refactor(opcuaclient): move NamespaceMap to a .Session leaf so Contracts is dependency-light

G-7 wired OpcUaClientTagDefinitionFactory.Inspect into the deploy-time TagConfig
gate, which gave ControlPlane a ProjectReference to
Driver.OpcUaClient.Contracts — and with it, transitively, the whole OPC UA client
stack (5 OPCFoundation packages) into every host that loads the control plane.

NamespaceMap was the only reason Contracts carried
OPCFoundation.NetStandard.Opc.Ua.Client: its entire public surface is
ISession/NamespaceTable/NodeId-typed. It moves to a new leaf project,
ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Session, referenced by the runtime .Driver
and by .Browser. Contracts is left with Core.Abstractions and NOTHING else —
the same shape as Calculation.Contracts.

The namespace stays ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient, so no consumer's
`using` changed. The .Session -> .Contracts direction is deliberate: the blob
read NamespaceMap needs is OpcUaClientTagDefinitionFactory.TryReadNodeId, the
one authority it shares with the deploy gate, and that must stay in the
dependency-light half.

Why a new project rather than folding NamespaceMap into the runtime .Driver and
having .Browser reference it (the Driver.Mqtt.Browser #512-style deliberate
exception): the AdminUI project-references .Browser and NOT .Driver, so that
shape would pull the OpcUaClient driver runtime — plus Core,
Opc.Ua.Configuration and Secrets.Abstractions — into the AdminUI's build/deploy
graph. That is exactly the violation #512 spent two extractions removing from
Mqtt.Browser; re-introducing it to save one csproj is a bad trade.

Guard: ContractsIsDependencyLightTests (Driver.OpcUaClient.Tests) asserts the
Contracts manifest names no Opc.Ua* assembly, plus a counterpart asserting
.Session does. An ABSENCE assertion is sound on the manifest where a presence
one is not — the compiler elides an unused reference, but it MUST emit one the
moment Opc.Ua-typed code is added. Falsified by temporarily re-adding the
package plus an Opc.Ua.NodeId-typed member: red on Opc.Ua.Types, green again on
removal.

Evidence — `dotnet list ControlPlane package --include-transitive | grep -i opc`:
  before: OPCFoundation.NetStandard.Opc.Ua.{Client,Configuration,Core,
          Security.Certificates,Types} 1.5.378.106
  after:  none (and 0 Opc.Ua*.dll in ControlPlane's output directory)

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.Tests/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.Tests.csproj

@@ -22,7 +22,9 @@
 
     <ItemGroup>
         <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser\ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser.csproj"/>
-        <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Contracts\ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Contracts.csproj"/>
+        <!-- NamespaceMap.FromTable — it moved from .Contracts to the .Session leaf when .Contracts was
+             made dependency-light (ControlPlane references .Contracts for the G-7 deploy gate). -->
+        <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Session\ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Session.csproj"/>
         <ProjectReference Include="..\..\..\src\Core\ZB.MOM.WW.OtOpcUa.Commons\ZB.MOM.WW.OtOpcUa.Commons.csproj"/>
     </ItemGroup>
 

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests/ContractsIsDependencyLightTests.cs

@@ -0,0 +1,74 @@
+using Shouldly;
+using Xunit;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Tests;
+
+/// <summary>
+///     Pins the dependency shape of <c>ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Contracts</c>: it must not
+///     reference the OPC UA client SDK.
+///     <para>
+///         <b>Why this matters beyond tidiness.</b> Deferment-register G-7 wired
+///         <see cref="OpcUaClientTagDefinitionFactory.Inspect"/> into the deploy-time TagConfig gate, which
+///         made <c>ControlPlane</c> project-reference this Contracts assembly. ControlPlane is loaded by
+///         every admin- and driver-role host, so whatever Contracts drags in, they all carry. Contracts
+///         used to hold <c>NamespaceMap</c> — <c>ISession</c>/<c>NodeId</c>-typed throughout — and with it a
+///         <c>OPCFoundation.NetStandard.Opc.Ua.Client</c> PackageReference; NamespaceMap moved to the
+///         sibling <c>.Session</c> leaf so the parse-only half could stay light (the same shape as
+///         <c>Calculation.Contracts</c>: Core.Abstractions and nothing else).
+///     </para>
+///     <para>
+///         <b>Direction matters: this is an ABSENCE assertion, and that is what makes it sound here.</b>
+///         The assembly manifest is an unreliable witness for PRESENCE — the C# compiler elides a reference
+///         nothing in the IL actually uses, so "assembly X is referenced" can be false while the csproj says
+///         otherwise (the trap <c>EquipmentTagConfigInspectorCoverageTests</c> documents, which is why that
+///         one scans the output directory instead). Absence has no such hole in the direction that matters:
+///         the moment someone adds Opc.Ua-typed code to Contracts, the compiler MUST emit the reference and
+///         this test goes red. A csproj PackageReference that nothing consumes is elided and slips past —
+///         accepted deliberately, because an unused package reference is not the failure being guarded.
+///     </para>
+///     <para>
+///         Falsified 2026-08-09 by temporarily adding an <c>Opc.Ua.NodeId</c>-typed member to Contracts:
+///         the assertion failed naming <c>Opc.Ua.Core</c>, and passed again once removed.
+///     </para>
+/// </summary>
+public sealed class ContractsIsDependencyLightTests
+{
+    /// <summary>The Contracts assembly's manifest must name no OPC UA SDK assembly.</summary>
+    [Fact]
+    public void The_Contracts_assembly_does_not_reference_the_OPC_UA_SDK()
+    {
+        var contracts = typeof(OpcUaClientTagDefinitionFactory).Assembly;
+
+        // Positive control: name the assembly under test, so a rename/retarget cannot silently point this
+        // at something else that trivially satisfies the assertion below.
+        contracts.GetName().Name.ShouldBe("ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Contracts");
+
+        var opcUa = contracts.GetReferencedAssemblies()
+            .Select(a => a.Name ?? string.Empty)
+            .Where(n => n.StartsWith("Opc.Ua", StringComparison.OrdinalIgnoreCase))
+            .OrderBy(n => n, StringComparer.Ordinal)
+            .ToArray();
+
+        opcUa.ShouldBeEmpty(
+            "OpcUaClient.Contracts must stay free of the OPC UA client SDK — ControlPlane project-references "
+            + "it for the G-7 deploy-time TagConfig gate, so every host that loads the control plane would "
+            + "carry the stack. Put SDK-typed code in Driver.OpcUaClient.Session instead. Found: "
+            + string.Join(", ", opcUa));
+    }
+
+    /// <summary>
+    ///     The counterpart the assertion above is meaningful against: the SDK-typed half really did land
+    ///     somewhere, and that somewhere does reference the SDK. Without this, "no Opc.Ua reference
+    ///     anywhere" would read as a pass.
+    /// </summary>
+    [Fact]
+    public void The_Session_assembly_is_where_the_OPC_UA_SDK_reference_lives()
+    {
+        var session = typeof(NamespaceMap).Assembly;
+
+        session.GetName().Name.ShouldBe("ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Session");
+        session.GetReferencedAssemblies()
+            .Select(a => a.Name ?? string.Empty)
+            .ShouldContain(n => n.StartsWith("Opc.Ua", StringComparison.OrdinalIgnoreCase));
+    }
+}