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Array Write Ergonomics & Default-Fill Partial Writes — Implementation Plan

For Claude: REQUIRED SUB-SKILL: Use superpowers-extended-cc:executing-plans to implement this plan task-by-task.

Goal: Let clients write array attributes by their bare name (gateway auto-appends [] at AddItem), and write a sparse, default-filled array (only the indices they care about + a total length) instead of marshalling the whole array.

Architecture: All new behavior lives in the contract and the gateway; the worker is untouched and keeps doing an honest whole-array COM write. The gateway intercepts outbound commands at the single choke point GatewaySession.InvokeAsync(WorkerCommand): it (a) normalizes AddItem/AddItem2 item_definition to the [] form when Galaxy metadata says the attribute is an array, and (b) expands an MxSparseArray write value into a full default-filled MxArray before it leaves the gateway. Partial writes are stateless default-fill — unmentioned indices are the type default (reset), never preserved.

Tech Stack: .NET 10 (gateway) / .NET Framework 4.8 x86 (worker, unchanged), protobuf + Grpc.Tools, xUnit + FakeWorkerHarness; clients in C#, Go, Python, Rust, Java.

Design doc: docs/plans/2026-06-18-array-write-ergonomics-design.md

Key references for the implementer:

  • Choke point for all outbound commands: src/ZB.MOM.WW.MxGateway.Server/Sessions/GatewaySession.cs:947-955 (InvokeAsync(WorkerCommand command, ...)). command.Command is the MxCommand.
  • Handle→address tracking: GatewaySession.TrackCommandReply (lines 975-1014, AddItem at 989, AddItem2 at 992) → TrackItem (1826-1837) → SessionItemRegistration record (Sessions/SessionItemRegistration.cs). Tracking reads the same MxCommand instance that passed through InvokeAsync, so mutating item_definition there flows through automatically.
  • Galaxy metadata lookup: IGalaxyHierarchyCache.Current.Index.TagsByAddress.TryGetValue(addr, out GalaxyTagLookup), then lookup.Attribute?.IsArray. The index is keyed by FullTagReference, which already contains [] for arrays — look up addr + "[]". See Security/Authorization/ConstraintEnforcer.cs:15-17,197-204 for the injection + lookup pattern.
  • Proto: src/ZB.MOM.WW.MxGateway.Contracts/Protos/mxaccess_gateway.proto — MxValue (1026-1044), MxArray (1046-1063), WriteCommand (244-249), Write2Command (251-257), WriteSecuredCommand/WriteSecured2Command, WriteBulk*, AddItemCommand (192-195), AddItem2Command (197-201). Generated into Contracts/Generated/MxaccessGateway.cs (Compile-Removed + regenerated by Grpc.Tools).
  • Gateway proto regen + commit rule (memory project_proto_codegen_regen): after a .proto edit, delete Generated/*.cs, rebuild contracts to regenerate, and commit Generated/ or the net48 worker build fails CS0246.
  • Java client gotcha (memory project_java_generated_churn): gradle regenerates a tracked 64k-line file with spurious protobuf-version churn — revert that churn; build/test Java on windev (memory project_java_build_host), Mac has no JRE.

Task 0: Contract — add MxSparseArray and regenerate

Classification: high-risk Estimated implement time: ~4 min Parallelizable with: none (blocks all other tasks)

Files:

  • Modify: src/ZB.MOM.WW.MxGateway.Contracts/Protos/mxaccess_gateway.proto (MxValue oneof ~line 1043; new messages after MxArray ~line 1063)
  • Regenerate + commit: src/ZB.MOM.WW.MxGateway.Contracts/Generated/MxaccessGateway.cs

Step 1: Add the messages to the proto. After the MxArray message (line 1063), add:

// Write-only sparse array value. The gateway expands this into a full,
// default-filled MxArray before forwarding to the worker; the worker never
// receives or produces it. Unmentioned indices take the element type's
// default (reset, NOT preserved).
message MxSparseArray {
  MxDataType element_data_type = 1;
  uint32 total_length = 2;
  repeated MxSparseElement elements = 3;
}

message MxSparseElement {
  uint32 index = 1;
  MxValue value = 2; // scalar
}

Step 2: Add the oneof arm to MxValue. Inside the oneof kind { ... } block, after bytes raw_value = 18;:

    MxSparseArray sparse_array_value = 19;

Step 3: Regenerate generated code.

