M2: implement SendEventAsync — event-send rides WCF AddS2, not the storage pipe

Roadmap Milestone 2 (event sending). Capture disproved the assumption that event
delivery uses the non-WCF storage-engine pipe (which would block it like revision
writes): a native AddStreamedValue(HistorianEvent) leaves over WCF as AddS2
(IHistoryServiceContract2.AddStreamValues2). CM_EVENT is a built-in registered tag,
so the 129 TagNotFoundInCache gate that blocks AddS2 for user tags does not apply.

- R2.1: NativeTraceHarness "event-send" scenario + Capture-EventSend.ps1; two
  captures diffed to separate constant framing from value-dependent fields.
- R2.2: HistorianEventWriteProtocol serializes the AddS2 pBuf (storage sample buffer
  wrapping the event VTQ) — golden-byte tested. Decoded "OS" sig + length fields +
  CM_EVENT tag id + EventTime/ReceivedTime FILETIMEs + Opc 192 + 0x118D descriptor +
  event Id + Namespace + EventType + version 5 + typed property bag.
- R2.3/R2.4: HistorianWcfEventOrchestrator.SendEventAsync (Open2 event-mode 0x501 ->
  reuse CM_EVENT RTag2/EnsT2 -> AddStreamValues2) + HistorianClient.SendEventAsync.
- R2.5: gated live test; server accepts the AddS2 (success, empty error buffer).

Server requires delivered byte[].Length == declared packet length (uint32@0x04); the
native relies on the MDAS encoder adding a pad byte, so the SDK emits an explicit
trailing 0x00 (else AddS2 rejects with "CValuStream buffer size vs packet length
mismatch"). Original events only (RevisionVersion=0) with string properties; other
property types + revision/update/delete throw ProtocolEvidenceMissingException.

Caveat (documented): accepted events are not persisted on the local dev box; the
native client behaves identically (event ingestion pipeline inactive) — not an SDK
gap. 212 unit tests pass; 16/16 event tests pass live.

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

src/AVEVA.Historian.Client/HistorianClient.cs

@@ -93,6 +93,21 @@ public sealed class HistorianClient : IAsyncDisposable
         return _protocol.ReadEventsAsync(startUtc, endUtc, cancellationToken);
     }
 
+    /// <summary>
+    /// Sends a single <see cref="HistorianEvent"/> to the Historian's built-in CM_EVENT tag
+    /// over the WCF event pipeline (Open2 event mode → CM_EVENT registration → AddS2). The
+    /// event is appended to the historian's event history and is readable back via
+    /// <see cref="ReadEventsAsync"/> / the <c>v_AlarmEventHistory2</c> view. Only original
+    /// events (<see cref="HistorianEvent.RevisionVersion"/> = 0) with string-valued properties
+    /// are supported; other property value types and revision/update/delete events throw
+    /// <see cref="ProtocolEvidenceMissingException"/> until their wire encoding is captured.
+    /// </summary>
+    public Task<bool> SendEventAsync(HistorianEvent historianEvent, CancellationToken cancellationToken = default)
+    {
+        ArgumentNullException.ThrowIfNull(historianEvent);
+        return new HistorianWcfEventOrchestrator(_options).SendEventAsync(historianEvent, cancellationToken);
+    }
+
     public IAsyncEnumerable<string> BrowseTagNamesAsync(string filter = "*", CancellationToken cancellationToken = default)
     {
         ArgumentException.ThrowIfNullOrWhiteSpace(filter);