feat (ui): extended regenerate support (#6773)

## Background

Reload was slightly misleading as a name. Regenerating any assistant
message should be supported.

## Summary

* rename `reload` to `regenerate` on chat
* support optional `messageId` param and regenerate on user msgs
* rename transport `submitMessages` and related to `sendMessages`

## Verification

Tested with `next` example.

Author: lgrammel

.changeset/seven-fans-speak.md

@@ -0,0 +1,5 @@
+---
+'ai': major
+---
+
+feat (ui): extended regenerate support

examples/next-openai/app/mcp/page.tsx

@@ -5,7 +5,7 @@ import { useChat } from '@ai-sdk/react';
 import { DefaultChatTransport } from 'ai';
 
 export default function Chat() {
-  const { error, status, sendMessage, messages, reload, stop } = useChat({
+  const { error, status, sendMessage, messages, regenerate, stop } = useChat({
     transport: new DefaultChatTransport({ api: '/mcp/chat' }),
   });
 
@@ -39,7 +39,7 @@ export default function Chat() {
           <button
             type="button"
             className="px-4 py-2 mt-4 text-blue-500 border border-blue-500 rounded-md"
-            onClick={() => reload()}
+            onClick={() => regenerate()}
           >
             Retry
           </button>

examples/next-openai/app/page.tsx

@@ -4,7 +4,7 @@ import { useChat } from '@ai-sdk/react';
 import ChatInput from '@/component/chat-input';
 
 export default function Chat() {
-  const { error, status, sendMessage, messages, reload, stop } = useChat();
+  const { error, status, sendMessage, messages, regenerate, stop } = useChat();
 
   return (
     <div className="flex flex-col w-full max-w-md py-24 mx-auto stretch">
@@ -38,7 +38,7 @@ export default function Chat() {
           <button
             type="button"
             className="px-4 py-2 mt-4 text-blue-500 border border-blue-500 rounded-md"
-            onClick={() => reload()}
+            onClick={() => regenerate()}
           >
             Retry
           </button>

examples/next-openai/app/use-chat-custom-sources/page.tsx

@@ -5,7 +5,7 @@ import { useChat } from '@ai-sdk/react';
 import { DefaultChatTransport } from 'ai';
 
 export default function Chat() {
-  const { error, status, sendMessage, messages, reload, stop } = useChat({
+  const { error, status, sendMessage, messages, regenerate, stop } = useChat({
     transport: new DefaultChatTransport({
       api: '/api/use-chat-custom-sources',
     }),
@@ -60,7 +60,7 @@ export default function Chat() {
           <button
             type="button"
             className="px-4 py-2 mt-4 text-blue-500 border border-blue-500 rounded-md"
-            onClick={() => reload()}
+            onClick={() => regenerate()}
           >
             Retry
           </button>

examples/next-openai/app/use-chat-data-ui-parts/page.tsx

@@ -16,7 +16,7 @@ type MyMessage = UIMessage<
 >;
 
 export default function Chat() {
-  const { error, status, sendMessage, messages, reload, stop } =
+  const { error, status, sendMessage, messages, regenerate, stop } =
     useChat<MyMessage>({
       transport: new DefaultChatTransport({
         api: '/api/use-chat-data-ui-parts',
@@ -84,7 +84,7 @@ export default function Chat() {
           <button
             type="button"
             className="px-4 py-2 mt-4 text-blue-500 border border-blue-500 rounded-md"
-            onClick={() => reload()}
+            onClick={() => regenerate()}
           >
             Retry
           </button>

examples/next-openai/app/use-chat-message-metadata/page.tsx

@@ -8,7 +8,7 @@ import { ExampleMetadata } from '../api/use-chat-message-metadata/example-metada
 type MyMessage = UIMessage<ExampleMetadata>;
 
 export default function Chat() {
-  const { error, status, sendMessage, messages, reload, stop } =
+  const { error, status, sendMessage, messages, regenerate, stop } =
     useChat<MyMessage>({
       transport: new DefaultChatTransport({
         api: '/api/use-chat-message-metadata',
@@ -60,7 +60,7 @@ export default function Chat() {
           <button
             type="button"
             className="px-4 py-2 mt-4 text-blue-500 border border-blue-500 rounded-md"
-            onClick={() => reload()}
+            onClick={() => regenerate()}
           >
             Retry
           </button>

examples/next-openai/app/use-chat-persistence-single-message/[id]/chat.tsx

@@ -14,7 +14,7 @@ export default function Chat({
     transport: new DefaultChatTransport({
       api: '/api/use-chat-persistence-single-message',
       // only send the last message to the server:
-      prepareSubmitMessagesRequest({ messages, id }) {
+      prepareSendMessagesRequest({ messages, id }) {
         return { body: { message: messages[messages.length - 1], id } };
       },
     }),

examples/next-openai/app/use-chat-reasoning/page.tsx

@@ -5,7 +5,7 @@ import { useChat } from '@ai-sdk/react';
 import { DefaultChatTransport } from 'ai';
 
 export default function Chat() {
-  const { error, status, sendMessage, messages, reload, stop } = useChat({
+  const { error, status, sendMessage, messages, regenerate, stop } = useChat({
     transport: new DefaultChatTransport({ api: '/api/use-chat-reasoning' }),
   });
 
@@ -66,7 +66,7 @@ export default function Chat() {
           <button
             type="button"
             className="px-4 py-2 mt-4 text-blue-500 border border-blue-500 rounded-md"
-            onClick={() => reload()}
+            onClick={() => regenerate()}
           >
             Retry
           </button>

examples/next-openai/app/use-chat-resume/chat.tsx

@@ -14,7 +14,7 @@ export function Chat({
   autoResume: boolean;
   initialMessages: UIMessage[];
 }) {
-  const { error, status, sendMessage, messages, reload, stop } = useChat({
+  const { error, status, sendMessage, messages, regenerate, stop } = useChat({
     id,
     messages: initialMessages,
     transport: new DefaultChatTransport({ api: '/api/use-chat-resume' }),
@@ -70,7 +70,7 @@ export function Chat({
           <button
             type="button"
             className="px-4 py-2 mt-4 text-blue-500 border border-blue-500 rounded-md"
-            onClick={() => reload()}
+            onClick={() => regenerate()}
           >
             Retry
           </button>

examples/next-openai/app/use-chat-sources/page.tsx

@@ -5,7 +5,7 @@ import { useChat } from '@ai-sdk/react';
 import { DefaultChatTransport } from 'ai';
 
 export default function Chat() {
-  const { error, status, sendMessage, messages, reload, stop } = useChat({
+  const { error, status, sendMessage, messages, regenerate, stop } = useChat({
     transport: new DefaultChatTransport({ api: '/api/use-chat-sources' }),
   });
 
@@ -58,7 +58,7 @@ export default function Chat() {
           <button
             type="button"
             className="px-4 py-2 mt-4 text-blue-500 border border-blue-500 rounded-md"
-            onClick={() => reload()}
+            onClick={() => regenerate()}
           >
             Retry
           </button>