diff --git a/src/ScadaLink.AuditLog/Central/AuditLogIngestActor.cs b/src/ScadaLink.AuditLog/Central/AuditLogIngestActor.cs
index 01496bb..2b2c580 100644
--- a/src/ScadaLink.AuditLog/Central/AuditLogIngestActor.cs
+++ b/src/ScadaLink.AuditLog/Central/AuditLogIngestActor.cs
@@ -4,6 +4,7 @@ using Microsoft.Extensions.Logging;
 using ScadaLink.Commons.Entities.Audit;
 using ScadaLink.Commons.Interfaces.Repositories;
 using ScadaLink.Commons.Messages.Audit;
+using ScadaLink.ConfigurationDatabase;
 
 namespace ScadaLink.AuditLog.Central;
 
@@ -61,6 +62,11 @@ public class AuditLogIngestActor : ReceiveActor
         _logger = logger;
 
         ReceiveAsync<IngestAuditEventsCommand>(OnIngestAsync);
+        // The single-repository test ctor cannot service the M3 dual-write —
+        // it has no SiteCalls repo and no DbContext. The handler still
+        // registers (so callers don't dead-letter) but replies empty so the
+        // test surface stays explicit about what this ctor supports.
+        ReceiveAsync<IngestCachedTelemetryCommand>(OnCachedTelemetryWithoutDualWriteAsync);
     }
 
     /// <summary>
@@ -81,6 +87,7 @@ public class AuditLogIngestActor : ReceiveActor
         _logger = logger;
 
         ReceiveAsync<IngestAuditEventsCommand>(OnIngestAsync);
+        ReceiveAsync<IngestCachedTelemetryCommand>(OnCachedTelemetryAsync);
     }
 
     /// <summary>
@@ -150,4 +157,98 @@ public class AuditLogIngestActor : ReceiveActor
 
         replyTo.Tell(new IngestAuditEventsReply(accepted));
     }
+
+    /// <summary>
+    /// M3 dual-write handler. For every <see cref="CachedTelemetryEntry"/> the
+    /// actor opens a fresh MS SQL transaction, inserts the AuditLog row
+    /// idempotently AND upserts the SiteCalls row monotonically. Both succeed
+    /// or both roll back, so the audit and operational mirrors never drift
+    /// mid-row. The IngestedAtUtc stamp is unified between the two rows so a
+    /// downstream join lines up cleanly.
+    /// </summary>
+    /// <remarks>
+    /// Per-entry isolation — one entry's failed transaction does NOT abort
+    /// other entries in the batch (each gets its own
+    /// <see cref="Microsoft.EntityFrameworkCore.RelationalDatabaseFacadeExtensions.BeginTransactionAsync"/>
+    /// scope and a try/catch around it). Audit-write failure NEVER aborts the
+    /// user-facing action — the site keeps the row Pending and retries on the
+    /// next drain.
+    /// </remarks>
+    private async Task OnCachedTelemetryAsync(IngestCachedTelemetryCommand cmd)
+    {
+        var replyTo = Sender;
+        var accepted = new List<Guid>(cmd.Entries.Count);
+
+        try
+        {
+            await using var scope = _serviceProvider!.CreateAsyncScope();
+            var auditRepo = scope.ServiceProvider.GetRequiredService<IAuditLogRepository>();
+            var siteCallRepo = scope.ServiceProvider.GetRequiredService<ISiteCallAuditRepository>();
+            var dbContext = scope.ServiceProvider.GetRequiredService<ScadaLinkDbContext>();
+
+            foreach (var entry in cmd.Entries)
+            {
+                try
+                {
+                    await using var tx = await dbContext.Database
+                        .BeginTransactionAsync()
+                        .ConfigureAwait(false);
+
+                    // Stamp IngestedAtUtc on both rows from a single
+                    // central-side instant so a join on the two tables sees
+                    // matching timestamps (debugging convenience, not a
+                    // correctness invariant).
+                    var ingestedAt = DateTime.UtcNow;
+                    var auditStamped = entry.Audit with { IngestedAtUtc = ingestedAt };
+                    var siteCallStamped = entry.SiteCall with { IngestedAtUtc = ingestedAt };
+
+                    await auditRepo.InsertIfNotExistsAsync(auditStamped)
+                        .ConfigureAwait(false);
+                    await siteCallRepo.UpsertAsync(siteCallStamped)
+                        .ConfigureAwait(false);
+
+                    await tx.CommitAsync().ConfigureAwait(false);
+                    accepted.Add(entry.Audit.EventId);
+                }
+                catch (Exception ex)
+                {
+                    // Both rows rolled back via the disposing transaction. The
+                    // EventId is NOT added to `accepted` so the site keeps its
+                    // row Pending and retries on the next drain. Other entries
+                    // in the batch continue with their own transactions.
+                    _logger.LogError(
+                        ex,
+                        "Combined telemetry dual-write failed for AuditEvent {EventId} / TrackedOperationId {TrackedOpId}; rolled back.",
+                        entry.Audit.EventId,
+                        entry.SiteCall.TrackedOperationId);
+                }
+            }
+        }
+        catch (Exception ex)
+        {
+            // Resolving the scope itself threw (e.g. DI mis-wiring). Log and
+            // reply with whatever we managed to accept (likely empty) — the
+            // central singleton MUST stay alive.
