClientSessionOptions): ClientSession<VercelInput, VercelOutput, VercelProjection, UIMessage>`}</MethodSignature>
 
-A pre-bound version of the core [`createClientSession`](/docs/ai-transport/api/javascript/core/client-session#constructor) with `codec: UIMessageCodec` already supplied. The `api` default is set on [`createChatTransport`](#create-chat-transport), not here.
+A pre-bound version of the core [`createClientSession`](/docs/ai-transport/api/javascript/core/client-session#constructor) with the Vercel codec already supplied. The `api` default is set on [`createChatTransport`](#create-chat-transport), not here.
 
 <Code>
 ```javascript
@@ -65,13 +65,13 @@ const session = createClientSession({
 
 ### Returns <a id="create-client-session-returns"/>
 
-`ClientSession<VercelInput, VercelOutput, VercelProjection, UIMessage>`. A client session whose codec is pre-bound to `UIMessageCodec`.
+`ClientSession<VercelInput, VercelOutput, VercelProjection, UIMessage>`. A client session whose codec is pre-bound to the Vercel codec.
 
 ## Create a Vercel agent session <a id="create-agent-session"/>
 
 <MethodSignature>{`function createAgentSession(options: VercelAgentSessionOptions): AgentSession<VercelOutput, VercelProjection, UIMessage>`}</MethodSignature>
 
-A pre-bound version of the core [`createAgentSession`](/docs/ai-transport/api/javascript/core/agent-session#constructor) with `codec: UIMessageCodec` already supplied. Construct one inside your HTTP handler when the request arrives.
+A pre-bound version of the core [`createAgentSession`](/docs/ai-transport/api/javascript/core/agent-session#constructor) with the Vercel codec already supplied. Construct one inside your HTTP handler when the request arrives.
 
 <Code>
 ```javascript
@@ -108,7 +108,7 @@ Subscribe to non-fatal session-level errors with [`session.on('error')`](/docs/a
 
 ### Returns <a id="create-agent-session-returns"/>
 
-`AgentSession<VercelOutput, VercelProjection, UIMessage>`. An agent session whose codec is pre-bound to `UIMessageCodec`.
+`AgentSession<VercelOutput, VercelProjection, UIMessage>`. An agent session whose codec is pre-bound to the Vercel codec.
 
 ## Create a chat transport <a id="create-chat-transport"/>
 

src/pages/docs/ai-transport/api/javascript/vercel/codec.mdx

@@ -1,25 +1,26 @@
 ---
-title: "UIMessageCodec"
-meta_description: "API reference for UIMessageCodec, the pre-built AI Transport codec for the Vercel AI SDK."
-meta_keywords: "Vercel AI SDK, AI Transport, UIMessageCodec, VercelInput, VercelOutput, VercelProjection, codec, Ably"
+title: "createUIMessageCodec"
+meta_description: "API reference for createUIMessageCodec, the factory for the pre-built AI Transport codec for the Vercel AI SDK."
+meta_keywords: "Vercel AI SDK, AI Transport, createUIMessageCodec, UIMessageCodec, VercelInput, VercelOutput, VercelProjection, codec, Ably"
 ---
 
-`UIMessageCodec` is the pre-built codec for the Vercel AI SDK. It implements [`Codec<VercelInput, VercelOutput, VercelProjection, UIMessage>`](/docs/ai-transport/api/javascript/core/codec) so a session can encode `UIMessageChunk` events out and decode them back into `UIMessage` objects without a custom implementation.
+`createUIMessageCodec()` returns the pre-built codec for the Vercel AI SDK. The returned codec implements [`Codec<VercelInput, VercelOutput, VercelProjection, UIMessage>`](/docs/ai-transport/api/javascript/core/codec) so a session can encode `UIMessageChunk` events out and decode them back into `UIMessage` objects without a custom implementation.
 
-You rarely import `UIMessageCodec` directly. The Vercel-pre-bound [`createClientSession`](/docs/ai-transport/api/javascript/vercel/chat-transport#create-client-session) and [`createAgentSession`](/docs/ai-transport/api/javascript/vercel/chat-transport#create-agent-session) already supply it. Import it explicitly when you build a codec wrapper, run the encoder or decoder outside of a session, or compose `UIMessageCodec` into a different codec.
+You rarely call `createUIMessageCodec()` yourself. The Vercel-pre-bound [`createClientSession`](/docs/ai-transport/api/javascript/vercel/chat-transport#create-client-session) and [`createAgentSession`](/docs/ai-transport/api/javascript/vercel/chat-transport#create-agent-session) already supply the codec. Call it explicitly when you build a codec wrapper, run the encoder or decoder outside of a session, or compose the codec into a different codec.
 
