fix: RabbitMQ 4.3.0 compatibility

[Nusnus]

Summary

RabbitMQ 4.3.0 disables transient non-exclusive queues by default. Kombu's pidbox queues and SimpleBuffer queues are declared with durable=False, exclusive=False, which RabbitMQ 4.3.0 rejects with (541) INTERNAL_ERROR.

RabbitMQ References

• Release Notes (Broadcom TechDocs): "Deprecated Features are Now Disabled by Default — This includes non-durable (transient) non-exclusive queues: attempts to declare a queue with that property combination are rejected by default. Use durable queues, transient exclusive queues, or durable queues with a queue TTL instead."
• Deprecated Features List: transient_nonexcl_queues — "Covers queues that are both non-durable and non-exclusive, this combination should be avoided. Use durable queues or non-durable exclusive queues."
• Deprecation Announcement (August 2021): Original deprecation notice for RabbitMQ 4.0+

Fix

kombu/pidbox.py — Change Mailbox default from queue_exclusive=False to queue_exclusive=True. Pidbox queues are per-connection, transient control channels — only the declaring connection consumes from them. Messages are published as transient (the exchange sets delivery_mode='transient' in _get_exchange()), so a durable queue surviving a restart would just leave an empty queue that never auto-deletes, accumulating zombie queues in containerized deployments. exclusive=True matches the intended lifecycle and is RabbitMQ's recommended alternative for the deprecated pattern.

Additionally, Node.Consumer now catches channel errors (e.g., RESOURCE_LOCKED) and raises InconsistencyError with the W_PIDBOX_IN_USE guidance message. With exclusive queues, the existing verify_exclusive / on_declared soft-check can't fire (the broker rejects the declare before the callback runs), so this hardens the duplicate-node detection into a proper error.

kombu/simple.py — Add 'exclusive': True to SimpleBuffer.queue_opts. SimpleBuffer is documented as "Simple API for ephemeral queues" with durable=False, auto_delete=True — exclusive=True matches this ephemeral semantics exactly.

Before → After

	Before	After
Mailbox.queue_exclusive default	False	True
SimpleBuffer.queue_opts	{'durable': False, 'auto_delete': True}	{'durable': False, 'auto_delete': True, 'exclusive': True}
Duplicate node detection	W_PIDBOX_IN_USE warning via on_declared callback	InconsistencyError with W_PIDBOX_IN_USE message

Why exclusive=True (not durable=True)

• Pidbox messages are transient (exchange delivery_mode='transient') — a durable queue surviving a restart just leaves an empty queue
• durable=True disables auto_delete (auto_delete = not self.queue_durable), causing permanent zombie queues in k8s/ECS where each pod gets a unique nodename
• The pidbox lifecycle is a natural fit for exclusive queues: one connection declares it, only that connection consumes, the queue dies with its consumer
• exclusive=True implies auto_delete=True per AMQP spec (enforced in entity.py:594-596)
• The ValueError guard at pidbox.py:202-206 prevents the invalid durable=True + exclusive=True combination

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Companion PR: celery/celery#10290 | Closes #2237

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.50%. Comparing base (339fb58) to head (08eacaa).
✅ All tests successful. No failed tests found.

Additional details and impacted files

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##             main    #2531   +/-   ##
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  Coverage   82.49%   82.50%           
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  Files          79       79           
  Lines       10190    10195    +5     
  Branches     1170     1170           
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+ Hits         8406     8411    +5     
  Misses       1582     1582           
  Partials      202      202           

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[Nusnus]

CI pass, nice

[Copilot]

Pull request overview

Updates Kombu’s pidbox and SimpleBuffer queue declarations to avoid RabbitMQ 4.3.0’s default rejection of transient non-exclusive queues, and adjusts tests/docs accordingly.

Changes:

• Default pidbox (Mailbox) queues to exclusive=True and convert certain channel-level declare failures into an InconsistencyError.
• Default SimpleBuffer queues to exclusive=True to preserve ephemeral semantics while remaining compatible with RabbitMQ 4.3.0.
• Update unit tests and pidbox reference docs to reflect the new defaults/behavior.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
kombu/pidbox.py	Default pidbox queues to exclusive; add channel-error handling that raises InconsistencyError.
kombu/simple.py	Make SimpleBuffer queues exclusive by default.
t/unit/test_pidbox.py	Add/adjust tests for exclusive-default pidbox queues and channel-error behavior.
t/unit/test_simple.py	Update tests to assert SimpleBuffer default exclusivity and override behavior.
docs/reference/kombu.pidbox.rst	Document queue_durable / queue_exclusive options and the new default.

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[Copilot]

The except channel_errors block converts any channel-level broker failure into InconsistencyError with the “node already using” guidance. channel_errors typically includes cases like ACCESS_REFUSED, PRECONDITION_FAILED, etc., so this can produce a misleading error message and hide the underlying cause. Consider only translating known “exclusive queue already in use” failures (e.g., RESOURCE_LOCKED / specific reply code or exception type), and re-raise other channel errors (or at least include the original exception details in the raised error).

[auvipy]

@Nusnus bro can you cross check this, please?