+            _logger.LogError(
+                ex,
+                "Combined telemetry batch ingest failed before per-entry processing.");
+        }
+
+        replyTo.Tell(new IngestCachedTelemetryReply(accepted));
+    }
+
+    /// <summary>
+    /// Fallback handler installed on the single-repository test ctor — that
+    /// ctor has no DbContext and no <see cref="ISiteCallAuditRepository"/>, so
+    /// it cannot service the dual-write. Logs a warning and replies with an
+    /// empty ack so callers fall through to their retry path.
+    /// </summary>
+    private Task OnCachedTelemetryWithoutDualWriteAsync(IngestCachedTelemetryCommand cmd)
+    {
+        _logger.LogWarning(
+            "AuditLogIngestActor received IngestCachedTelemetryCommand on the single-repository ctor; dual-write requires the IServiceProvider ctor. Replying with empty ack ({Count} entries).",
+            cmd.Entries.Count);
+        Sender.Tell(new IngestCachedTelemetryReply(Array.Empty<Guid>()));
+        return Task.CompletedTask;
+    }
 }
diff --git a/src/ScadaLink.Commons/Messages/Audit/IngestCachedTelemetryCommand.cs b/src/ScadaLink.Commons/Messages/Audit/IngestCachedTelemetryCommand.cs
new file mode 100644
index 0000000..e7c63a1
--- /dev/null
+++ b/src/ScadaLink.Commons/Messages/Audit/IngestCachedTelemetryCommand.cs
@@ -0,0 +1,30 @@
+using ScadaLink.Commons.Entities.Audit;
+
+namespace ScadaLink.Commons.Messages.Audit;
+
+/// <summary>
+/// Akka message sent to the central <c>AuditLogIngestActor</c> (Audit Log #23 M3
+/// Bundle D dual-write transaction) carrying a batch of combined audit +
+/// site-call telemetry packets decoded by the <c>SiteStreamGrpcServer</c> from a
+/// site's <c>IngestCachedTelemetry</c> gRPC RPC. For each entry the actor writes
+/// the <see cref="AuditEvent"/> row AND the <see cref="SiteCall"/> upsert inside
+/// a single MS SQL transaction — both succeed or both roll back, so the audit
+/// and operational mirrors never drift mid-row.
+/// </summary>
+/// <remarks>
+/// Lives in <c>ScadaLink.Commons</c> for the same reason as
+/// <c>IngestAuditEventsCommand</c>: the gRPC server in
+/// <c>ScadaLink.Communication</c> constructs it and <c>ScadaLink.AuditLog</c>
+/// already references Communication. Putting the message in Commons avoids a
+/// project-reference cycle.
+/// </remarks>
+public sealed record IngestCachedTelemetryCommand(IReadOnlyList<CachedTelemetryEntry> Entries);
+
+/// <summary>
+/// One lifecycle event of a cached call: the <see cref="AuditEvent"/> to insert
+/// (idempotent on <see cref="AuditEvent.EventId"/>) plus the
+/// <see cref="SiteCall"/> to upsert (monotonic on
+/// <see cref="SiteCall.TrackedOperationId"/>). The two rows are paired so the
+/// central dual-write transaction can commit them atomically.
+/// </summary>
+public sealed record CachedTelemetryEntry(AuditEvent Audit, SiteCall SiteCall);
diff --git a/src/ScadaLink.Commons/Messages/Audit/IngestCachedTelemetryReply.cs b/src/ScadaLink.Commons/Messages/Audit/IngestCachedTelemetryReply.cs
new file mode 100644
index 0000000..1de259d
--- /dev/null
+++ b/src/ScadaLink.Commons/Messages/Audit/IngestCachedTelemetryReply.cs
@@ -0,0 +1,10 @@
+namespace ScadaLink.Commons.Messages.Audit;
+
+/// <summary>
+/// Reply from the central <c>AuditLogIngestActor</c> for an
+/// <see cref="IngestCachedTelemetryCommand"/>. <see cref="AcceptedEventIds"/>
+/// lists every entry whose dual-write transaction (AuditLog INSERT + SiteCalls
+/// UPSERT) committed; entries whose transaction rolled back are absent so the
+/// site can leave the row Pending and retry on the next drain.
+/// </summary>
+public sealed record IngestCachedTelemetryReply(IReadOnlyList<Guid> AcceptedEventIds);
diff --git a/src/ScadaLink.Communication/Grpc/SiteStreamGrpcServer.cs b/src/ScadaLink.Communication/Grpc/SiteStreamGrpcServer.cs
index 71560c3..1da14ec 100644
--- a/src/ScadaLink.Communication/Grpc/SiteStreamGrpcServer.cs
+++ b/src/ScadaLink.Communication/Grpc/SiteStreamGrpcServer.cs
@@ -6,6 +6,7 @@ using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
 using ScadaLink.Commons.Entities.Audit;
 using ScadaLink.Commons.Messages.Audit;
+using ScadaLink.Commons.Types;
 using ScadaLink.Commons.Types.Enums;
 using GrpcStatus = Grpc.Core.Status;
 
@@ -298,9 +299,132 @@ public class SiteStreamGrpcServer : SiteStreamService.SiteStreamServiceBase
         return ack;
     }
 
+    /// <summary>
+    /// Audit Log (#23) M3 site→central combined-telemetry push RPC. Decodes a
+    /// batch of <see cref="CachedTelemetryPacket"/> entries into matched
+    /// (AuditEvent, SiteCall) pairs, Asks the central <c>AuditLogIngestActor</c>
+    /// proxy to persist them in dual-write transactions, and echoes the
+    /// AuditEvent EventIds that committed back so the site can flip its local
+    /// rows to <c>Forwarded</c>.
