feat(client-python): add write_array_elements default-fill helper and document semantics

Regenerate Python proto bindings to pick up MxSparseArray/MxSparseElement/
sparse_array_value from the shared mxaccess_gateway.proto. Add
Session.write_array_elements which builds an MxValue(sparse_array_value=…)
from a {index→scalar} dict and delegates to the existing write(). Add 8 pytest
tests covering builder correctness and full round-trip wire shape. Update
README with a default-fill semantics paragraph and bare-name array-write note.

clients/python/README.md

@@ -148,6 +148,33 @@ the unchanged elements included. For example, to change 2 elements of a
 the 2 new ones). Sending only the 2 changed values overwrites the attribute
 with a 2-element array.
 
+### Default-fill partial array writes
+
+`Session.write_array_elements` lets you write only the indices you care about.
+The gateway fills every unmentioned position with the type default for the
+declared `element_data_type` (0, `False`, `""`, Unix epoch for timestamps).
+The previous value at those positions is **not** preserved — the gateway expands
+the sparse map to a full array before forwarding the write to MXAccess, so this
+is still a full replacement:
+
+```python
+# Write indices 0 and 5 of a 10-element integer array.
+# Positions 1-4 and 6-9 become 0, not their previous values.
+await session.write_array_elements(
+    server_handle=server_handle,
+    item_handle=item_handle,
+    element_data_type=pb.MX_DATA_TYPE_INTEGER,
+    total_length=10,
+    elements={0: 100, 5: 500},
+)
+```
+
+Bare-name array items (e.g. `Object.ArrayAttr` without an index suffix) added
+via `add_item` auto-normalize to `[]` — they refer to the whole array, not a
+single element. Writes through such handles must cover the full array or use
+`write_array_elements` to supply `total_length` and let the gateway fill
+defaults for the rest.
+
 ## Galaxy Repository Browse
 
 The `GalaxyRepositoryClient` wraps the read-only `GalaxyRepository` gRPC

clients/python/src/zb_mom_ww_mxgateway/generated/galaxy_repository_pb2.py

@@ -2,7 +2,7 @@
 # Generated by the protocol buffer compiler.  DO NOT EDIT!
 # NO CHECKED-IN PROTOBUF GENCODE
 # source: galaxy_repository.proto
-# Protobuf Python Version: 6.31.1
+# Protobuf Python Version: 6.33.5
 """Generated protocol buffer code."""
 from google.protobuf import descriptor as _descriptor
 from google.protobuf import descriptor_pool as _descriptor_pool
@@ -12,8 +12,8 @@ from google.protobuf.internal import builder as _builder
 _runtime_version.ValidateProtobufRuntimeVersion(
     _runtime_version.Domain.PUBLIC,
     6,
-    31,
+    33,
-    1,
+    5,
     '',
     'galaxy_repository.proto'
 )

clients/python/src/zb_mom_ww_mxgateway/generated/galaxy_repository_pb2_grpc.py

@@ -5,7 +5,7 @@ import warnings
 
 import galaxy_repository_pb2 as galaxy__repository__pb2
 
-GRPC_GENERATED_VERSION = '1.80.0'
+GRPC_GENERATED_VERSION = '1.81.1'
 GRPC_VERSION = grpc.__version__
 _version_not_supported = False
 
@@ -25,7 +25,7 @@ if _version_not_supported:
     )
 
 
-class GalaxyRepositoryStub(object):
+class GalaxyRepositoryStub:
     """Wire-compatibility policy (ProtobufStyleGuide): this contract evolves
     additively only. Never renumber or repurpose an existing field number or
     enum value. When a field or enum value is removed, add a `reserved` range
@@ -72,7 +72,7 @@ class GalaxyRepositoryStub(object):
                 _registered_method=True)
 
 
-class GalaxyRepositoryServicer(object):
+class GalaxyRepositoryServicer:
     """Wire-compatibility policy (ProtobufStyleGuide): this contract evolves
     additively only. Never renumber or repurpose an existing field number or
     enum value. When a field or enum value is removed, add a `reserved` range
@@ -162,7 +162,7 @@ def add_GalaxyRepositoryServicer_to_server(servicer, server):
 