 <Code>
 ```javascript
-import { UIMessageCodec } from '@ably/ai-transport/vercel';
+import { createUIMessageCodec } from '@ably/ai-transport/vercel';
 
-const decoder = UIMessageCodec.createDecoder();
-const projection = UIMessageCodec.init();
+const codec = createUIMessageCodec();
+const decoder = codec.createDecoder();
+const projection = codec.init();
 ```
 </Code>
 
 ## Properties <a id="properties"/>
 
-`UIMessageCodec` is a value, not a type. It satisfies the full [`Codec`](/docs/ai-transport/api/javascript/core/codec) interface for the Vercel `TInput`, `TOutput`, `TProjection`, and `TMessage` parameters listed below.
+`createUIMessageCodec()` is a factory, not a type. Each call returns a fresh, stateless codec value that satisfies the full [`Codec`](/docs/ai-transport/api/javascript/core/codec) interface for the Vercel `TInput`, `TOutput`, `TProjection`, and `TMessage` parameters listed below. Because the codec is stateless, hold a single instance at module scope (or, in React, `useMemo(() => createUIMessageCodec(), [])`) and reuse it rather than calling the factory inline on every render.
 
 <Table id='UIMessageCodecProperties'>
 
@@ -40,6 +41,10 @@ const projection = UIMessageCodec.init();
 
 ## Type parameters <a id="types"/>
 
+`createUIMessageCodec` is generic over the AI SDK's three `UIMessage` type parameters — `createUIMessageCodec<TMetadata, TDataParts, TTools>()`. Supplying concrete types specialises the codec so `getMessages` (and a session's `view.getMessages()`) return messages whose `metadata`, data parts, and tool parts carry your types instead of the SDK defaults; omitting them preserves the default inference. The same parameters thread through [`createClientSession`](/docs/ai-transport/api/javascript/vercel/chat-transport#create-client-session), [`createAgentSession`](/docs/ai-transport/api/javascript/vercel/chat-transport#create-agent-session), and [`createChatTransport`](/docs/ai-transport/api/javascript/vercel/chat-transport#create-chat-transport). See [Typed messages](/docs/ai-transport/frameworks/vercel-ai-sdk-ui#typed-messages) for the end-to-end pattern.
+
+`VercelInput`, `VercelOutput`, and `VercelProjection` are likewise generic over the same three parameters, each defaulting to the SDK default. The tables below show the default instantiation.
+
 <Table id='VercelInput'>
 
 | Property | Description | Type |
@@ -72,21 +77,22 @@ Decode a single Ably message and fold the resulting events into a fresh projecti
 
 <Code>
 ```javascript
-import { UIMessageCodec } from '@ably/ai-transport/vercel';
+import { createUIMessageCodec } from '@ably/ai-transport/vercel';
 
-const decoder = UIMessageCodec.createDecoder();
-let projection = UIMessageCodec.init();
+const codec = createUIMessageCodec();
+const decoder = codec.createDecoder();
+let projection = codec.init();
 
 channel.subscribe((message) => {
   if (!message.serial) return; // live channel-subscribe messages always carry one
   const { inputs, outputs } = decoder.decode(message);
   for (const input of inputs) {
-    projection = UIMessageCodec.fold(projection, input, { serial: message.serial });
+    projection = codec.fold(projection, input, { serial: message.serial });
   }
   for (const output of outputs) {
-    projection = UIMessageCodec.fold(projection, output, { serial: message.serial });
+    projection = codec.fold(projection, output, { serial: message.serial });
   }
-  render(UIMessageCodec.getMessages(projection).map((entry) => entry.message));
+  render(codec.getMessages(projection).map((entry) => entry.message));
 });
 ```
 </Code>

src/pages/docs/ai-transport/api/react/core/providers.mdx

@@ -16,14 +16,14 @@ Nest multiple providers with distinct `channelName` values to manage more than o
 import * as Ably from 'ably';
 import { AblyProvider } from 'ably/react';
 import { ClientSessionProvider } from '@ably/ai-transport/react';
-import { UIMessageCodec } from '@ably/ai-transport/vercel';
+import { createUIMessageCodec } from '@ably/ai-transport/vercel';
 
 const ably = new Ably.Realtime({ authUrl: '/api/auth/token' });
 
 function App() {
   return (
     <AblyProvider client={ably}>
-      <ClientSessionProvider channelName="conversation-42" codec={UIMessageCodec}>
+      <ClientSessionProvider channelName="conversation-42" codec={createUIMessageCodec()}>
         <Chat />
       </ClientSessionProvider>
     </AblyProvider>
@@ -126,15 +126,15 @@ Nested providers with distinct channel names and a child component that addresse
 import * as Ably from 'ably';
 import { AblyProvider } from 'ably/react';
 import { ClientSessionProvider, useClientSession } from '@ably/ai-transport/react';
-import { UIMessageCodec } from '@ably/ai-transport/vercel';
+import { createUIMessageCodec } from '@ably/ai-transport/vercel';
 
 const ably = new Ably.Realtime({ authUrl: '/api/auth/token' });
 
 function App() {
   return (
     <AblyProvider client={ably}>
-      <ClientSessionProvider channelName="ai:main" codec={UIMessageCodec}>
-        <ClientSessionProvider channelName="ai:aux" codec={UIMessageCodec}>
+      <ClientSessionProvider channelName="ai:main" codec={createUIMessageCodec()}>
+        <ClientSessionProvider channelName="ai:aux" codec={createUIMessageCodec()}>
           <Chat />
         </ClientSessionProvider>
       </ClientSessionProvider>