+    /// </summary>
+    /// <remarks>
+    /// Same wiring-incomplete fallback as <see cref="IngestAuditEvents"/>: when
+    /// the actor proxy has not been set the RPC replies with an empty ack so
+    /// sites treat the outcome as transient and retry, never a hard fault.
+    /// </remarks>
+    public override async Task<IngestAck> IngestCachedTelemetry(
+        CachedTelemetryBatch request,
+        ServerCallContext context)
+    {
+        if (request.Packets.Count == 0)
+        {
+            return new IngestAck();
+        }
+
+        var actor = _auditIngestActor;
+        if (actor is null)
+        {
+            _logger.LogWarning(
+                "IngestCachedTelemetry received {Count} packets before SetAuditIngestActor was called; returning empty ack.",
+                request.Packets.Count);
+            return new IngestAck();
+        }
+
+        var entries = new List<CachedTelemetryEntry>(request.Packets.Count);
+        foreach (var packet in request.Packets)
+        {
+            var auditEvent = MapAuditEventFromDto(packet.AuditEvent);
+            var siteCall = MapSiteCallFromDto(packet.Operational);
+            entries.Add(new CachedTelemetryEntry(auditEvent, siteCall));
+        }
+
+        var cmd = new IngestCachedTelemetryCommand(entries);
+        IngestCachedTelemetryReply reply;
+        try
+        {
+            reply = await actor.Ask<IngestCachedTelemetryReply>(
+                cmd, AuditIngestAskTimeout, context.CancellationToken);
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex,
+                "AuditLogIngestActor Ask failed for combined telemetry batch of {Count} packets; returning empty ack.",
+                request.Packets.Count);
+            return new IngestAck();
+        }
+
+        var ack = new IngestAck();
+        foreach (var id in reply.AcceptedEventIds)
+        {
+            ack.AcceptedEventIds.Add(id.ToString());
+        }
+        return ack;
+    }
+
     private static string? NullIfEmpty(string? value) =>
         string.IsNullOrEmpty(value) ? null : value;
 
+    /// <summary>
+    /// Inlined audit-event DTO→entity translation, kept in sync with the
+    /// <see cref="IngestAuditEvents"/> handler above. Extracted to a private
+    /// helper so the M3 dual-write RPC can reuse it without duplicating yet
+    /// another copy. The shape still mirrors
+    /// <c>AuditEventMapper.FromDto</c> in <c>ScadaLink.AuditLog.Telemetry</c>;
+    /// the two must evolve together (the project-reference cycle that
+    /// prevents calling the AuditLog mapper directly is documented on
+    /// <see cref="IngestAuditEvents"/>).
+    /// </summary>
+    private static AuditEvent MapAuditEventFromDto(AuditEventDto dto) =>
+        new()
+        {
+            EventId = Guid.Parse(dto.EventId),
+            OccurredAtUtc = DateTime.SpecifyKind(dto.OccurredAtUtc.ToDateTime(), DateTimeKind.Utc),
+            IngestedAtUtc = null,
+            Channel = Enum.Parse<AuditChannel>(dto.Channel),
+            Kind = Enum.Parse<AuditKind>(dto.Kind),
+            CorrelationId = NullIfEmpty(dto.CorrelationId) is { } cid ? Guid.Parse(cid) : null,
+            SourceSiteId = NullIfEmpty(dto.SourceSiteId),
+            SourceInstanceId = NullIfEmpty(dto.SourceInstanceId),
+            SourceScript = NullIfEmpty(dto.SourceScript),
+            Actor = NullIfEmpty(dto.Actor),
+            Target = NullIfEmpty(dto.Target),
+            Status = Enum.Parse<AuditStatus>(dto.Status),
+            HttpStatus = dto.HttpStatus,
+            DurationMs = dto.DurationMs,
+            ErrorMessage = NullIfEmpty(dto.ErrorMessage),
+            ErrorDetail = NullIfEmpty(dto.ErrorDetail),
+            RequestSummary = NullIfEmpty(dto.RequestSummary),
+            ResponseSummary = NullIfEmpty(dto.ResponseSummary),
+            PayloadTruncated = dto.PayloadTruncated,
+            Extra = NullIfEmpty(dto.Extra),
+            ForwardState = null,
+        };
+
+    /// <summary>
+    /// Translates a <see cref="SiteCallOperationalDto"/> into the persistence
+    /// entity. <see cref="SiteCall.IngestedAtUtc"/> is stamped here as a
+    /// placeholder; the central ingest actor overwrites it inside the
+    /// dual-write transaction so the AuditLog and SiteCalls rows share one
+    /// instant.