 
  # This class is part of an EXPERIMENTAL API.
-class GalaxyRepository(object):
+class GalaxyRepository:
     """Wire-compatibility policy (ProtobufStyleGuide): this contract evolves
     additively only. Never renumber or repurpose an existing field number or
     enum value. When a field or enum value is removed, add a `reserved` range

clients/python/src/zb_mom_ww_mxgateway/generated/mxaccess_gateway_pb2_grpc.py

@@ -5,7 +5,7 @@ import warnings
 
 import mxaccess_gateway_pb2 as mxaccess__gateway__pb2
 
-GRPC_GENERATED_VERSION = '1.80.0'
+GRPC_GENERATED_VERSION = '1.81.1'
 GRPC_VERSION = grpc.__version__
 _version_not_supported = False
 
@@ -25,7 +25,7 @@ if _version_not_supported:
     )
 
 
-class MxAccessGatewayStub(object):
+class MxAccessGatewayStub:
     """Wire-compatibility policy (ProtobufStyleGuide): this contract evolves
     additively only. Never renumber or repurpose an existing field number or
     enum value. When a field or enum value is removed, add a `reserved` range
@@ -78,7 +78,7 @@ class MxAccessGatewayStub(object):
                 _registered_method=True)
 
 
-class MxAccessGatewayServicer(object):
+class MxAccessGatewayServicer:
     """Wire-compatibility policy (ProtobufStyleGuide): this contract evolves
     additively only. Never renumber or repurpose an existing field number or
     enum value. When a field or enum value is removed, add a `reserved` range
@@ -189,7 +189,7 @@ def add_MxAccessGatewayServicer_to_server(servicer, server):
 
 
  # This class is part of an EXPERIMENTAL API.
-class MxAccessGateway(object):
+class MxAccessGateway:
     """Wire-compatibility policy (ProtobufStyleGuide): this contract evolves
     additively only. Never renumber or repurpose an existing field number or
     enum value. When a field or enum value is removed, add a `reserved` range

clients/python/src/zb_mom_ww_mxgateway/generated/mxaccess_worker_pb2.py

@@ -2,7 +2,7 @@
 # Generated by the protocol buffer compiler.  DO NOT EDIT!
 # NO CHECKED-IN PROTOBUF GENCODE
 # source: mxaccess_worker.proto
-# Protobuf Python Version: 6.31.1
+# Protobuf Python Version: 6.33.5
 """Generated protocol buffer code."""
 from google.protobuf import descriptor as _descriptor
 from google.protobuf import descriptor_pool as _descriptor_pool
@@ -12,8 +12,8 @@ from google.protobuf.internal import builder as _builder
 _runtime_version.ValidateProtobufRuntimeVersion(
     _runtime_version.Domain.PUBLIC,
     6,
-    31,
+    33,
-    1,
+    5,
     '',
     'mxaccess_worker.proto'
 )

clients/python/src/zb_mom_ww_mxgateway/generated/mxaccess_worker_pb2_grpc.py

@@ -4,7 +4,7 @@ import grpc
 import warnings
 
 
-GRPC_GENERATED_VERSION = '1.80.0'
+GRPC_GENERATED_VERSION = '1.81.1'
 GRPC_VERSION = grpc.__version__
 _version_not_supported = False
 

clients/python/src/zb_mom_ww_mxgateway/session.py

@@ -489,6 +489,56 @@ class Session:
             correlation_id=correlation_id,
         )
 
+    async def write_array_elements(
+        self,
+        server_handle: int,
+        item_handle: int,
+        element_data_type: "pb.MxDataType.ValueType",
+        total_length: int,
+        elements: dict[int, MxValueInput],
+        *,
+        user_id: int = 0,
+        correlation_id: str = "",
+    ) -> None:
+        """Write a partial array by specifying only the indices you want to set.
+
+        The gateway expands the sparse representation into a full ``total_length``
+        array before forwarding the write to MXAccess.  Indices not listed in
+        *elements* are filled with the type default for *element_data_type* (0,
+        False, empty string, Unix epoch for timestamps, etc.).  The previous
+        value at those positions is **not** preserved — this is a full array
+        replacement, not a patch.
+
+        Args:
+            server_handle: Handle returned by :meth:`register`.
+            item_handle: Handle returned by :meth:`add_item`.
+            element_data_type: ``pb.MX_DATA_TYPE_*`` enum value for the scalar
+                element type of the target array attribute.
+            total_length: Total number of elements in the written array.  Must
+                be > 0 and large enough to contain every index in *elements*.
+            elements: Mapping of zero-based element index to scalar value.
+                Values are converted with :func:`~zb_mom_ww_mxgateway.values.to_mx_value`.
+            user_id: Galaxy user id to stamp on the write (requires a prior
+                supervisory advise to take effect — see README).
+            correlation_id: Optional client-supplied correlation token echoed
+                in the command reply.
+        """
+        sparse = pb.MxSparseArray(
+            element_data_type=element_data_type,
+            total_length=total_length,
+            elements=[
+                pb.MxSparseElement(index=idx, value=to_mx_value(val))
+                for idx, val in elements.items()
+            ],
+        )
+        await self.write(
+            server_handle,
+            item_handle,
+            pb.MxValue(sparse_array_value=sparse),
+            user_id=user_id,
+            correlation_id=correlation_id,
+        )
+
     async def write2(
         self,
         server_handle: int,