Run (PowerShell on windev, or locally on Mac — .NET builds fine):

del src/ZB.MOM.WW.MxGateway.Contracts/Generated/*.cs
dotnet build src/ZB.MOM.WW.MxGateway.Contracts/ZB.MOM.WW.MxGateway.Contracts.csproj

Expected: build succeeds; Generated/MxaccessGateway.cs now contains MxSparseArray, MxSparseElement, and MxValue.SparseArrayValue.

Step 4: Verify net10 + net48 both compile (the worker consumes these types via net48):

dotnet build src/ZB.MOM.WW.MxGateway.slnx

Expected: PASS (no CS0246 on the new types).

Step 5: Commit (include regenerated Generated/):

git add src/ZB.MOM.WW.MxGateway.Contracts/Protos/mxaccess_gateway.proto \
        src/ZB.MOM.WW.MxGateway.Contracts/Generated/MxaccessGateway.cs
git commit -m "feat(contracts): add MxSparseArray write-only value for default-fill partial writes"

Task 1: Gateway — SparseArrayExpander (pure expansion + validation)

Classification: standard Estimated implement time: ~5 min Parallelizable with: Task 2, Tasks 4-9

Files:

  • Create: src/ZB.MOM.WW.MxGateway.Server/Sessions/SparseArrayExpander.cs
  • Test: src/ZB.MOM.WW.MxGateway.Tests/Gateway/Sessions/SparseArrayExpanderTests.cs

Step 1: Write failing tests. Cover: default-fill sizing + placement (one per element type is enough for two types here, rest in step 4); total_length == 0 → InvalidArgument; index >= total_length → InvalidArgument; duplicate index → InvalidArgument; Raw/Unspecified element type → InvalidArgument; empty elements → all-defaults array of length N; timestamp default == Unix epoch.

using Grpc.Core;
using Mxaccess.Gateway.V1; // adjust to the generated namespace
using ZB.MOM.WW.MxGateway.Server.Sessions;
using Xunit;

public sealed class SparseArrayExpanderTests
{
    private static MxValue Sparse(MxDataType type, uint length, params (uint Index, MxValue Value)[] els)
    {
        MxSparseArray sparse = new() { ElementDataType = type, TotalLength = length };
        foreach ((uint index, MxValue value) in els)
            sparse.Elements.Add(new MxSparseElement { Index = index, Value = value });
        return new MxValue { SparseArrayValue = sparse };
    }

    [Fact]
    public void Expand_Int32_FillsDefaultsAndPlacesValues()
    {
        MxValue v = Sparse(MxDataType.Integer, 4, (1, new MxValue { Int32Value = 7 }));
        SparseArrayExpander.Expand(v);
        Assert.Equal(MxValue.KindOneofCase.ArrayValue, v.KindCase);
        Assert.Equal(new[] { 0, 7, 0, 0 }, v.ArrayValue.Int32Values.Values);
        Assert.Equal((uint)4, v.ArrayValue.Dimensions[0]);
    }

    [Fact]
    public void Expand_EmptyElements_ProducesAllDefaults()
    {
        MxValue v = Sparse(MxDataType.Boolean, 3);
        SparseArrayExpander.Expand(v);
        Assert.Equal(new[] { false, false, false }, v.ArrayValue.BoolValues.Values);
    }

    [Theory]
    [InlineData(0u, 0u)]   // total_length == 0
    [InlineData(2u, 5u)]   // index >= total_length
    public void Expand_InvalidShape_Throws(uint length, uint badIndex)
    {
        MxValue v = Sparse(MxDataType.Integer, length, (badIndex, new MxValue { Int32Value = 1 }));
        RpcException ex = Assert.Throws<RpcException>(() => SparseArrayExpander.Expand(v));
        Assert.Equal(StatusCode.InvalidArgument, ex.StatusCode);
    }

    [Fact]
    public void Expand_DuplicateIndex_Throws()
    {
        MxValue v = Sparse(MxDataType.Integer, 4,
            (1, new MxValue { Int32Value = 1 }), (1, new MxValue { Int32Value = 2 }));
        Assert.Throws<RpcException>(() => SparseArrayExpander.Expand(v));
    }
}

Step 2: Run, confirm fail. dotnet test src/ZB.MOM.WW.MxGateway.Tests/... --filter FullyQualifiedName~SparseArrayExpanderTests → FAIL (type not defined).

