R1.5 GetTagExtendedPropertiesAsync (GetTepByNm) + R1.6 closed (no op)

Ship tag extended-property reads over the 2020 WCF aa/Retr/GetTepByNm op:
HistorianClient.GetTagExtendedPropertiesAsync(tag) -> name/value pairs.

String-handle op reached with the Open2 storage-session GUID formatted
uppercase (same format that unlocked GETRP/GETHI/ExeC). Routed via the
name-based native path (GetTagExtendedPropertiesByName, server-fetch flag),
not the index-based TagQuery path.

Evidence-backed findings from the capture:
- GetTepByNm (and GetTgByNm) succeed with the uppercase handle -- further
  validates the resolved string-handle wall.
- QTB (StartTagQuery) does NOT punch through: captured uppercase, it still
  fails server-side (CMdServer::StartActiveTagnamesQuery over the
  aahMetadataServer pipe) -- a metadata-server blocker, not handle format.
- R1.6 (localized properties) has NO distinct op (only error-message/UI-text
  localization in the managed client); collapses into R1.5. Closed, not throwing.

Wire format (golden-pinned, synthetic bytes -- no dev tag names committed):
- request tagNames = uint count + per-name(uint charCount + UTF-16)
- response = uint tagCount + per-tag(marker + compact-ASCII name +
  uint propCount + per-prop(marker + compact-ASCII name + 0x43 VT_BSTR value)
  + trailer); sequence-paged.

Adds: HistorianTagExtendedProperty model, HistorianTagExtendedPropertyProtocol
(codec), HistorianWcfTagExtendedPropertyClient (orchestration), dialect +
public API; golden WcfTagExtendedPropertyProtocolTests (4) + gated live test
(HISTORIAN_TEP_TAG). Tooling: Capture-TagExtendedProperties.ps1,
decode-tag-properties-capture.py, harness tag-extended-properties scenario.
Docs: wcf-tag-extended-properties.md; roadmap R1.5 DONE / R1.6 collapsed;
wall doc + memory updated with the QTB-server-side nuance. 228 tests green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01B6mcaT2PjRFKcogzp9UkfC

tests/AVEVA.Historian.Client.Tests/HistorianClientIntegrationTests.cs

@@ -296,6 +296,41 @@ public sealed class HistorianClientIntegrationTests
         Assert.False(string.IsNullOrWhiteSpace(value));
     }
 
+    [Fact]
+    public async Task GetTagExtendedPropertiesAsync_AgainstLocalHistorian_ReturnsProperties()
+    {
+        string? host = Environment.GetEnvironmentVariable("HISTORIAN_HOST");
+        // A tag that carries at least one extended property. Gated on its own env var so the test
+        // skips cleanly when no such tag is configured (no tag name is hardcoded).
+        string? tepTag = Environment.GetEnvironmentVariable("HISTORIAN_TEP_TAG");
+        if (string.IsNullOrWhiteSpace(host)
+            || !string.Equals(host, "localhost", StringComparison.OrdinalIgnoreCase)
+            || !OperatingSystem.IsWindows()
+            || string.IsNullOrWhiteSpace(tepTag))
+        {
+            return;
+        }
+
+        HistorianClient client = new(new HistorianClientOptions
+        {
+            Host = host,
+            IntegratedSecurity = true,
+            Transport = HistorianTransport.LocalPipe
+        });
+
+        // GetTepByNm rides the storage-session GUID as an uppercase string handle. The configured
+        // tag has at least one string-valued extended property (e.g. Location).
+        IReadOnlyList<AVEVA.Historian.Client.Models.HistorianTagExtendedProperty> properties =
+            await client.GetTagExtendedPropertiesAsync(tepTag, CancellationToken.None);
+
+        Assert.NotEmpty(properties);
+        Assert.All(properties, p =>
+        {
+            Assert.False(string.IsNullOrWhiteSpace(p.Name));
+            Assert.NotNull(p.Value);
+        });
+    }
+
     [Fact]
     public async Task GetConnectionStatusAsync_AgainstLocalHistorian_ReportsConnectedToServer()
     {