+    /// </summary>
+    private static SiteCall MapSiteCallFromDto(SiteCallOperationalDto dto) => new()
+    {
+        TrackedOperationId = TrackedOperationId.Parse(dto.TrackedOperationId),
+        Channel = dto.Channel,
+        Target = dto.Target,
+        SourceSite = dto.SourceSite,
+        Status = dto.Status,
+        RetryCount = dto.RetryCount,
+        LastError = string.IsNullOrEmpty(dto.LastError) ? null : dto.LastError,
+        HttpStatus = dto.HttpStatus,
+        CreatedAtUtc = DateTime.SpecifyKind(dto.CreatedAtUtc.ToDateTime(), DateTimeKind.Utc),
+        UpdatedAtUtc = DateTime.SpecifyKind(dto.UpdatedAtUtc.ToDateTime(), DateTimeKind.Utc),
+        TerminalAtUtc = dto.TerminalAtUtc is null
+            ? null
+            : DateTime.SpecifyKind(dto.TerminalAtUtc.ToDateTime(), DateTimeKind.Utc),
+        IngestedAtUtc = DateTime.UtcNow, // overwritten by AuditLogIngestActor
+    };
+
     /// <summary>
     /// Tracks a single active stream so cleanup only removes its own entry.
     /// </summary>
diff --git a/tests/ScadaLink.AuditLog.Tests/Central/AuditLogIngestActorCombinedTelemetryTests.cs b/tests/ScadaLink.AuditLog.Tests/Central/AuditLogIngestActorCombinedTelemetryTests.cs
new file mode 100644
index 0000000..f61d1cd
--- /dev/null
+++ b/tests/ScadaLink.AuditLog.Tests/Central/AuditLogIngestActorCombinedTelemetryTests.cs
@@ -0,0 +1,391 @@
+using Akka.Actor;
+using Akka.TestKit.Xunit2;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Logging.Abstractions;
+using ScadaLink.AuditLog.Central;
+using ScadaLink.Commons.Entities.Audit;
+using ScadaLink.Commons.Interfaces.Repositories;
+using ScadaLink.Commons.Messages.Audit;
+using ScadaLink.Commons.Types;
+using ScadaLink.Commons.Types.Audit;
+using ScadaLink.Commons.Types.Enums;
+using ScadaLink.ConfigurationDatabase;
+using ScadaLink.ConfigurationDatabase.Repositories;
+using ScadaLink.ConfigurationDatabase.Tests.Migrations;
+
+namespace ScadaLink.AuditLog.Tests.Central;
+
+/// <summary>
+/// Bundle D D2 tests for <see cref="AuditLogIngestActor"/>'s M3 combined-
+/// telemetry dual-write transaction. Uses the same <see cref="MsSqlMigrationFixture"/>
+/// as the M1 + M2 repository tests so the actor exercises real
+/// <see cref="AuditLogRepository.InsertIfNotExistsAsync"/> +
+/// <see cref="SiteCallAuditRepository.UpsertAsync"/> against a per-test MSSQL
+/// database. The transaction commits or rolls back inside one
+/// <see cref="DbContext.Database"/>.
+/// </summary>
+public class AuditLogIngestActorCombinedTelemetryTests : TestKit, IClassFixture<MsSqlMigrationFixture>
+{
+    private readonly MsSqlMigrationFixture _fixture;
+
+    public AuditLogIngestActorCombinedTelemetryTests(MsSqlMigrationFixture fixture)
+    {
+        _fixture = fixture;
+    }
+
+    private ScadaLinkDbContext CreateReadContext()
+    {
+        var options = new DbContextOptionsBuilder<ScadaLinkDbContext>()
+            .UseSqlServer(_fixture.ConnectionString)
+            .Options;
+        return new ScadaLinkDbContext(options);
+    }
+
+    private static string NewSiteId() =>
+        "test-bundle-d2-cached-" + Guid.NewGuid().ToString("N").Substring(0, 8);
+
+    private static (AuditEvent audit, SiteCall siteCall) NewEntry(
+        string siteId,
+        TrackedOperationId? trackedOperationId = null,
+        Guid? eventId = null,
+        string status = "Submitted",
+        AuditStatus auditStatus = AuditStatus.Submitted)
+    {
+        var trackedId = trackedOperationId ?? TrackedOperationId.New();
+        var now = new DateTime(2026, 5, 20, 10, 0, 0, DateTimeKind.Utc);
+
+        var audit = new AuditEvent
+        {
+            EventId = eventId ?? Guid.NewGuid(),
+            OccurredAtUtc = now,
+            Channel = AuditChannel.ApiOutbound,
+            Kind = AuditKind.CachedSubmit,
+            Status = auditStatus,
+            SourceSiteId = siteId,
+            CorrelationId = trackedId.Value,
+        };
+
+        var siteCall = new SiteCall
+        {
+            TrackedOperationId = trackedId,
+            Channel = "ApiOutbound",
+            Target = "ERP.GetOrder",
+            SourceSite = siteId,
+            Status = status,
+            RetryCount = 0,
+            CreatedAtUtc = now,
+            UpdatedAtUtc = now,
+            IngestedAtUtc = now, // overwritten by the actor
+        };
+
+        return (audit, siteCall);
+    }
+
+    /// <summary>
+    /// Builds a minimal DI container around the per-test MSSQL fixture's
+    /// connection string — DbContext + the two repositories the dual-write
+    /// handler resolves. Mirrors AddConfigurationDatabase without the
+    /// DataProtection wiring (we never write secret columns in these tests).
