fix(gateway): resolve 2026-06-18 array-write review findings

- Server-057: extend []-suffix normalization to AddItemBulk/AddBufferedItem so bulk-added
  array tags bind write-capable handles (authz check, worker bind, and registration kept
  consistent); update gateway.md + client READMEs. Tests: AddItemBulk/AddBufferedItem wiring.
- Server-058: assert []-fallback-resolved bare array names are still denied when out of
  read/write scope and that MaxWriteClassification is enforced on suffixed array registrations.
- Contracts-023/024/025: round-trip + field-19 descriptor pin for MxSparseArray; document
  MxSparseArray in docs/Contracts.md; enumerate it in the protocol-version-3 test summary.
- Tests-040: add wiring tests for the six uncovered sparse-write arms (WriteSecured, Write2,
  WriteSecured2, Write2Bulk, WriteSecuredBulk, WriteSecured2Bulk).

dotnet build + targeted tests green (184 passed).

code-reviews/Tests/findings.md

@@ -7,7 +7,7 @@
 | Review date | 2026-06-18 |
 | Commit reviewed | `88915c3` |
 | Status | Re-reviewed |
-| Open findings | 1 |
+| Open findings | 0 |
 
 ## Checklist coverage
 
@@ -749,8 +749,10 @@ The cancellation tests for `WorkerClient` in `WorkerClientTests` *do* exercise t
 | Severity | Low |
 | Category | Testing coverage |
 | Location | `src/ZB.MOM.WW.MxGateway.Tests/Gateway/Sessions/GatewayArrayWriteWiringTests.cs` |
-| Status | Open |
+| Status | Resolved |
 
 **Description:** `GatewayArrayWriteWiringTests` covers two of eight sparse-write arms in `GatewaySession.NormalizeOutboundCommand`: `Write` (single) and `WriteBulk`. The remaining six arms — `WriteSecured`, `Write2`, `WriteSecured2`, `Write2Bulk`, `WriteSecuredBulk`, `WriteSecured2Bulk` — all call `ExpandValue(entry.Value)` through the same switch, but no wiring test exercises them through `GatewaySession.InvokeAsync`. The class summary says it covers "the single outbound choke point" and that "no sparse value is ever forwarded"; the claim is accurate for the two covered variants but unverified for the other six. A regression accidentally dropping one of the six remaining `case` arms, or shifting a brace so a case falls through to the default (no-op), would pass the entire `GatewayArrayWriteWiringTests` suite.
 
 **Recommendation:** Add one wiring test per uncovered variant (or a single `[Theory]` over the six command kinds), constructing the matching command type with a `SparseArrayValue` and asserting `worker.LastCommand!.Command.<Variant>.Value.KindCase == MxValue.KindOneofCase.ArrayValue` after `session.InvokeAsync`. The `SparseArrayExpanderTests` already pin the expander logic exhaustively; the wiring tests need only check that the choke point invokes expansion for each variant, not the expansion semantics themselves. The four secured variants (`WriteSecured`, `Write2`, `WriteSecured2`, `WriteSecured2Bulk`) can reuse the same `CapturingWorkerClient` stub.
+
+**Resolution:** 2026-06-18 — root cause confirmed: the six arms (`WriteSecured`, `Write2`, `WriteSecured2`, `Write2Bulk`, `WriteSecuredBulk`, `WriteSecured2Bulk`) each had a `case` in `NormalizeOutboundCommand` calling `ExpandValue` but no wiring test. Server-057's additions (`AddItemBulk`, `AddBufferedItem`) covered address-normalization tests only, not the missing write-expansion variants. Added six tests to `GatewayArrayWriteWiringTests.cs` — one per uncovered arm — each constructing the matching command with a 4-element `SparseArrayValue` (Integer, single element set), driving it through `GatewaySession.InvokeAsync`, and asserting `worker.LastCommand.Command.<Variant>.Value.KindCase == ArrayValue` and the expected element positions. Tests: `WriteSecured_SparseArrayValue_ExpandedBeforeReachingWorker`, `Write2_SparseArrayValue_ExpandedBeforeReachingWorker`, `WriteSecured2_SparseArrayValue_ExpandedBeforeReachingWorker`, `Write2Bulk_SparseArrayEntryValue_ExpandedBeforeReachingWorker`, `WriteSecuredBulk_SparseArrayEntryValue_ExpandedBeforeReachingWorker`, `WriteSecured2Bulk_SparseArrayEntryValue_ExpandedBeforeReachingWorker`. All 13 `GatewayArrayWriteWiring` tests pass (7 pre-existing + 6 new).