Step 3: Implement SparseArrayExpander. Mutates the passed MxValue in place, replacing SparseArrayValue with ArrayValue. Throw RpcException(new Status(StatusCode.InvalidArgument, msg)) on any validation failure. Element-type switch must cover the supported scalar element types (Boolean, Integer → int32 or int64, Float, Double, String, Time); default/timestamp default = Unix epoch (new Timestamp { Seconds = 0, Nanos = 0 }); reject Raw/Unknown/Unspecified. Set MxArray.Dimensions = { total_length } and ElementDataType. Validate: total_length > 0, every index < total_length, no duplicate indices, each element value scalar kind matches element_data_type.

(Mirror the typed sub-array shapes from VariantConverter.ConvertToComArray in the worker so the worker's existing read path is satisfied: Int32Values/Int64Values/BoolValues/FloatValues/DoubleValues/StringValues/TimestampValues with their Values repeated fields.)

Step 4: Add remaining element-type tests (int64, float, double, string, time/epoch, type-mismatch element → throws). Run filter → PASS.

Step 5: Commit.

git add src/ZB.MOM.WW.MxGateway.Server/Sessions/SparseArrayExpander.cs \
        src/ZB.MOM.WW.MxGateway.Tests/Gateway/Sessions/SparseArrayExpanderTests.cs
git commit -m "feat(gateway): add SparseArrayExpander for default-fill partial array writes"

Task 2: Gateway — ArrayAddressNormalizer (suffix normalization)

Classification: standard Estimated implement time: ~5 min Parallelizable with: Task 1, Tasks 4-9

Files:

  • Create: src/ZB.MOM.WW.MxGateway.Server/Sessions/ArrayAddressNormalizer.cs
  • Test: src/ZB.MOM.WW.MxGateway.Tests/Gateway/Sessions/ArrayAddressNormalizerTests.cs

Step 1: Write failing tests using a fake/in-memory IGalaxyHierarchyCache whose Current.Index.TagsByAddress contains "Obj.Arr[]" (array) and "Obj.Scalar" (non-array). Cases:

  • "Obj.Arr" (bare, is array) → "Obj.Arr[]".
  • "Obj.Arr[]" (already suffixed) → unchanged.
  • "Obj.Scalar" (non-array) → unchanged.
  • "Obj.Unknown" (not in cache / metadata cold) → unchanged (pass-through fallback).
[Fact]
public void Normalize_BareArrayName_AppendsSuffix()
{
    ArrayAddressNormalizer normalizer = new(FakeCacheWith("Obj.Arr[]", isArray: true));
    Assert.Equal("Obj.Arr[]", normalizer.Normalize("Obj.Arr"));
}

[Theory]
[InlineData("Obj.Arr[]")]   // already suffixed
[InlineData("Obj.Scalar")]  // non-array
[InlineData("Obj.Unknown")] // not in cache → fallback pass-through
public void Normalize_LeavesUnchanged(string address) =>
    Assert.Equal(address, new ArrayAddressNormalizer(FakeCacheWith("Obj.Arr[]", true)).Normalize(address));

Step 2: Run, confirm fail.

Step 3: Implement. Constructor injects IGalaxyHierarchyCache cache. Normalize(string):

  1. If string.IsNullOrWhiteSpace(address) or address.EndsWith("[]", StringComparison.Ordinal) → return unchanged.
  2. Look up address + "[]" in cache.Current.Index.TagsByAddress. If found and lookup.Attribute?.IsArray == true → return address + "[]".
  3. Otherwise return address unchanged. Never throw (best-effort convenience).

Step 4: Run filter → PASS.