+    /// </summary>
+    private IServiceProvider BuildServiceProvider(
+        Func<ScadaLinkDbContext, ISiteCallAuditRepository>? siteCallRepoFactory = null)
+    {
+        var services = new ServiceCollection();
+        services.AddDbContext<ScadaLinkDbContext>(opts =>
+            opts.UseSqlServer(_fixture.ConnectionString)
+                .ConfigureWarnings(w => w.Ignore(
+                    Microsoft.EntityFrameworkCore.Diagnostics.RelationalEventId.PendingModelChangesWarning)));
+        services.AddScoped<IAuditLogRepository>(sp =>
+            new AuditLogRepository(sp.GetRequiredService<ScadaLinkDbContext>()));
+        if (siteCallRepoFactory is null)
+        {
+            services.AddScoped<ISiteCallAuditRepository>(sp =>
+                new SiteCallAuditRepository(sp.GetRequiredService<ScadaLinkDbContext>()));
+        }
+        else
+        {
+            services.AddScoped(sp =>
+                siteCallRepoFactory(sp.GetRequiredService<ScadaLinkDbContext>()));
+        }
+        return services.BuildServiceProvider();
+    }
+
+    private IActorRef CreateActor(IServiceProvider serviceProvider) =>
+        Sys.ActorOf(Props.Create(() => new AuditLogIngestActor(
+            serviceProvider,
+            NullLogger<AuditLogIngestActor>.Instance)));
+
+    [SkippableFact]
+    public async Task Receive_OneCachedPacket_WritesAuditRow_AND_SiteCallRow_AcksId()
+    {
+        Skip.IfNot(_fixture.Available, _fixture.SkipReason);
+
+        var siteId = NewSiteId();
+        var (audit, siteCall) = NewEntry(siteId);
+
+        var sp = BuildServiceProvider();
+        var actor = CreateActor(sp);
+
+        actor.Tell(
+            new IngestCachedTelemetryCommand(new[] { new CachedTelemetryEntry(audit, siteCall) }),
+            TestActor);
+
+        var reply = ExpectMsg<IngestCachedTelemetryReply>(TimeSpan.FromSeconds(15));
+        Assert.Single(reply.AcceptedEventIds);
+        Assert.Equal(audit.EventId, reply.AcceptedEventIds[0]);
+
+        // Verify rows landed in both tables.
+        await using var read = CreateReadContext();
+        var auditRow = await read.Set<AuditEvent>().SingleOrDefaultAsync(e => e.EventId == audit.EventId);
+        Assert.NotNull(auditRow);
+        Assert.NotNull(auditRow!.IngestedAtUtc);
+
+        var siteCallRow = await read.Set<SiteCall>()
+            .SingleOrDefaultAsync(s => s.TrackedOperationId == siteCall.TrackedOperationId);
+        Assert.NotNull(siteCallRow);
+        Assert.Equal(siteCall.Status, siteCallRow!.Status);
+    }
+
+    [SkippableFact]
+    public async Task Receive_DuplicateEventId_SameStatus_NoOp_RowCountUnchanged_AcksId()
+    {
+        Skip.IfNot(_fixture.Available, _fixture.SkipReason);
+
+        var siteId = NewSiteId();
+        var trackedId = TrackedOperationId.New();
+        var eventId = Guid.NewGuid();
+        var (audit, siteCall) = NewEntry(siteId, trackedId, eventId);
+
+        var sp = BuildServiceProvider();
+        var actor = CreateActor(sp);
+
+        // First write
+        actor.Tell(
+            new IngestCachedTelemetryCommand(new[] { new CachedTelemetryEntry(audit, siteCall) }),
+            TestActor);
+        ExpectMsg<IngestCachedTelemetryReply>(TimeSpan.FromSeconds(15));
+
+        // Second write — same EventId and TrackedOperationId, same status. Both
+        // the audit insert (idempotent) and the SiteCalls upsert (monotonic
+        // same-rank → no-op) should silently do nothing while still acking.
+        actor.Tell(
+            new IngestCachedTelemetryCommand(new[] { new CachedTelemetryEntry(audit, siteCall) }),
+            TestActor);
+        var reply = ExpectMsg<IngestCachedTelemetryReply>(TimeSpan.FromSeconds(15));
+
+        Assert.Single(reply.AcceptedEventIds);
+        Assert.Equal(eventId, reply.AcceptedEventIds[0]);
+
+        await using var read = CreateReadContext();
+        var auditCount = await read.Set<AuditEvent>().CountAsync(e => e.EventId == eventId);
+        Assert.Equal(1, auditCount);
+
+        var siteCallCount = await read.Set<SiteCall>()
+            .CountAsync(s => s.TrackedOperationId == trackedId);
+        Assert.Equal(1, siteCallCount);
+    }
+
+    [SkippableFact]
+    public async Task Receive_DuplicateEventId_AdvancedSiteCallStatus_UpdatesSiteCall()
+    {
+        Skip.IfNot(_fixture.Available, _fixture.SkipReason);
+
+        var siteId = NewSiteId();
+        var trackedId = TrackedOperationId.New();
+
+        var sp = BuildServiceProvider();
+        var actor = CreateActor(sp);
+
+        // 1st packet — Submitted (audit EventId #1, SiteCalls Status=Submitted).
