infrastructure-request-validation-d-when-early-validation-failures-in-http-request-han-4216f0b6

THEN Add an explicit asynchronous sleep (e.g., await asyncio.sleep(0.1)) before returning from request validation functions like _handle_post_request to allow the message router task to finish its checkpoint.

async def _handle_post_request(self, scope, request, receive, send):
    # ... validation ...
    if not (has_json and has_sse):
        response = self._create_error_response(...)
        await response(scope, receive, send)
        await asyncio.sleep(0.1)  # Allow message_router to complete checkpoint
        return