Step 5: Commit.

git add src/ZB.MOM.WW.MxGateway.Server/Sessions/ArrayAddressNormalizer.cs \
        src/ZB.MOM.WW.MxGateway.Tests/Gateway/Sessions/ArrayAddressNormalizerTests.cs
git commit -m "feat(gateway): add ArrayAddressNormalizer for bare-name array AddItem"

Task 3: Gateway — wire normalization + expansion into the outbound path

Classification: high-risk Estimated implement time: ~5 min Parallelizable with: none (depends on Tasks 1, 2)

Files:

  • Modify: src/ZB.MOM.WW.MxGateway.Server/Sessions/GatewaySession.cs (constructor — inject ArrayAddressNormalizer; InvokeAsync at 947-955)
  • Modify: DI registration wherever ArrayAddressNormalizer/GatewaySession deps are registered (search Security/Authorization/ConstraintEnforcer registration for the pattern; register ArrayAddressNormalizer as scoped/singleton consistent with IGalaxyHierarchyCache)
  • Test: src/ZB.MOM.WW.MxGateway.Tests/Gateway/Sessions/GatewayArrayWriteWiringTests.cs

Step 1: Write a failing integration test with FakeWorkerHarness (pattern: src/ZB.MOM.WW.MxGateway.Tests/Gateway/Workers/FakeWorkerHarnessTests.cs:51-69 — CreateConnectedPairAsync, ReadCommandAsync, ReplyToCommandAsync). Two assertions:

  1. Client sends AddItemCommand{ item_definition = "Obj.Arr" } (array per the test's Galaxy cache) → the WorkerEnvelope the fake worker reads has item_definition == "Obj.Arr[]".
  2. Client sends WriteCommand{ value = MxSparseArray(Integer, 4, {1:7}) } → the worker receives value.ArrayValue.Int32Values.Values == [0,7,0,0] (no SparseArrayValue reaches the worker).

Step 2: Run, confirm fail.

Step 3: Implement. At the top of InvokeAsync(WorkerCommand command, ...), before forwarding, transform command.Command (the MxCommand) by PayloadCase:

  • AddItem → command.Command.AddItem.ItemDefinition = _addressNormalizer.Normalize(command.Command.AddItem.ItemDefinition);
  • AddItem2 → same on AddItem2.ItemDefinition.
  • Write/WriteSecured → if cmd.Value?.KindCase == SparseArrayValue call SparseArrayExpander.Expand(cmd.Value).
  • Write2/WriteSecured2 → expand Value only (not TimestampValue).
  • WriteBulk/Write2Bulk/WriteSecuredBulk/WriteSecured2Bulk → expand each entry.Value.

Keep it a single private helper NormalizeOutbound(MxCommand) called once at the choke point. Because TrackCommandReply later reads the same MxCommand instance, the normalized item_definition flows into SessionItemRegistration with no extra change — add an assertion in the test that TryGetItemRegistration(...).TagAddress == "Obj.Arr[]" to lock that in.

Step 4: Run the wiring test + Tasks 1/2 filters → PASS. Then run the AddItem/Write fake-worker regression group once:

dotnet test src/ZB.MOM.WW.MxGateway.Tests/ZB.MOM.WW.MxGateway.Tests.csproj --filter "FullyQualifiedName~ArrayWrite|FullyQualifiedName~SparseArray|FullyQualifiedName~ArrayAddressNormalizer"

Step 5: Commit.

git add src/ZB.MOM.WW.MxGateway.Server/Sessions/GatewaySession.cs \
        src/ZB.MOM.WW.MxGateway.Tests/Gateway/Sessions/GatewayArrayWriteWiringTests.cs
git commit -m "feat(gateway): normalize array AddItem suffix and expand sparse writes at the worker boundary"

Tasks 4-8: Client helpers + READMEs (one task per client, parallelizable)

Each client task does the same four things; only paths/idioms differ. Depends on Task 0 (needs regenerated proto types). All five are parallelizable with each other and with Tasks 1-3, 9.

Common helper contract: WriteArrayElements(serverHandle, itemHandle, elementDataType, totalLength, elements /* index→scalar MxValue */, userId) builds an MxValue { SparseArrayValue = MxSparseArray{...} } and calls the existing raw write. Add a unit test that the built command carries sparse_array_value with the right total_length/indices (serialization round-trip; no live gateway). Update the "Array writes replace the whole array" README section to document: default-fill semantics (unmentioned = reset to default, not preserved), the required total_length, and that bare-name array writes now auto-normalize.

