AMQP producers: emit message_annotations from manifest (needed for x-opt-partition-key on Service Bus / Event Hubs)

[clemensv]

Summary

The Python AMQP producer template (xrcg/templates/py/amqpproducer) currently reads protocoloptions.properties (AMQP message-properties section) and protocoloptions.application_properties (AMQP application-properties section), but does not emit anything for the AMQP message-annotations section.

Result: manifests cannot declare partition keys that reach the broker.

Why this matters

For Azure Service Bus and Azure Event Hubs, partition routing is driven entirely by the annotation b"x-opt-partition-key" in the AMQP message-annotations section. Confirmed in the Microsoft Python SDKs:

• azure/servicebus/_common/constants.py:119 -> _X_OPT_PARTITION_KEY = b"x-opt-partition-key"
• azure/servicebus/_common/message.py:331 -> self._set_message_annotations(_X_OPT_PARTITION_KEY, value) (string, max 128 chars)
• azure/eventhub/_constants.py:10 -> PROP_PARTITION_KEY = b"x-opt-partition-key"
• azure/eventhub/_transport/_pyamqp_transport.py:393 -> annotations[PROP_PARTITION_KEY] = partition_key

Without xrcg emitting this annotation, downstream feeders either lose partition ordering or have to monkey-patch the generated _sender.send from the bridge.

Requested change

Extend the AMQP producer template to read a new section protocoloptions.message_annotations (peer to properties and application_properties):

• For each entry whose value is a uritemplate, accept the corresponding _<placeholder> kwarg on send_* / send_*_batch.
• Emit ann[b"<name>"] = "<expanded>" and assign to amqp_msg.annotations. Symbol-typed keys must be encoded as bytes per the AMQP 1.0 spec - Service Bus / Event Hubs reject string keys.
• For x-opt-partition-key specifically: enforce string value, truncate to 128 chars on encode (Service Bus MESSAGE_PROPERTY_MAX_LENGTH).

Same change should land in the C#, Java, and TypeScript AMQP producer templates for parity.

Repo impact

Blocks the amqp-feeder skill default partition-key recipe in clemensv/real-time-sources. Pegelonline currently ships a bridge-side monkey-patch workaround documented in stream-bridge-implementation; we want to drop it as soon as the template supports annotations natively.