Receiver does not ack/nack Tasks that can't be found

[anjafr]

Taskiq version

0.11.17

Python version

Python 3.11

OS

macOS

What happened?

When encountering a task/a message that can't be found, the TaskIQ receiver logs a warning and then returns (None), see receiver.py
However, this leaves the task/message unacked and forever pending in limbo.
Clearly, if the task can't be found this is not going anywhere and either the broker and/or the result backend should in one way or another be informed.
In our case: we use RabbitMQ as broker and had a handful of "not found" tasks (the reason has been fixed, doesn't really matter) around. They were no longer in queue (due to pre-fetch), so inspecting the message queue or purging it did not help. Terminating the consumer only put those messages back into the queue very briefly, before the re-spawned consumer picked them up again and nothing was gained. (For RabbitMQ specifically, these messages should have been nacked. )
Independent of the exact broker and implementation however this behaviour is problematic: it leaves messages in an undefined state.

Relevant log output

WARNING:receiver.py:119:    task "project:dont_ask_me_how_this_happened_task" is not found. Maybe you forgot to import it?

Broker initialization code

broker = AioPikaBroker(
        url=broker_config.to_url(
            vhost=app_config.name
        ),
        queue_name=app_config.name,
        delayed_message_exchange_plugin=True,
        max_priority=5,
        qos=3,
    )