Task 4: .NET client

Classification: standard · ~4 min · Parallelizable with: Tasks 5-9, 1-3

  • Regenerate types: dotnet build clients/dotnet/ZB.MOM.WW.MxGateway.Client.slnx.
  • Add helper next to WriteAsync in clients/dotnet/ZB.MOM.WW.MxGateway.Client/MxGatewaySession.cs:678-688.
  • Test alongside existing client tests; README clients/dotnet/README.md:162-170.
  • Verify: build slnx + dotnet test the client test project.

Task 5: Go client

Classification: standard · ~4 min · Parallelizable with: Tasks 4,6-9, 1-3

  • Regenerate per clients/go README; helper next to Write/WriteRaw in clients/go/mxgateway/session.go:559-581.
  • README clients/go/README.md:139-147.
  • Verify: gofmt, go build ./..., go test ./... from clients/go.

Task 6: Python client

Classification: standard · ~4 min · Parallelizable with: Tasks 4-5,7-9, 1-3

  • Regenerate per clients/python README; helper next to write in clients/python/src/zb_mom_ww_mxgateway/session.py:469-490.
  • README clients/python/README.md:142-150.
  • Verify: python -m pytest from clients/python.

Task 7: Rust client

Classification: standard · ~4 min · Parallelizable with: Tasks 4-6,8-9, 1-3

  • Helper next to write in clients/rust/src/session.rs:530-548; conversion helpers in clients/rust/src/value.rs.
  • README clients/rust/README.md:162-170.
  • Verify: cargo fmt, cargo check --workspace, cargo test --workspace, cargo clippy --all-targets -- -D warnings from clients/rust.

Task 8: Java client

Classification: standard · ~5 min · Parallelizable with: Tasks 4-7,9, 1-3

  • Helper next to write/writeRaw in clients/java/.../client/MxGatewaySession.java:581-604.
  • README clients/java/README.md:118-126.
  • Build/test on windev (JDK 21) via an isolated origin/<branch> worktree — Mac has no JRE (memory project_java_build_host). After gradle regen, revert the spurious protobuf-version churn in clients/java/src/main/generated/.../MxaccessGateway.java if no proto semantics beyond the new messages changed (memory project_java_generated_churn); keep only the real MxSparseArray additions.
  • Verify: gradle test on windev.

(Each client task ends with its own commit, e.g. feat(client-<lang>): add WriteArrayElements default-fill helper and document semantics.)

Task 9: Docs — gateway.md + value conversion

Classification: small Estimated implement time: ~3 min Parallelizable with: Tasks 1-8 (depends on Task 0 only)

Files:

  • Modify: gateway.md (command/value surface — document MxSparseArray as a write-only value and bare-name AddItem normalization)
  • Modify: the value-conversion doc under docs/ (search for where MxArray/value conversion is described) — add the default-fill + epoch-default note and the parity statement (worker still does a whole-array COM write)

Step 1: Add a subsection describing: sparse_array_value is write-only and gateway-expanded; default-fill semantics (epoch for time); total_length required; bare-name array writes auto-normalize to [] at AddItem with metadata pass-through fallback; non-goal: no preserve-unchanged merge, no element-wise COM write.

Step 2: Commit.

git add gateway.md docs/
git commit -m "docs: document MxSparseArray default-fill writes and bare-name array AddItem"

Dependency summary

  • Task 0 blocks everything.
  • Tasks 1, 2 depend on 0; parallel with each other.
  • Task 3 depends on 1 and 2.
  • Tasks 4-8 depend on 0; parallel with each other and with 1-3, 9.
  • Task 9 depends on 0; parallel with all.

Verification gates (per CLAUDE.md targeted-tests rule)

  • Run only the --filter for the task you touched; run the array-write fake-worker group once after Task 3.
  • Java verified on windev only. .NET/Go/Rust/Python verified locally.
  • Live MXAccess (opt-in, windev): after merge, one default-fill write and one bare-name array write against real COM (MXGATEWAY_RUN_LIVE_MXACCESS_TESTS=1).
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