+        var (auditSubmit, siteCallSubmit) = NewEntry(
+            siteId, trackedId, status: "Submitted", auditStatus: AuditStatus.Submitted);
+        actor.Tell(
+            new IngestCachedTelemetryCommand(new[] { new CachedTelemetryEntry(auditSubmit, siteCallSubmit) }),
+            TestActor);
+        ExpectMsg<IngestCachedTelemetryReply>(TimeSpan.FromSeconds(15));
+
+        // 2nd packet — Attempted with retry count 1 (audit EventId #2,
+        // SiteCalls Status=Attempted — monotonic upsert wins). Same
+        // TrackedOperationId throughout.
+        var (auditAttempt, siteCallAttempt) = NewEntry(
+            siteId, trackedId, status: "Attempted", auditStatus: AuditStatus.Attempted);
+        var advanced = siteCallAttempt with { RetryCount = 1, UpdatedAtUtc = siteCallAttempt.UpdatedAtUtc.AddMinutes(1) };
+        actor.Tell(
+            new IngestCachedTelemetryCommand(new[] { new CachedTelemetryEntry(auditAttempt, advanced) }),
+            TestActor);
+        var reply = ExpectMsg<IngestCachedTelemetryReply>(TimeSpan.FromSeconds(15));
+
+        Assert.Single(reply.AcceptedEventIds);
+        Assert.Equal(auditAttempt.EventId, reply.AcceptedEventIds[0]);
+
+        // Both audit rows exist.
+        await using var read = CreateReadContext();
+        var auditRows = await read.Set<AuditEvent>()
+            .Where(e => e.SourceSiteId == siteId)
+            .ToListAsync();
+        Assert.Equal(2, auditRows.Count);
+
+        // SiteCalls row advanced to Attempted with retry count 1.
+        var siteCallRow = await read.Set<SiteCall>()
+            .SingleAsync(s => s.TrackedOperationId == trackedId);
+        Assert.Equal("Attempted", siteCallRow.Status);
+        Assert.Equal(1, siteCallRow.RetryCount);
+    }
+
+    [SkippableFact]
+    public async Task Receive_AuditInsertSucceeds_SiteCallThrows_BothRolledBack_NoOrphanRow()
+    {
+        Skip.IfNot(_fixture.Available, _fixture.SkipReason);
+
+        var siteId = NewSiteId();
+        var (audit, siteCall) = NewEntry(siteId);
+
+        // Wrap the SiteCalls repo so UpsertAsync always throws — the dual-write
+        // transaction must roll back the AuditLog INSERT done in the same
+        // transaction, leaving no orphan row.
+        var sp = BuildServiceProvider(
+            ctx => new ThrowingSiteCallRepo(new SiteCallAuditRepository(ctx)));
+        var actor = CreateActor(sp);
+
+        actor.Tell(
+            new IngestCachedTelemetryCommand(new[] { new CachedTelemetryEntry(audit, siteCall) }),
+            TestActor);
+
+        var reply = ExpectMsg<IngestCachedTelemetryReply>(TimeSpan.FromSeconds(15));
+        Assert.Empty(reply.AcceptedEventIds);
+
+        await using var read = CreateReadContext();
+        var auditRow = await read.Set<AuditEvent>().SingleOrDefaultAsync(e => e.EventId == audit.EventId);
+        Assert.Null(auditRow);
+
+        var siteCallRow = await read.Set<SiteCall>()
+            .SingleOrDefaultAsync(s => s.TrackedOperationId == siteCall.TrackedOperationId);
+        Assert.Null(siteCallRow);
+    }
+
+    [SkippableFact]
+    public async Task Receive_FiveCachedPackets_AllPersistedSeparately_AllAcked()
+    {
+        Skip.IfNot(_fixture.Available, _fixture.SkipReason);
+
+        var siteId = NewSiteId();
+        var entries = Enumerable.Range(0, 5).Select(_ =>
+        {
+            var (audit, siteCall) = NewEntry(siteId);
+            return new CachedTelemetryEntry(audit, siteCall);
+        }).ToList();
+
+        var sp = BuildServiceProvider();
+        var actor = CreateActor(sp);
+
+        actor.Tell(new IngestCachedTelemetryCommand(entries), TestActor);
+
+        var reply = ExpectMsg<IngestCachedTelemetryReply>(TimeSpan.FromSeconds(15));
+        Assert.Equal(5, reply.AcceptedEventIds.Count);
+        Assert.True(entries.Select(e => e.Audit.EventId).ToHashSet()
+            .SetEquals(reply.AcceptedEventIds.ToHashSet()));
+
+        await using var read = CreateReadContext();
+        var auditCount = await read.Set<AuditEvent>().CountAsync(e => e.SourceSiteId == siteId);
+        Assert.Equal(5, auditCount);
+
+        var siteCallCount = await read.Set<SiteCall>().CountAsync(s => s.SourceSite == siteId);
+        Assert.Equal(5, siteCallCount);
+    }
+
+    [SkippableFact]
+    public async Task Receive_OnePacketSucceeds_NextPacketThrows_FirstStillCommitted_BatchContinues()
+    {
+        Skip.IfNot(_fixture.Available, _fixture.SkipReason);
+
+        var siteId = NewSiteId();
+        var (audit1, siteCall1) = NewEntry(siteId);
+        var (audit2, siteCall2) = NewEntry(siteId);
+        var (audit3, siteCall3) = NewEntry(siteId);
+        var poisonTrackedId = siteCall2.TrackedOperationId;
+
+        // Throw only for the middle entry's TrackedOperationId — entries on
+        // either side must commit their own transactions independently.
