fix(chat): deliver an aborted chatless send to the live replacement surface

The settling remount's consumer checks handoff storage before the
restore microtask re-persists it, so the stored handoff sat unread until
a navigation. The replacement surface's send listener IS registered by
restore time — deliver the message directly through the claimable send
event, keeping the stored handoff as the no-surface fallback.

Author: j15z

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

@@ -143,6 +143,31 @@ describe('useChat mount-settling send recovery', () => {
     vi.clearAllMocks()
   })
 
+  it('delivers an aborted chatless send directly to a live replacement surface', async () => {
+    const received: string[] = []
+    const claim = (event: Event) => {
+      received.push((event as CustomEvent<{ message: string }>).detail.message)
+      event.preventDefault()
+    }
+    window.addEventListener('mothership-send-message', claim)
+
+    try {
+      const { getResult, unmount } = renderUseChat()
+      await act(async () => {
+        void getResult().sendMessage('hello from the palette')
+      })
+      await waitFor(() => state.postCalls === 1)
+
+      unmount()
+      await waitFor(() => received.length === 1)
+
+      expect(received).toEqual(['hello from the palette'])
+      expect(window.localStorage.getItem('sim_mothership_handoff')).toBeNull()
+    } finally {
+      window.removeEventListener('mothership-send-message', claim)
+    }
+  })
+
   it('re-persists an aborted chatless send as a handoff for the next mount', async () => {
     const { getResult, unmount } = renderUseChat()
 

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

@@ -92,6 +92,7 @@ import {
   migrateDesktopChatScopes,
   PENDING_CHAT_KEY_PREFIX,
 } from '@/lib/desktop/chat-scope'
+import { sendMothershipMessage } from '@/lib/mothership/events'
 import { initTerminalTransport } from '@/lib/terminal/transport'
 import { getQueryClient } from '@/app/_shell/providers/get-query-client'
 import { useFilePreviewController } from '@/app/workspace/[workspaceId]/home/hooks/preview'
@@ -4518,13 +4519,19 @@ export function useChat(
           dispatchChatKey.startsWith(PENDING_CHAT_KEY_PREFIX) &&
           !msg.fileAttachments?.length
         ) {
-          MothershipHandoffStorage.store(
-            {
-              message: msg.content,
-              ...(msg.contexts?.length ? { contexts: msg.contexts } : {}),
-            },
-            workspaceId
-          )
+          /* The settling remount has already run its mount effects by the time
+             this microtask executes, so the replacement surface's send listener
+             is live — deliver directly. The stored-handoff fallback covers a
+             real navigation away, where the next mount's consumer picks it up. */
+          if (!sendMothershipMessage(msg.content, msg.contexts)) {
+            MothershipHandoffStorage.store(
+              {
+                message: msg.content,
+                ...(msg.contexts?.length ? { contexts: msg.contexts } : {}),
+              },
+              workspaceId
+            )
+          }
           return
         }
         useMothershipQueueStore.getState().insertAt(dispatchChatKey, originalIndex, msg)