feat(grpc-events): v6 StartEventQuery request + capture-event harness scenario

Captured the stock 2023 R2 client doing a gRPC event read (50 rows flowed) to
resolve the open "gRPC event ROW retrieval returns zero rows" item. Two captured
differences from our SDK's path; this lands the first (necessary) one plus the
capture tooling.

- HistorianEventQueryProtocol.CreateStartEventQueryAttempts: add a `version`
  parameter (default 5 = the 2020 WCF format, unchanged). The gRPC event
  orchestrator now opts into version 6 — the leading `06` plus a 5-byte trailing
  zero pad — which is the envelope the stock 2023 R2 client sends. The two
  buffers are otherwise byte-identical (filter block, UTC string, metadata
  namespace). Golden test Version6EmptyFilterMatchesCapturedGrpcEnvelope pins it.
- Grpc2023CaptureHarness: new `capture-event` scenario drives HistorianAccess
  over an Event-type gRPC connection (CreateEventQuery -> EventQueryArgs ->
  StartQuery -> MoveNext) so the wide-net instrument-grpc-nonstream rewrite dumps
  StartEventQuery.requestBuffer + the row result. Hostname defaults sanitized to
  HISTORIAN_GRPC_HOST / "localhost" (removed hardcoded server name).

NECESSARY BUT NOT SUFFICIENT: live validation shows v6 alone does not make rows
flow — the read also requires an Event-type connection, which our SDK's v6 Open2
format cannot express (see the companion docs commit). The gated
ReadEventsAsync_OverGrpc_* test correctly still pins the no-row throw. 322/322
offline tests pass; WCF event path unchanged.

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

src/AVEVA.Historian.Client/Grpc/HistorianGrpcEventOrchestrator.cs

@@ -266,11 +266,17 @@ internal sealed class HistorianGrpcEventOrchestrator
             new GrpcRetrieval.GetRetrievalInterfaceVersionRequest(), connection.Metadata, Deadline(), cancellationToken);
         HistorianServerVersionGate.Validate(HistorianServiceInterface.Retrieval, retrievalVersion.UiVersion, _options);
 
+        // Version 6 envelope: the stock 2023 R2 client sends v6 (the WCF path's v5 request is accepted
+        // here but is the legacy format). NECESSARY but not alone sufficient — live validation 2026-06-22
+        // showed rows still don't flow on v6 because the read also requires an EVENT-type connection
+        // (the stock client opens ConnectionType=Event; our OpenSession opens a Process-style 0x402
+        // session). See docs/reverse-engineering/grpc-event-query-capture.md "remaining gate".
         IReadOnlyList<HistorianEventQueryAttempt> attempts = HistorianEventQueryProtocol.CreateStartEventQueryAttempts(
             startUtc.ToUniversalTime(),
             endUtc.ToUniversalTime(),
             eventCount: 5,
-            filter);
+            filter,
+            version: 6);
         byte[] requestBuffer = attempts[0].RequestBuffer;
 
         GrpcRetrieval.StartEventQueryResponse startResponse = retrievalClient.StartEventQuery(