Phase 7 follow-up #247 — Galaxy.Host historian writer + SQLite sink activation

Closes the historian leg of Phase 7. Scripted alarm transitions now batch-flow
through the existing Galaxy.Host pipe + queue durably in a local SQLite store-
and-forward when Galaxy is the registered driver, instead of being dropped into
NullAlarmHistorianSink.

## GalaxyHistorianWriter (Driver.Galaxy.Proxy.Ipc)

IAlarmHistorianWriter implementation. Translates AlarmHistorianEvent →
HistorianAlarmEventDto (Stream D contract), batches via the existing
GalaxyIpcClient.CallAsync round-trip on MessageKind.HistorianAlarmEventRequest /
Response, maps per-event HistorianAlarmEventOutcomeDto bytes back to
HistorianWriteOutcome (Ack/RetryPlease/PermanentFail) so the SQLite drain
worker knows what to ack vs dead-letter vs retry. Empty-batch fast path.
Pipe-level transport faults (broken pipe, host crash) bubble up as
GalaxyIpcException which the SQLite sink's drain worker translates to
whole-batch RetryPlease per its catch contract.

## GalaxyProxyDriver implements IAlarmHistorianWriter

Marker interface lets Phase7Composer discover it via type check at compose
time. WriteBatchAsync delegates to a thin GalaxyHistorianWriter wrapping the
driver's existing _client. Throws InvalidOperationException if InitializeAsync
hasn't connected yet — the SQLite drain worker treats that as a transient
batch failure and retries.

## Phase7Composer.ResolveHistorianSink

Replaces the injected sink dep when any registered driver implements
IAlarmHistorianWriter. Constructs SqliteStoreAndForwardSink at
%ProgramData%/OtOpcUa/alarm-historian-queue.db (falls back to %TEMP% when
ProgramData unavailable, e.g. dev), starts the 2s drain timer, owns the sink
disposable for clean teardown. When no driver provides the writer, keeps the
NullAlarmHistorianSink wired by Program.cs (#246).

DisposeAsync now also disposes the owned SQLite sink in the right order:
bridge → engines → owned sink → injected fallback.

## Tests — 7 new GalaxyHistorianWriterMappingTests

ToDto round-trips every field; preserves null Comment; per-byte outcome enum
mapping (Ack / RetryPlease / PermanentFail) via [Theory]; unknown byte throws;
ctor null-guard. The IPC round-trip itself is covered by the live Host suite
(task #240) which constructs a real pipe.

Server.Phase7 tests: 34/34 still pass; Galaxy.Proxy tests: 25/25 (+7 = 32 total).

## Phase 7 production wiring chain — COMPLETE
- ✅ #243 composition kernel
- ✅ #245 scripted-alarm IReadable adapter
- ✅ #244 driver bridge
- ✅ #246 Program.cs wire-in
- ✅ #247 this — Galaxy.Host historian writer + SQLite sink activation

What unblocks now: task #240 live OPC UA E2E smoke. With a Galaxy driver
registered, scripted alarm transitions flow end-to-end through the engine →
SQLite queue → drain worker → Galaxy.Host IPC → Aveva Historian alarm schema.
Without Galaxy, NullSink keeps the engines functional and the queue dormant.

src/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Proxy/Ipc/GalaxyHistorianWriter.cs