clients/python/tests/test_write_array_elements.py

@@ -0,0 +1,209 @@
+"""Tests for Session.write_array_elements default-fill sparse-array helper."""
+
+from __future__ import annotations
+
+from typing import Any
+
+import pytest
+
+from zb_mom_ww_mxgateway import ClientOptions, GatewayClient
+from zb_mom_ww_mxgateway.generated import mxaccess_gateway_pb2 as pb
+
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+
+def _make_sparse_mx_value(
+    element_data_type: "pb.MxDataType.ValueType",
+    total_length: int,
+    elements: dict[int, Any],
+) -> pb.MxValue:
+    """Build an MxValue wrapping an MxSparseArray from Python primitives.
+
+    Mirrors the logic inside Session.write_array_elements so tests can assert
+    the exact wire shape the helper produces without going through the full
+    gRPC stack.
+    """
+    from zb_mom_ww_mxgateway.values import to_mx_value
+
+    return pb.MxValue(
+        sparse_array_value=pb.MxSparseArray(
+            element_data_type=element_data_type,
+            total_length=total_length,
+            elements=[
+                pb.MxSparseElement(index=idx, value=to_mx_value(val))
+                for idx, val in elements.items()
+            ],
+        )
+    )
+
+
+# ---------------------------------------------------------------------------
+# Fake stub (minimal — only needs Invoke / OpenSession)
+# ---------------------------------------------------------------------------
+
+
+class _FakeUnary:
+    def __init__(self, replies: list[Any]) -> None:
+        self.replies = list(replies)
+        self.requests: list[Any] = []
+        self.metadata: tuple[tuple[str, str], ...] | None = None
+
+    async def __call__(
+        self,
+        request: Any,
+        *,
+        metadata: tuple[tuple[str, str], ...],
+    ) -> Any:
+        self.requests.append(request)
+        self.metadata = metadata
+        return self.replies.pop(0)
+
+
+class _FakeStub:
+    """Minimal stub that satisfies GatewayClient for a single invoke round-trip."""
+
+    def __init__(self) -> None:
+        ok = pb.ProtocolStatus(code=pb.PROTOCOL_STATUS_CODE_OK)
+        self.open_session = _FakeUnary([pb.OpenSessionReply(session_id="s1", protocol_status=ok)])
+        self.invoke = _FakeUnary(
+            [
+                pb.MxCommandReply(
+                    session_id="s1",
+                    kind=pb.MX_COMMAND_KIND_WRITE,
+                    protocol_status=ok,
+                ),
+            ]
+        )
+        self.OpenSession = self.open_session
+        self.Invoke = self.invoke
+
+
+# ---------------------------------------------------------------------------
+# Unit tests
+# ---------------------------------------------------------------------------
+
+
+def test_sparse_mx_value_builder_sets_correct_oneof() -> None:
+    """Builder helper must produce an MxValue with kind == 'sparse_array_value'."""
+    mv = _make_sparse_mx_value(pb.MX_DATA_TYPE_INTEGER, 5, {0: 10, 3: 30})
+    assert mv.WhichOneof("kind") == "sparse_array_value"
+
+
+def test_sparse_mx_value_builder_total_length() -> None:
+    """total_length must equal the value passed to the builder."""
+    mv = _make_sparse_mx_value(pb.MX_DATA_TYPE_INTEGER, 20, {1: 7})
+    assert mv.sparse_array_value.total_length == 20
+
+
+def test_sparse_mx_value_builder_element_count_and_values() -> None:
+    """Elements list length and scalar values must match the input dict."""
+    mv = _make_sparse_mx_value(pb.MX_DATA_TYPE_INTEGER, 10, {0: 11, 4: 55, 9: 99})
+    sa = mv.sparse_array_value
+    assert len(sa.elements) == 3