+        var sp = BuildServiceProvider(
+            ctx => new PoisonOnIdSiteCallRepo(new SiteCallAuditRepository(ctx), poisonTrackedId));
+        var actor = CreateActor(sp);
+
+        actor.Tell(
+            new IngestCachedTelemetryCommand(new[]
+            {
+                new CachedTelemetryEntry(audit1, siteCall1),
+                new CachedTelemetryEntry(audit2, siteCall2),
+                new CachedTelemetryEntry(audit3, siteCall3),
+            }),
+            TestActor);
+
+        var reply = ExpectMsg<IngestCachedTelemetryReply>(TimeSpan.FromSeconds(15));
+
+        // Two entries committed; poison entry rolled back.
+        Assert.Equal(2, reply.AcceptedEventIds.Count);
+        Assert.Contains(audit1.EventId, reply.AcceptedEventIds);
+        Assert.Contains(audit3.EventId, reply.AcceptedEventIds);
+        Assert.DoesNotContain(audit2.EventId, reply.AcceptedEventIds);
+
+        await using var read = CreateReadContext();
+        var auditRows = await read.Set<AuditEvent>().Where(e => e.SourceSiteId == siteId).ToListAsync();
+        Assert.Equal(2, auditRows.Count);
+        Assert.DoesNotContain(auditRows, r => r.EventId == audit2.EventId);
+
+        var siteCallRows = await read.Set<SiteCall>().Where(s => s.SourceSite == siteId).ToListAsync();
+        Assert.Equal(2, siteCallRows.Count);
+        Assert.DoesNotContain(siteCallRows, r => r.TrackedOperationId == poisonTrackedId);
+    }
+
+    /// <summary>
+    /// Test double — throws unconditionally from <see cref="UpsertAsync"/> so
+    /// the dual-write transaction is forced to roll back. Lets the AuditLog
+    /// row insert succeed in-transaction; the rollback must remove it.
+    /// </summary>
+    private sealed class ThrowingSiteCallRepo : ISiteCallAuditRepository
+    {
+        private readonly ISiteCallAuditRepository _inner;
+        public ThrowingSiteCallRepo(ISiteCallAuditRepository inner) { _inner = inner; }
+        public Task UpsertAsync(SiteCall siteCall, CancellationToken ct = default) =>
+            throw new InvalidOperationException("simulated SiteCalls upsert failure");
+        public Task<SiteCall?> GetAsync(TrackedOperationId id, CancellationToken ct = default) =>
+            _inner.GetAsync(id, ct);
+        public Task<IReadOnlyList<SiteCall>> QueryAsync(
+            SiteCallQueryFilter filter, SiteCallPaging paging, CancellationToken ct = default) =>
+            _inner.QueryAsync(filter, paging, ct);
+        public Task<int> PurgeTerminalAsync(DateTime olderThanUtc, CancellationToken ct = default) =>
+            _inner.PurgeTerminalAsync(olderThanUtc, ct);
+    }
+
+    /// <summary>
+    /// Test double — throws only when the supplied poison TrackedOperationId
+    /// is the one being upserted. Demonstrates per-entry transaction isolation:
+    /// one entry's failed transaction must not abort the batch's other entries.
+    /// </summary>
+    private sealed class PoisonOnIdSiteCallRepo : ISiteCallAuditRepository
+    {
+        private readonly ISiteCallAuditRepository _inner;
+        private readonly TrackedOperationId _poisonId;
+        public PoisonOnIdSiteCallRepo(ISiteCallAuditRepository inner, TrackedOperationId poisonId)
+        {
+            _inner = inner;
+            _poisonId = poisonId;
+        }
+        public Task UpsertAsync(SiteCall siteCall, CancellationToken ct = default)
+        {
+            if (siteCall.TrackedOperationId == _poisonId)
+            {
+                throw new InvalidOperationException("simulated SiteCalls upsert failure for poison id");
+            }
+            return _inner.UpsertAsync(siteCall, ct);
+        }
+        public Task<SiteCall?> GetAsync(TrackedOperationId id, CancellationToken ct = default) =>
+            _inner.GetAsync(id, ct);
+        public Task<IReadOnlyList<SiteCall>> QueryAsync(
+            SiteCallQueryFilter filter, SiteCallPaging paging, CancellationToken ct = default) =>
+            _inner.QueryAsync(filter, paging, ct);
+        public Task<int> PurgeTerminalAsync(DateTime olderThanUtc, CancellationToken ct = default) =>
+            _inner.PurgeTerminalAsync(olderThanUtc, ct);
+    }
+}
diff --git a/tests/ScadaLink.Communication.Tests/SiteStreamIngestCachedTelemetryTests.cs b/tests/ScadaLink.Communication.Tests/SiteStreamIngestCachedTelemetryTests.cs
new file mode 100644
index 0000000..b5194a0
--- /dev/null
+++ b/tests/ScadaLink.Communication.Tests/SiteStreamIngestCachedTelemetryTests.cs
@@ -0,0 +1,121 @@
+using Akka.Actor;
+using Akka.TestKit.Xunit2;
+using Google.Protobuf.WellKnownTypes;
+using Grpc.Core;
+using Microsoft.Extensions.Logging.Abstractions;
+using NSubstitute;
+using ScadaLink.Commons.Messages.Audit;
+using ScadaLink.Communication.Grpc;
+
+namespace ScadaLink.Communication.Tests;
+
+/// <summary>
+/// Bundle D D2 tests for <see cref="SiteStreamGrpcServer.IngestCachedTelemetry"/>.
