fix(chat): detect aborts by signal state, not error identity

fetch rejects with the RAW abort reason when its signal carries one —
abort('unmount:client_cleanup') surfaces as a plain string, so every
err.name === 'AbortError' check missed it and the restore path never ran
(verified live). The test stub now rejects with the raw reason like real
fetch, which turns this gap red.

Author: j15z

apps/sim/app/workspace/[workspaceId]/home/hooks/use-chat.mount-send.test.tsx

@@ -51,12 +51,6 @@ function emptySseResponse(): Response {
   return new Response(stream, { status: 200, headers: { 'Content-Type': 'text/event-stream' } })
 }
 
-function abortError(): Error {
-  const error = new Error('Aborted')
-  error.name = 'AbortError'
-  return error
-}
-
 async function fetchStub(input: RequestInfo | URL, init?: RequestInit): Promise<Response> {
   const url = String(input instanceof Request ? input.url : input)
 
@@ -66,11 +60,13 @@ async function fetchStub(input: RequestInfo | URL, init?: RequestInit): Promise<
     return new Promise<Response>((_, reject) => {
       const signal = init?.signal
       if (!signal) return
+      // Real fetch rejects with the RAW abort reason (a string here), not an
+      // AbortError — the regression this suite guards depends on that shape.
       if (signal.aborted) {
-        reject(abortError())
+        reject(signal.reason)
         return
       }
-      signal.addEventListener('abort', () => reject(abortError()), { once: true })
+      signal.addEventListener('abort', () => reject(signal.reason), { once: true })
     })
   }
 

apps/sim/app/workspace/[workspaceId]/home/hooks/use-chat.ts

@@ -3833,7 +3833,12 @@ export function useChat(
           }
         }
       } catch (err) {
-        if (err instanceof Error && err.name === 'AbortError') {
+        /* fetch rejects with the RAW abort reason (here a plain string) when
+           its signal was aborted with abort(reason) — an `err.name` check alone
+           misses those, so abort detection also consults the signal itself. */
+        const sendWasAborted =
+          (err instanceof Error && err.name === 'AbortError') || sendAbortSignal?.aborted === true
+        if (sendWasAborted) {
           if (sendAbortSignal?.reason === 'unmount:client_cleanup' && !sendReachedServer) {
             /* The mount-settling effect cycle (Suspense hide/reveal) ran the
                unmount cleanup while this send was still pre-dispatch. Nothing