fix(chats): stop reading a deleted chat while its view is still mounted

Removing the detail entry under a live observer rebuilt it on the next render
and fetched the chat that was just deleted: a 404 and a load error until the
navigation landed. Cancel what is in flight and remove the entry when its last
reader leaves.

Author: waleedlatif1

apps/sim/hooks/queries/mothership-chats.test.ts

@@ -27,6 +27,8 @@ vi.mock('@/lib/terminal/transport', () => ({
 import type { MothershipEffort } from '@/lib/mothership/model-options'
 import {
   fetchMothershipChatHistory,
+  mothershipChatHistoryQueryOptions,
+  useDeleteMothershipChat,
   useDeleteMothershipChats,
   useSetMothershipChatEffort,
 } from '@/hooks/queries/mothership-chats'
@@ -101,6 +103,46 @@ describe('tasks query boundary parsing', () => {
     })
   })
 
+  it('reads a deleted chat no more while a view holds it, and forgets it once the view leaves', async () => {
+    const tanstack =
+      await vi.importActual<typeof import('@tanstack/react-query')>('@tanstack/react-query')
+    const client = new tanstack.QueryClient()
+    reactQueryMockFns.mockUseQueryClient.mockReturnValueOnce(
+      client as unknown as typeof queryClient
+    )
+    const mutation = useDeleteMothershipChat({ organizationId: 'org-1' }) as unknown as {
+      onSuccess: (data: undefined, chatId: string) => Promise<void>
+    }
+    const options = mothershipChatHistoryQueryOptions('chat-open')
+    vi.mocked(fetch).mockResolvedValueOnce(
+      jsonResponse({
+        success: true,
+        chat: {
+          id: 'chat-open',
+          title: null,
+          mode: 'assistant',
+          messages: [],
+          activeStreamId: null,
+          resources: [],
+        },
+      })
+    )
+    await client.prefetchQuery(options)
+    vi.mocked(fetch).mockClear()
+    const view = new tanstack.QueryObserver(client, options)
+    const leave = view.subscribe(() => {})
+
+    await mutation.onSuccess(undefined, 'chat-open')
+    view.getOptimisticResult(client.defaultQueryOptions(options))
+    view.setOptions(options)
+
+    expect(fetch).not.toHaveBeenCalled()
+    expect(view.getCurrentResult().isSuccess).toBe(true)
+    leave()
+    expect(client.getQueryCache().find({ queryKey: options.queryKey })).toBeUndefined()
+    client.clear()
+  })
+
   it('loads a chat from a server that predates the effort field', async () => {
     vi.mocked(fetch).mockResolvedValueOnce(
       jsonResponse({

apps/sim/hooks/queries/mothership-chats.ts

@@ -516,6 +516,28 @@ async function deleteChat(chatId: string): Promise<void> {
   })
 }
 
+/**
+ * Forgets a deleted chat's transcript. Removing an entry a mounted view still reads makes its next
+ * render rebuild the entry and read a chat that is gone, so that view keeps what it has until its
+ * last reader leaves, which leaving the deleted chat is about to do.
+ */
+function forgetChatHistory(queryClient: QueryClient, chatId: string) {
+  const queryKey = mothershipChatKeys.detail(chatId)
+  const cache = queryClient.getQueryCache()
+  const query = cache.find({ queryKey, exact: true })
+  if (!query?.getObserversCount()) {
+    queryClient.removeQueries({ queryKey })
+    return
+  }
+  void queryClient.cancelQueries({ queryKey, exact: true })
+  const unsubscribe = cache.subscribe((event) => {
+    if (event.type !== 'observerRemoved' || event.query !== query) return
+    if (query.getObserversCount() > 0) return
+    unsubscribe()
+    queryClient.removeQueries({ queryKey })
+  })
+}
+
 /**
  * Soft-deletes a mothership chat and invalidates both the active and archived
  * chat lists — the chat moves from the sidebar into Recently Deleted.
@@ -526,7 +548,7 @@ export function useDeleteMothershipChat(owner?: MothershipChatOwner) {
     mutationFn: deleteChat,
     onSuccess: async (_data, chatId) => {
       await suspendDesktopChatScopes(chatId)
-      queryClient.removeQueries({ queryKey: mothershipChatKeys.detail(chatId) })
+      forgetChatHistory(queryClient, chatId)
       useMothershipQueueStore.getState().clearChat(chatId)
     },
     onSettled: () => {
@@ -575,7 +597,7 @@ export function useDeleteMothershipChats(owner?: MothershipChatOwner) {
         chatIds.map(async (chatId) => {
           await deleteChat(chatId)
           await suspendDesktopChatScopes(chatId)
-          queryClient.removeQueries({ queryKey: mothershipChatKeys.detail(chatId) })
+          forgetChatHistory(queryClient, chatId)
           useMothershipQueueStore.getState().clearChat(chatId)
         })
       )