[Service Bus] Fix batch send of messages with routing properties

[EldertGrootenboer]

Problem

Sending a batch of messages with message_id, session_id, or
partition_key set on the first message raised
TypeError: 'BatchMessage' object is not subscriptable under the uamqp
transport (uamqp_transport=True), and surfaced a secondary
AttributeError: 'list' object has no attribute '_message' on the list send
path. Regression from #42598.

Root cause: ServiceBusMessageBatch._add captured the batch-envelope
message_id/session_id properties and partition_key annotation by calling
the module-level pyamqp helpers (set_message_properties /
set_message_annotations) unconditionally, regardless of the active transport.
Those helpers index the message as a list (message[3], message[2]). Under
uamqp the batch envelope is a BatchMessage (not subscriptable), so the
capture raised TypeError.

One root cause, two symptoms:

• Batch-object path (create_message_batch() + add_message()): the
  TypeError surfaces directly.
• List path (send_messages([...])): the sender builds a batch via
  _from_list() -> _add(); the same TypeError was then swallowed by a
  broad except TypeError (intended to detect "not a list"), which went on to
  do obj_message._message = ... on the list, producing the reported secondary
  AttributeError.

Under uamqp the outgoing transform auto-assigns a message_id, so even a bare
ServiceBusMessage(b"x") in a batch triggered the crash.

Fix

• Move batch-envelope property capture behind a new transport method,
  set_batch_envelope_properties(batch_message, message_id, session_id, partition_key), with separate pyamqp and uamqp implementations. The pyamqp
  implementation preserves the existing list-indexed behavior; the uamqp
  implementation sets batch_message.properties = MessageProperties(...) plus
  the partition-key annotation. It is a no-op when all three are falsy and runs
  once per batch.
• Call it once per batch from _common/message.py (guarded by
  self._count == 1), and drop the now-unused unconditional pyamqp import.
• Replace the broad except TypeError in the sync and async senders with an
  explicit isinstance(obj_message, list) check, so a genuine TypeError
  raised while building the batch is no longer masked.
  transform_outbound_messages returns a list for iterable input and a single
  ServiceBusMessage otherwise, so the discrimination is behavior-equivalent
  for valid inputs.

Routing-property mapping is consistent with the other Azure SDK languages:
session_id maps to the AMQP group-id, partition_key to the
x-opt-partition-key annotation.

Testing

Added unit coverage in tests/test_message.py:

• test_set_batch_envelope_properties exercises each branch (no-op,
  message_id only, session_id only, partition_key only) on both transports.
• strengthened test_servicebus_message_batch to assert the envelope
  properties and annotations on both transports.
• test_transform_outbound_messages_discriminates_list_vs_single pins the
  list-vs-single contract the sender discrimination relies on.

Result (Python 3.12): targeted run 5 passed. Batch and send behavior across
both transports is additionally covered by the live test_queues /
test_queues_async suites.

What changed

• sdk/servicebus/azure-servicebus/azure/servicebus/_transport/_base.py
• sdk/servicebus/azure-servicebus/azure/servicebus/_transport/_pyamqp_transport.py
• sdk/servicebus/azure-servicebus/azure/servicebus/_transport/_uamqp_transport.py
• sdk/servicebus/azure-servicebus/azure/servicebus/_common/message.py
• sdk/servicebus/azure-servicebus/azure/servicebus/_servicebus_sender.py
• sdk/servicebus/azure-servicebus/azure/servicebus/aio/_servicebus_sender_async.py
• sdk/servicebus/azure-servicebus/tests/test_message.py
• sdk/servicebus/azure-servicebus/CHANGELOG.md

[Copilot]

Pull request overview

This PR fixes a regression (from #42598) where sending a batch of Service Bus messages whose first message carried a message_id, session_id, or partition_key crashed under the uamqp transport with TypeError: 'BatchMessage' object is not subscriptable, plus a masked secondary AttributeError on the list-send path. The root cause was that ServiceBusMessageBatch._add captured batch-envelope routing properties by calling pyamqp-specific helpers (set_message_properties / set_message_annotations) unconditionally, which index the message as a list — invalid for a uamqp BatchMessage.

The fix introduces a transport-abstraction method set_batch_envelope_properties() (abstract in _base.py, implemented separately for pyamqp and uamqp), routes the capture through it, and replaces the broad except TypeError in both senders with an explicit isinstance(obj_message, list) discriminator so genuine TypeErrors are no longer swallowed.

Changes:

• Added a transport-specific set_batch_envelope_properties() hook and wired ServiceBusMessageBatch._add to call it, removing the unconditional pyamqp import.
• Replaced try/except TypeError discrimination with an explicit list check in the sync and async senders.
• Added unit coverage (per-branch envelope-property capture on both transports, batch-envelope assertions, and a list-vs-single discriminator contract test) plus a CHANGELOG entry.

I verified: imports are correct on every touched module (List/Optional/cast in pyamqp, MessageProperties/BatchMessage/_X_OPT_PARTITION_KEY at runtime in uamqp), the removed set_message_properties/set_message_annotations imports are no longer referenced in message.py while _X_OPT_PARTITION_KEY is still used, the pyamqp Properties indices (message_id=0, group_id=10) are correct, the pyamqp batch envelope is a plain list (subscriptable) while uamqp uses BatchMessage, ServiceBusMessageBatch inputs are handled before the new discriminator, and transform_outbound_messages returns a list vs single message consistent with the new check. I found no concrete issues to comment on.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
azure/servicebus/_transport/_base.py	Adds the abstract set_batch_envelope_properties to the transport interface, following the existing @staticmethod @abstractmethod pattern.
azure/servicebus/_transport/_pyamqp_transport.py	Implements the hook preserving the list-indexed pyamqp behavior (Properties index 0/10, partition-key annotation).
azure/servicebus/_transport/_uamqp_transport.py	Implements the hook for uamqp via MessageProperties and the partition-key annotation, fixing the crash.
azure/servicebus/_common/message.py	Routes batch-envelope capture through the transport hook and drops the now-unused unconditional pyamqp import.
azure/servicebus/_servicebus_sender.py	Replaces broad except TypeError with an explicit isinstance(..., list) discriminator.
azure/servicebus/aio/_servicebus_sender_async.py	Mirrors the sync sender discrimination change.
tests/test_message.py	Adds per-branch and discriminator unit tests; strengthens existing batch test on both transports.
CHANGELOG.md	Documents the regression fix under 7.14.4 (Unreleased).