fix(fork): resolve P0/P1 bugs — protocol, atomicity, streaming guard, button

apps/sim/app/api/mothership/chats/[chatId]/fork/route.ts

@@ -60,6 +60,10 @@ export const POST = withRouteHandler(
         await assertActiveWorkspaceAccess(parent.workspaceId, userId)
       }
 
+      if (parent.conversationId) {
+        return createBadRequestResponse('Cannot fork a chat with an active stream')
+      }
+
       // Find the fork point in the Sim-side messages array.
       const messages = Array.isArray(parent.messages) ? (parent.messages as PersistedMessage[]) : []
       const forkIdx = messages.findIndex((m) => m.id === upToMessageId)
@@ -84,6 +88,7 @@ export const POST = withRouteHandler(
           id: newId,
           userId,
           workspaceId: parent.workspaceId,
+          workflowId: parent.workflowId,
           type: parent.type,
           title,
           model: parent.model,
@@ -103,32 +108,45 @@ export const POST = withRouteHandler(
       }
 
       // Clone copilot-service conversation state (messages, active_messages, memory files).
-      // Best-effort: if the copilot service doesn't have a row for the source chat yet, skip.
+      const copilotHeaders: Record<string, string> = { 'Content-Type': 'application/json' }
+      if (env.COPILOT_API_KEY) {
+        copilotHeaders['x-api-key'] = env.COPILOT_API_KEY
+      }
+      let copilotFailed = false
       try {
-        const copilotHeaders: Record<string, string> = { 'Content-Type': 'application/json' }
-        if (env.COPILOT_API_KEY) {
-          copilotHeaders['x-api-key'] = env.COPILOT_API_KEY
-        }
         const copilotRes = await fetchGo(`${SIM_AGENT_API_URL}/api/chats/fork`, {
           method: 'POST',
           headers: copilotHeaders,
           body: JSON.stringify({
             sourceChatId: chatId,
             newChatId: newId,
-            upToMessageId,
+            keepCount: forkedMessages.length,
             userId,
           }),
           spanName: 'sim → go /api/chats/fork',
           operation: 'fork_chat',
         })
         if (!copilotRes.ok) {
           const text = await copilotRes.text().catch(() => '')
-          logger.warn('Copilot fork returned non-OK', { status: copilotRes.status, body: text })
+          logger.error('Copilot fork returned non-OK', { status: copilotRes.status, body: text })
+          copilotFailed = true
         }
       } catch (err) {
-        // The copilot service may not have a row for this chat if no messages
-        // have been sent yet, or if it's unreachable. Log and continue.
-        logger.warn('Failed to fork copilot-service conversation, skipping', { err })
+        logger.error('Failed to call copilot fork endpoint', { err })
+        copilotFailed = true
+      }
+
+      if (copilotFailed) {
+        // Compensating delete — remove the orphaned Sim row.
+        await db
+          .delete(copilotChats)
+          .where(eq(copilotChats.id, newId))
+          .catch((e: unknown) => {
+            logger.error('Failed to delete orphaned forked chat after copilot failure', {
+              error: e,
+            })
+          })
+        return createInternalServerErrorResponse('Failed to fork chat')
       }
 
       if (newChat.workspaceId) {

apps/sim/app/workspace/[workspaceId]/components/message-actions/message-actions.tsx

@@ -55,6 +55,7 @@ interface MessageActionsProps {
   userQuery?: string
   requestId?: string
   messageId?: string
+  isStreamActive?: boolean
 }
 
 export const MessageActions = memo(function MessageActions({
@@ -63,6 +64,7 @@ export const MessageActions = memo(function MessageActions({
   userQuery,
   requestId,
   messageId,
+  isStreamActive,
 }: MessageActionsProps) {
   const router = useRouter()
   const params = useParams<{ workspaceId: string }>()
@@ -164,7 +166,7 @@ export const MessageActions = memo(function MessageActions({
 
   const hasContent = Boolean(content)
   const canSubmitFeedback = Boolean(chatId && userQuery)
-  const canFork = false
+  const canFork = Boolean(messageId && !isStreamActive)
   if (!hasContent && !canSubmitFeedback && !canFork) return null
 
   return (

apps/sim/app/workspace/[workspaceId]/home/components/mothership-chat/mothership-chat.tsx

@@ -220,6 +220,7 @@ export function MothershipChat({
                         userQuery={precedingUserContent}
                         requestId={msg.requestId}
                         messageId={msg.id}
+                        isStreamActive={isStreamActive}
                       />
                     </div>
                   )}