@@ -0,0 +1,90 @@
+using ZB.MOM.WW.OtOpcUa.Core.AlarmHistorian;
+using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Shared;
+using ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Shared.Contracts;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Proxy.Ipc;
+
+/// <summary>
+///     Phase 7 follow-up (task #247) — bridges <see cref="SqliteStoreAndForwardSink"/>'s
+///     drain worker to <c>Driver.Galaxy.Host</c> over the existing <see cref="GalaxyIpcClient"/>
+///     pipe. Translates <see cref="AlarmHistorianEvent"/> batches into the
+///     <see cref="HistorianAlarmEventDto"/> wire format the Host expects + maps per-event
+///     <see cref="HistorianAlarmEventOutcomeDto"/> responses back to
+///     <see cref="HistorianWriteOutcome"/> so the SQLite queue knows what to ack /
+///     dead-letter / retry.
+/// </summary>
+/// <remarks>
+///     <para>
+///         Reuses the IPC channel <see cref="GalaxyProxyDriver"/> already opens for the
+///         Galaxy data plane — no second pipe to <c>Driver.Galaxy.Host</c>, no separate
+///         auth handshake. The IPC client's call gate serializes historian batches with
+///         driver Reads/Writes/Subscribes; historian batches are infrequent (every few
+///         seconds at most under the SQLite sink's drain cadence) so the contention is
+///         negligible compared to per-tag-read pressure.
+///     </para>
+///     <para>
+///         Pipe-level transport faults (broken pipe, host crash) bubble up as
+///         <see cref="GalaxyIpcException"/> which the SQLite sink's drain worker catches +
+///         translates to a whole-batch RetryPlease per the
+///         <see cref="SqliteStoreAndForwardSink"/> docstring — failed events stay queued
+///         for the next drain tick after backoff.
+///     </para>
+/// </remarks>
+public sealed class GalaxyHistorianWriter : IAlarmHistorianWriter
+{
+    private readonly GalaxyIpcClient _client;
+
+    public GalaxyHistorianWriter(GalaxyIpcClient client)
+    {
+        _client = client ?? throw new ArgumentNullException(nameof(client));
+    }
+
+    public async Task<IReadOnlyList<HistorianWriteOutcome>> WriteBatchAsync(
+        IReadOnlyList<AlarmHistorianEvent> batch, CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(batch);
+        if (batch.Count == 0) return [];
+
+        var request = new HistorianAlarmEventRequest
+        {
+            Events = batch.Select(ToDto).ToArray(),
+        };
+
+        var response = await _client.CallAsync<HistorianAlarmEventRequest, HistorianAlarmEventResponse>(
+            requestKind: MessageKind.HistorianAlarmEventRequest,
+            request: request,
+            expectedResponseKind: MessageKind.HistorianAlarmEventResponse,
+            ct: cancellationToken).ConfigureAwait(false);
+
+        if (response.Outcomes.Length != batch.Count)
+            throw new InvalidOperationException(
+                $"Galaxy.Host returned {response.Outcomes.Length} outcomes for a batch of {batch.Count} — protocol mismatch");
+
+        var outcomes = new HistorianWriteOutcome[response.Outcomes.Length];
+        for (var i = 0; i < response.Outcomes.Length; i++)
+            outcomes[i] = MapOutcome(response.Outcomes[i]);
+        return outcomes;
+    }
+
+    internal static HistorianAlarmEventDto ToDto(AlarmHistorianEvent e) => new()
+    {
+        AlarmId = e.AlarmId,
+        EquipmentPath = e.EquipmentPath,
+        AlarmName = e.AlarmName,
+        AlarmTypeName = e.AlarmTypeName,
+        Severity = (int)e.Severity,
+        EventKind = e.EventKind,
+        Message = e.Message,
+        User = e.User,
+        Comment = e.Comment,
+        TimestampUtcUnixMs = new DateTimeOffset(e.TimestampUtc, TimeSpan.Zero).ToUnixTimeMilliseconds(),
+    };
+
+    internal static HistorianWriteOutcome MapOutcome(HistorianAlarmEventOutcomeDto wire) => wire switch
+    {
+        HistorianAlarmEventOutcomeDto.Ack => HistorianWriteOutcome.Ack,
+        HistorianAlarmEventOutcomeDto.RetryPlease => HistorianWriteOutcome.RetryPlease,
+        HistorianAlarmEventOutcomeDto.PermanentFail => HistorianWriteOutcome.PermanentFail,
+        _ => throw new InvalidOperationException($"Unknown HistorianAlarmEventOutcomeDto byte {(byte)wire}"),
+    };
+}