+/// Verifies the DTO→entity→actor→ack round-trip through the gRPC handler. A
+/// tiny <c>EchoCachedIngestActor</c> stands in for the central
+/// <c>AuditLogIngestActor</c>, replying with the EventIds it received so the
+/// test asserts the wiring without depending on MSSQL.
+/// </summary>
+public class SiteStreamIngestCachedTelemetryTests : TestKit
+{
+    private readonly ISiteStreamSubscriber _subscriber = Substitute.For<ISiteStreamSubscriber>();
+
+    private SiteStreamGrpcServer CreateServer() =>
+        new(_subscriber, NullLogger<SiteStreamGrpcServer>.Instance);
+
+    private static ServerCallContext NewContext(CancellationToken ct = default)
+    {
+        var context = Substitute.For<ServerCallContext>();
+        context.CancellationToken.Returns(ct);
+        return context;
+    }
+
+    private static CachedTelemetryPacket NewPacket(Guid? eventId = null, Guid? trackedId = null)
+    {
+        var now = Timestamp.FromDateTime(
+            DateTime.SpecifyKind(new DateTime(2026, 5, 20, 10, 0, 0), DateTimeKind.Utc));
+        return new CachedTelemetryPacket
+        {
+            AuditEvent = new AuditEventDto
+            {
+                EventId = (eventId ?? Guid.NewGuid()).ToString(),
+                OccurredAtUtc = now,
+                Channel = "ApiOutbound",
+                Kind = "CachedSubmit",
+                Status = "Submitted",
+                SourceSiteId = "site-1",
+                CorrelationId = (trackedId ?? Guid.NewGuid()).ToString(),
+            },
+            Operational = new SiteCallOperationalDto
+            {
+                TrackedOperationId = (trackedId ?? Guid.NewGuid()).ToString(),
+                Channel = "ApiOutbound",
+                Target = "ERP.GetOrder",
+                SourceSite = "site-1",
+                Status = "Submitted",
+                RetryCount = 0,
+                CreatedAtUtc = now,
+                UpdatedAtUtc = now,
+            },
+        };
+    }
+
+    [Fact]
+    public async Task IngestCachedTelemetry_RoutesToActor_ReturnsReply()
+    {
+        // Arrange — stub actor that echoes every received EventId back.
+        var stubActor = Sys.ActorOf(Props.Create(() => new EchoCachedIngestActor()));
+
+        var server = CreateServer();
+        server.SetAuditIngestActor(stubActor);
+
+        var packets = Enumerable.Range(0, 3)
+            .Select(_ => NewPacket())
+            .ToList();
+
+        var batch = new CachedTelemetryBatch();
+        batch.Packets.AddRange(packets);
+
+        // Act
+        var ack = await server.IngestCachedTelemetry(batch, NewContext());
+
+        // Assert — every packet's EventId appears in the ack, demonstrating
+        // end-to-end routing through the actor.
+        Assert.Equal(3, ack.AcceptedEventIds.Count);
+        var expectedIds = packets.Select(p => p.AuditEvent.EventId).ToHashSet();
+        Assert.True(expectedIds.SetEquals(ack.AcceptedEventIds.ToHashSet()));
+    }
+
+    [Fact]
+    public async Task IngestCachedTelemetry_NoActorWired_ReturnsEmptyAck()
+    {
+        var server = CreateServer();
+        // Intentionally do NOT call SetAuditIngestActor — simulates host
+        // startup race window.
+
+        var batch = new CachedTelemetryBatch();
+        batch.Packets.Add(NewPacket());
+
+        var ack = await server.IngestCachedTelemetry(batch, NewContext());
+
+        Assert.Empty(ack.AcceptedEventIds);
+    }
+
+    /// <summary>
+    /// Tiny ReceiveActor that echoes every EventId in an incoming
+    /// <see cref="IngestCachedTelemetryCommand"/> back as an
+    /// <see cref="IngestCachedTelemetryReply"/>. Stands in for the central
+    /// AuditLogIngestActor so this test never touches MSSQL.
+    /// </summary>
+    private sealed class EchoCachedIngestActor : ReceiveActor
+    {
+        public EchoCachedIngestActor()
+        {
+            Receive<IngestCachedTelemetryCommand>(cmd =>
+            {
+                var ids = cmd.Entries.Select(e => e.Audit.EventId).ToList();
+                Sender.Tell(new IngestCachedTelemetryReply(ids));
+            });
+        }
+    }
+}