M3 probe: non-streamed write transaction reachable over 2023 R2 gRPC (Begin/End live-verified)

The D2 storage-engine-pipe wall is WCF-transport-specific. On the 2023 R2 gRPC
front door, TransactionService is a first-class service AND the gateway to the
storage engine, so the Open2 storage-session GUID (uppercase) is accepted
directly as strHandle with no legacy pipe.

Live-verified against the real 2023 R2 server over a write-enabled (0x401) gRPC
session: AddNonStreamValuesBegin returns a real strTransactionId, and
AddNonStreamValuesEnd(bCommit=false) discards it cleanly (no data written). On
2020 WCF the same op returns UnknownClient(51) for every handle + priming chain.

- HistorianGrpcRevisionProbe + grpc-revision-probe CLI command + gated test
  NonStreamedWriteTransaction_OverGrpc_BeginsAndDiscards (live pass).
- HistorianGrpcHandshake.OpenSession gains an optional connectionMode param
  (default read-only 0x402; pass 0x401 for write-enabled) — non-breaking.
- Docs: revision-write-path.md "the wall is gone" section; roadmap M3 section,
  R3.1-R3.3 rows, one-glance table, and status note updated honestly.

Not yet shipped: the AddNonStreamValues btInput VTQ buffer is uncaptured (never
guess wire bytes), so no value-commit is implemented. Scope is non-streamed
ORIGINAL backfill; revision EDITS (R4.2) remain pipe-only even on gRPC.

272 unit tests pass; sanitization scan clean.

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/HistorianGrpcHandshake.cs

@@ -40,10 +40,17 @@ internal static class HistorianGrpcHandshake
         CancellationToken cancellationToken)
         => OpenSession(connection, options, cancellationToken).ClientHandle;
 
+    /// <param name="connectionMode">
+    /// The native Open2 connection mode. Defaults to read-only (<c>0x402</c>); pass
+    /// <see cref="HistorianWcfAuthChainHelper.NativeIntegratedWriteEnabledConnectionMode"/>
+    /// (<c>0x401</c>) for write-enabled sessions (e.g. the non-streamed/revision Transaction path,
+    /// which the read-only mode silently rejects with err 132 OperationNotEnabled).
+    /// </param>
     public static Session OpenSession(
         HistorianGrpcConnection connection,
         HistorianClientOptions options,
-        CancellationToken cancellationToken)
+        CancellationToken cancellationToken,
+        uint connectionMode = HistorianWcfAuthChainHelper.NativeIntegratedReadOnlyConnectionMode)
     {
         DateTime Deadline() => DateTime.UtcNow.Add(options.RequestTimeout);
 
@@ -73,7 +80,7 @@ internal static class HistorianGrpcHandshake
             cancellationToken);
 
         byte[] open2Request = HistorianNativeHandshake.BuildOpenConnection3Request(
-            options.Host, contextKey, HistorianWcfAuthChainHelper.NativeIntegratedReadOnlyConnectionMode);
+            options.Host, contextKey, connectionMode);
 
         GrpcHistory.OpenConnectionResponse open2 = historyClient.OpenConnection(
             new GrpcHistory.OpenConnectionRequest { BtConnectionRequest = ByteString.CopyFrom(open2Request) },