+    by_index = {e.index: e.value for e in sa.elements}
+    assert by_index[0].int32_value == 11
+    assert by_index[4].int32_value == 55
+    assert by_index[9].int32_value == 99
+
+
+def test_sparse_mx_value_builder_element_data_type() -> None:
+    """element_data_type must be forwarded verbatim."""
+    mv = _make_sparse_mx_value(pb.MX_DATA_TYPE_FLOAT, 3, {})
+    assert mv.sparse_array_value.element_data_type == pb.MX_DATA_TYPE_FLOAT
+
+
+def test_sparse_mx_value_builder_empty_elements() -> None:
+    """An empty elements dict must still produce a valid MxSparseArray."""
+    mv = _make_sparse_mx_value(pb.MX_DATA_TYPE_BOOLEAN, 8, {})
+    sa = mv.sparse_array_value
+    assert len(sa.elements) == 0
+    assert sa.total_length == 8
+
+
+# ---------------------------------------------------------------------------
+# Integration-level: write_array_elements routes through Session.write
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_write_array_elements_sends_sparse_array_write_command() -> None:
+    """write_array_elements must send a WRITE command whose value is sparse_array_value."""
+    stub = _FakeStub()
+    client = await GatewayClient.connect(
+        ClientOptions(endpoint="fake", api_key="mxgw_test_secret", plaintext=True),
+        stub=stub,
+    )
+    session = await client.open_session()
+
+    await session.write_array_elements(
+        server_handle=1,
+        item_handle=2,
+        element_data_type=pb.MX_DATA_TYPE_INTEGER,
+        total_length=10,
+        elements={0: 100, 5: 500},
+    )
+
+    assert len(stub.invoke.requests) == 1
+    cmd_req: pb.MxCommandRequest = stub.invoke.requests[0]
+    cmd = cmd_req.command
+    assert cmd.kind == pb.MX_COMMAND_KIND_WRITE
+    mv = cmd.write.value
+    assert mv.WhichOneof("kind") == "sparse_array_value"
+
+    sa = mv.sparse_array_value
+    assert sa.element_data_type == pb.MX_DATA_TYPE_INTEGER
+    assert sa.total_length == 10
+    assert len(sa.elements) == 2
+    by_index = {e.index: e.value for e in sa.elements}
+    assert by_index[0].int32_value == 100
+    assert by_index[5].int32_value == 500
+
+
+@pytest.mark.asyncio
+async def test_write_array_elements_forwards_user_id() -> None:
+    """user_id must reach the WriteCommand."""
+    stub = _FakeStub()
+    client = await GatewayClient.connect(
+        ClientOptions(endpoint="fake", api_key="mxgw_test_secret", plaintext=True),
+        stub=stub,
+    )
+    session = await client.open_session()
+
+    await session.write_array_elements(
+        server_handle=1,
+        item_handle=2,
+        element_data_type=pb.MX_DATA_TYPE_BOOLEAN,
+        total_length=4,
+        elements={},
+        user_id=42,
+    )
+
+    cmd = stub.invoke.requests[0].command
+    assert cmd.write.user_id == 42
+
+
+@pytest.mark.asyncio
+async def test_write_array_elements_string_elements() -> None:
+    """String element values must be encoded as string_value scalars."""
+    stub = _FakeStub()
+    client = await GatewayClient.connect(
+        ClientOptions(endpoint="fake", api_key="mxgw_test_secret", plaintext=True),
+        stub=stub,
+    )
+    session = await client.open_session()
+
+    await session.write_array_elements(
+        server_handle=1,
+        item_handle=2,
+        element_data_type=pb.MX_DATA_TYPE_STRING,
+        total_length=3,
+        elements={1: "hello", 2: "world"},
+    )
+
+    sa = stub.invoke.requests[0].command.write.value.sparse_array_value
+    by_index = {e.index: e.value for e in sa.elements}
+    assert by_index[1].string_value == "hello"
+    assert by_index[2].string_value == "world"