fix(chat): delete trailing messages before regenerate using transportChatId

components/VercelChat/message-editor.tsx

@@ -9,8 +9,8 @@ import { useVercelChatContext } from "@/providers/VercelChatProvider";
 import { TextUIPart, UIMessage } from "ai";
 
 export function MessageEditor({ message, setMode }: EditingMessageProps) {
-  const { id, setMessages, reload } = useVercelChatContext();
-  if (!id) {
+  const { transportChatId, setMessages, reload } = useVercelChatContext();
+  if (!transportChatId) {
     throw new Error("MessageEditor requires an active chat id");
   }
   const text = (message.parts[0] as TextUIPart)?.text || "";
@@ -31,7 +31,7 @@ export function MessageEditor({ message, setMode }: EditingMessageProps) {
         });
         setMode("view");
         if (text !== draftContent) {
-          reload();
+          void reload({ skipTrailingDelete: true });
         }
       },
     });
@@ -83,7 +83,7 @@ export function MessageEditor({ message, setMode }: EditingMessageProps) {
           disabled={isDeletingTrailingMessages}
           onClick={() => {
             void deleteTrailingMessages({
-              chatId: id,
+              chatId: transportChatId,
               fromMessageId: message.id,
             });
           }}

hooks/reloadOptions.ts

@@ -0,0 +1,5 @@
+/** Options for {@link useVercelChat}'s reload (retry / edit-and-resubmit). */
+export type ReloadOptions = {
+  /** When true, skip server trailing delete (caller already deleted). */
+  skipTrailingDelete?: boolean;
+};

hooks/useVercelChat.ts

@@ -21,6 +21,11 @@ import { usePrivy } from "@privy-io/react-auth";
 import { TextAttachment } from "@/types/textAttachment";
 import { formatTextAttachments } from "@/lib/chat/formatTextAttachments";
 import { useDeleteTrailingMessages } from "./useDeleteTrailingMessages";
+import {
+  deleteTrailingMessages as deleteTrailingMessagesApi,
+  TrailingDeleteError,
+} from "@/lib/messages/deleteTrailingMessages";
+import type { ReloadOptions } from "./reloadOptions";
 import { getFileContents } from "@/lib/sandboxes/getFileContents";
 import getMimeFromPath from "@/lib/files/getMimeFromPath";
 import { getChatPath } from "@/lib/chat/getChatPath";
@@ -301,14 +306,57 @@ export function useVercelChat({
     sendMessage(message, { body: chatRequestBody, headers });
   };
 
-  const handleReload = useCallback(async () => {
+  const handleReload = useCallback(async (options?: ReloadOptions) => {
     const headers = await getHeaders();
-    // Retry/Edit (MessageParts + message-editor) call reload() → regenerate,
-    // bypassing handleSubmit; persist the selected model first so the
-    // regenerated turn bills it, not the previous/default model.
+    // MessageParts Retry calls reload() to delete the assistant tail then
+    // regenerate. MessageEditor already deleted trailing server-side and
+    // passes skipTrailingDelete (messages state may still list the assistant).
     await persistSelectedModel();
+
+    if (!options?.skipTrailingDelete) {
+      const lastMessage = messages.at(-1);
+      if (lastMessage?.role === "assistant") {
+        const accessToken = await getAccessToken();
+        if (!accessToken) {
+          toast.error("Please sign in to regenerate.");
+          return;
+        }
+
+        try {
+          await deleteTrailingMessagesApi({
+            chatId: transportChatId,
+            fromMessageId: lastMessage.id,
+            accessToken,
+          });
+        } catch (error) {
+          // Boundary already removed (e.g. race) — still regenerate.
+          if (
+            error instanceof TrailingDeleteError &&
+            error.status === 404
+          ) {
+            // no-op
+          } else {
+            console.error(
+              "Failed to delete trailing messages before regenerate:",
+              error,
+            );
+            toast.error("Failed to regenerate. Please try again.");
+            return;
+          }
+        }
+      }
+    }
+
     await regenerate({ body: chatRequestBody, headers });
-  }, [getHeaders, regenerate, chatRequestBody, persistSelectedModel]);
+  }, [
+    getHeaders,
+    getAccessToken,
+    regenerate,
+    chatRequestBody,
+    persistSelectedModel,
+    messages,
+    transportChatId,
+  ]);
 
   // Keep messagesRef in sync with messages
   messagesLengthRef.current = messages.length;
@@ -344,7 +392,7 @@ export function useVercelChat({
 
     if (earliestFailedUserMessageId) {
       await deleteTrailingMessages({
-        chatId: id,
+        chatId: transportChatId,
         fromMessageId: earliestFailedUserMessageId,
       });
     }
@@ -403,6 +451,7 @@ export function useVercelChat({
   return {
     // States
     messages,
+    transportChatId,
     status,
     input,
     isLoading,

lib/messages/deleteTrailingMessages.ts

@@ -1,5 +1,15 @@
 import { getClientApiBaseUrl } from "@/lib/api/getClientApiBaseUrl";
 
+export class TrailingDeleteError extends Error {
+  readonly status: number;
+
+  constructor(message: string, status: number) {
+    super(message);
+    this.name = "TrailingDeleteError";
+    this.status = status;
+  }
+}
+
 /**
  * Deletes trailing messages in a chat from a given message ID onward.
  */
@@ -24,6 +34,9 @@ export async function deleteTrailingMessages({
   );
 
   if (!response.ok) {
-    throw new Error("Failed to delete trailing messages");
+    throw new TrailingDeleteError(
+      "Failed to delete trailing messages",
+      response.status,
+    );
   }
 }

providers/VercelChatProvider.tsx

@@ -14,10 +14,13 @@ import { useArtistProvider } from "./ArtistProvider";
 import { GatewayLanguageModelEntry } from "@ai-sdk/gateway";
 import { TextAttachment } from "@/types/textAttachment";
 import type { WorkspaceStatus } from "@/components/VercelChat/WorkspaceStatusIndicator";
+import type { ReloadOptions } from "@/hooks/reloadOptions";
 
 // Interface for the context data
 interface VercelChatContextType {
   id: string | undefined;
+  /** Api-facing chat id (`workflowChatId ?? id`) for recoup-api calls. */
+  transportChatId: string;
   sessionId: string | undefined;
   messages: UIMessage[];
   availableModels: GatewayLanguageModelEntry[];
@@ -31,7 +34,7 @@ interface VercelChatContextType {
   setInput: (input: string) => void;
   input: string;
   setMessages: UseChatHelpers<UIMessage>["setMessages"];
-  reload: () => void;
+  reload: (options?: ReloadOptions) => Promise<void>;
   append: (message: UIMessage) => void;
   attachments: FileUIPart[];
   pendingAttachments: FileUIPart[];
@@ -114,6 +117,7 @@ export function VercelChatProvider({
   // Use the useVercelChat hook to get the chat state and functions
   const {
     messages,
+    transportChatId,
     status,
     isLoading,
     hasError,
@@ -138,9 +142,10 @@ export function VercelChatProvider({
     textAttachments,
   });
 
-  const reload = useCallback(() => {
-    return originalReload();
-  }, [originalReload]);
+  const reload = useCallback(
+    (options?: ReloadOptions) => originalReload(options),
+    [originalReload],
+  );
 
   // When a message is sent successfully, clear the attachments
   const handleSendMessageWithClear = async (
@@ -155,6 +160,7 @@ export function VercelChatProvider({
   // Create the context value object
   const contextValue: VercelChatContextType = {
     id: chatId,
+    transportChatId,
     sessionId,
     messages,
     model,