[mqtt] Wire MqttIO into Python xlang wrapper generation

Adds name overrides for the new MqttIO SchemaTransforms in
standard_expansion_services.yaml so the generated Python wrappers follow
the kafka-style naming (ReadFromMqtt / WriteToMqtt) and become available
under apache_beam.io.

Regenerates standard_external_transforms.yaml via
:sdks:python:generateExternalTransformsConfig — the file now includes the
mqtt_read:v1 and mqtt_write:v1 entries with their inferred Row schema for
ConnectionConfiguration and the transform descriptions.

Adds an I/Os entry in CHANGES.md for the 2.75.0 release covering both batch
and streaming.

Author: tkaymak

CHANGES.md

@@ -66,6 +66,7 @@
 ## I/Os
 
 * Support for X source added (Java/Python) ([#X](https://github.com/apache/beam/issues/X)).
+* MqttIO: portable `ReadFromMqtt` / `WriteToMqtt` transforms now available in Python via cross-language (`apache_beam.io`), for both batch and streaming ([#32385](https://github.com/apache/beam/issues/32385)).
 
 ## New Features / Improvements
 

sdks/standard_expansion_services.yaml

@@ -44,6 +44,10 @@
       name: 'WriteToKafka'
     'beam:schematransform:org.apache.beam:kafka_read:v1':
       name: 'ReadFromKafka'
+    'beam:schematransform:org.apache.beam:mqtt_write:v1':
+      name: 'WriteToMqtt'
+    'beam:schematransform:org.apache.beam:mqtt_read:v1':
+      name: 'ReadFromMqtt'
   skip_transforms:
     # Handwritten Kafka wrappers already exist in apache_beam/io/kafka.py
     - 'beam:schematransform:org.apache.beam:kafka_write:v1'

sdks/standard_external_transforms.yaml

@@ -19,7 +19,7 @@
 # configuration in /sdks/standard_expansion_services.yaml.
 # Refer to gen_xlang_wrappers.py for more info.
 #
-# Last updated on: 2026-05-06
+# Last updated on: 2026-06-10
 
 - default_service: sdks:java:io:expansion-service:shadowJar
   description: 'Outputs a PCollection of Beam Rows, each containing a single INT64
@@ -80,6 +80,61 @@
     type: str
   identifier: beam:schematransform:org.apache.beam:mongodb_write:v1
   name: MongodbWrite
+- default_service: sdks:java:io:expansion-service:shadowJar
+  description: 'Reads messages from an MQTT broker and outputs each payload as a single
+    `bytes` field.
+
+
+    By default the read is unbounded (streaming): it keeps consuming messages from
+    the subscribed topic until the pipeline is stopped. Setting `maxNumRecords` and/or
+    `maxReadTimeSeconds` bounds the read, producing a bounded (batch) PCollection.
+
+
+    Note: streaming reads require a runner that supports portable streaming (e.g.
+    Prism, Flink, or Dataflow). The legacy local Python DirectRunner does not execute
+    portable streaming cross-language reads.'
+  destinations:
+    python: apache_beam/io
+  fields:
+  - description: Configuration options to set up the MQTT connection.
+    name: connection_configuration
+    nullable: false
+    type: Row(client_id=typing.Optional[str], password=typing.Optional[str], server_uri=<class
+      'str'>, topic=typing.Optional[str], username=typing.Optional[str])
+  - description: The max number of records to receive. Setting this will result in
+      a bounded PCollection.
+    name: max_num_records
+    nullable: true
+    type: int64
+  - description: The maximum time for this source to read messages. Setting this will
+      result in a bounded PCollection.
+    name: max_read_time_seconds
+    nullable: true
+    type: int64
+  identifier: beam:schematransform:org.apache.beam:mqtt_read:v1
+  name: ReadFromMqtt
+- default_service: sdks:java:io:expansion-service:shadowJar
+  description: 'Publishes messages to an MQTT broker. Expects an input PCollection
+    of rows with a single `bytes` field, each of which is published as one MQTT message.
+
+
+    Works with both bounded (batch) and unbounded (streaming) input PCollections.'
+  destinations:
+    python: apache_beam/io
+  fields:
+  - description: Configuration options to set up the MQTT connection.
+    name: connection_configuration
+    nullable: false
+    type: Row(client_id=typing.Optional[str], password=typing.Optional[str], server_uri=<class
+      'str'>, topic=typing.Optional[str], username=typing.Optional[str])
+  - description: Whether or not the publish message should be retained by the messaging
+      engine. When a subscriber connects, it gets the latest retained message. Defaults
+      to `False`, which will clear the retained message from the server.
+    name: retained
+    nullable: true
+    type: boolean
+  identifier: beam:schematransform:org.apache.beam:mqtt_write:v1
+  name: WriteToMqtt
 - default_service: sdks:java:io:expansion-service:shadowJar
   description: ''
   destinations: