fix(frontend): keep entity and message deletes in sync

frontend/src/__tests__/pages/EditTaskPage.test.tsx

@@ -294,6 +294,45 @@ describe('EditTaskPage', () => {
     })
   })
 
+  it('should_removeOnlyDeletedGeneratedMessage_when_deleteSucceedsWithoutRefetch', async () => {
+    persistedHistory = [
+      {
+        id: 'message-2',
+        taskId: 'task-1',
+        label: 'Message #2',
+        content: 'SUBJECT: Second\nBODY:\nSecond output',
+        createdAt: '2026-03-27T12:10:00Z',
+      },
+      {
+        id: 'message-1',
+        taskId: 'task-1',
+        label: 'Message #1',
+        content: 'SUBJECT: First\nBODY:\nFirst output',
+        createdAt: '2026-03-27T12:00:00Z',
+      },
+    ]
+    vi.mocked(tasksApi.getTaskGeneratedMessages).mockResolvedValue(persistedHistory)
+    vi.mocked(tasksApi.deleteTaskGeneratedMessage).mockResolvedValue(undefined)
+
+    renderPage()
+
+    const secondMessageHistoryItem = await screen.findByRole('button', { name: /^message #2$/i })
+    expect(await screen.findByRole('button', { name: /^message #1$/i })).toBeInTheDocument()
+
+    fireEvent.click(
+      screen.getByRole('button', {
+        name: /delete message #1/i,
+      })
+    )
+
+    await waitFor(() => {
+      expect(tasksApi.deleteTaskGeneratedMessage).toHaveBeenCalledWith('task-1', 'message-1')
+      expect(screen.queryByRole('button', { name: /^message #1$/i })).not.toBeInTheDocument()
+      expect(secondMessageHistoryItem).toBeInTheDocument()
+      expect(screen.getByText(/Second output/i)).toBeInTheDocument()
+    })
+  })
+
   it('should_loadPersistedGeneratedMessageHistory_when_pageLoads', async () => {
     persistedHistory = [
       {