diff --git a/src/Core/ZB.MOM.WW.OtOpcUa.Commons/Protos/TelemetryProtoContract.cs b/src/Core/ZB.MOM.WW.OtOpcUa.Commons/Protos/TelemetryProtoContract.cs
new file mode 100644
index 00000000..b251a542
--- /dev/null
+++ b/src/Core/ZB.MOM.WW.OtOpcUa.Commons/Protos/TelemetryProtoContract.cs
@@ -0,0 +1,25 @@
+using ZB.MOM.WW.OtOpcUa.Commons.Protos.Telemetry.V1;
+
+namespace ZB.MOM.WW.OtOpcUa.Commons.Protos;
+
+/// <summary>
+///     The single source of truth for which <see cref="TelemetryEvent.EventOneofCase"/> variants the
+///     Phase 5 telemetry transport actually handles. Both the contract-lock test (which proves this
+///     list stays in lock-step with the generated oneof) and the later oneof↔domain converter
+///     reference this array, so adding a fifth channel to <c>telemetry.proto</c> forces a matching
+///     entry here or the build/test goes red.
+/// </summary>
+public static class TelemetryProtoContract
+{
+    /// <summary>
+    ///     Exactly the four telemetry oneof cases mirrored from the domain records:
+    ///     alerts / script-logs / driver-health / driver-resilience-status.
+    /// </summary>
+    public static readonly TelemetryEvent.EventOneofCase[] HandledCases =
+    [
+        TelemetryEvent.EventOneofCase.AlarmTransition,
+        TelemetryEvent.EventOneofCase.ScriptLog,
+        TelemetryEvent.EventOneofCase.DriverHealth,
+        TelemetryEvent.EventOneofCase.DriverResilience,
+    ];
+}
diff --git a/src/Core/ZB.MOM.WW.OtOpcUa.Commons/Protos/telemetry.proto b/src/Core/ZB.MOM.WW.OtOpcUa.Commons/Protos/telemetry.proto
new file mode 100644
index 00000000..0997fb2e
--- /dev/null
+++ b/src/Core/ZB.MOM.WW.OtOpcUa.Commons/Protos/telemetry.proto
@@ -0,0 +1,83 @@
+syntax = "proto3";
+
+package telemetry.v1;
+
+option csharp_namespace = "ZB.MOM.WW.OtOpcUa.Commons.Protos.Telemetry.V1";
+
+import "google/protobuf/timestamp.proto";
+
+// Per-cluster mesh Phase 5: the four live-telemetry channels that used to fan out over
+// DistributedPubSub (alerts / script-logs / driver-health / driver-resilience-status) now travel over
+// ONE gRPC server-streaming contract. Central dials each driver node and opens Subscribe; the node
+// streams its own live telemetry as a sequence of TelemetryEvent envelopes.
+//
+// Additive-only field evolution: never renumber or reuse a tag; a pre-field peer must read a new
+// field's proto3 default correctly (that is why nullable domain fields are modelled with `optional`
+// for explicit presence). Locked by the contract test in the Commons test project.
+service TelemetryStreamService {
+  rpc Subscribe(TelemetryStreamRequest) returns (stream TelemetryEvent);
+}
+
+message TelemetryStreamRequest {
+  string correlation_id = 1;
+}
+
+message TelemetryEvent {
+  string correlation_id = 1;
+  oneof event {
+    AlarmTransition        alarm_transition  = 2;   // <- "alerts" / AlarmTransitionEvent
+    ScriptLog              script_log        = 3;   // <- "script-logs" / ScriptLogEntry
+    DriverHealth           driver_health     = 4;   // <- "driver-health" / DriverHealthChanged
+    DriverResilienceStatus driver_resilience = 5;   // <- "driver-resilience-status" / DriverResilienceStatusChanged
+  }
+}
+
+// Mirrors ZB.MOM.WW.OtOpcUa.Commons.Messages.Alerts.AlarmTransitionEvent.
+message AlarmTransition {
+  string alarm_id = 1;
+  string equipment_path = 2;
+  string alarm_name = 3;
+  string transition_kind = 4;                             // string in the record (Activated/Cleared/...); kept as string
+  int32 severity = 5;
+  string message = 6;
+  string user = 7;
+  google.protobuf.Timestamp timestamp_utc = 8;
+  string alarm_type_name = 9;                             // record default "AlarmCondition"
+  optional string comment = 10;                           // nullable in the record — presence distinguishes null from ""
+  optional bool historize_to_aveva = 11;                  // bool? in the record — three states (null / true / false)
+  repeated string referencing_equipment_paths = 12;       // null in the record is treated as empty
+}
+
+// Mirrors ZB.MOM.WW.OtOpcUa.Commons.Messages.Logging.ScriptLogEntry.
+message ScriptLog {
+  string script_id = 1;
+  string level = 2;                                       // string in the record (Trace/Debug/Information/...); kept as string
+  string message = 3;
+  google.protobuf.Timestamp timestamp_utc = 4;
+  optional string virtual_tag_id = 5;                     // nullable in the record
+  optional string alarm_id = 6;                           // nullable in the record
+  optional string equipment_id = 7;                       // nullable in the record
+}
+
+// Mirrors ZB.MOM.WW.OtOpcUa.Commons.Messages.Drivers.DriverHealthChanged.
+message DriverHealth {
+  string cluster_id = 1;
+  string driver_instance_id = 2;
+  string state = 3;                                       // DriverState-as-string in the record; kept as string
+  google.protobuf.Timestamp last_successful_read_utc = 4; // DateTime? — absent Timestamp encodes null
+  optional string last_error = 5;                         // nullable in the record
+  int32 error_count_5min = 6;
+  google.protobuf.Timestamp published_utc = 7;
+}
+
+// Mirrors ZB.MOM.WW.OtOpcUa.Commons.Messages.Drivers.DriverResilienceStatusChanged.
+message DriverResilienceStatus {
+  string driver_instance_id = 1;
+  string host_name = 2;
+  bool breaker_open = 3;
+  int32 consecutive_failures = 4;
+  int32 current_in_flight = 5;
+  google.protobuf.Timestamp last_breaker_open_utc = 6;    // DateTime? — absent Timestamp encodes null
+  google.protobuf.Timestamp last_sampled_utc = 7;
+  google.protobuf.Timestamp published_utc = 8;
+}
diff --git a/src/Core/ZB.MOM.WW.OtOpcUa.Commons/ZB.MOM.WW.OtOpcUa.Commons.csproj b/src/Core/ZB.MOM.WW.OtOpcUa.Commons/ZB.MOM.WW.OtOpcUa.Commons.csproj
index acad5d43..5e55544f 100644
--- a/src/Core/ZB.MOM.WW.OtOpcUa.Commons/ZB.MOM.WW.OtOpcUa.Commons.csproj
+++ b/src/Core/ZB.MOM.WW.OtOpcUa.Commons/ZB.MOM.WW.OtOpcUa.Commons.csproj
@@ -27,6 +27,7 @@
 
     <ItemGroup>
         <Protobuf Include="Protos\deployment_artifact.proto" GrpcServices="Both"/>
+        <Protobuf Include="Protos\telemetry.proto" GrpcServices="Both"/>
     </ItemGroup>
 
     <ItemGroup>
diff --git a/tests/Core/ZB.MOM.WW.OtOpcUa.Commons.Tests/TelemetryProtoContractTests.cs b/tests/Core/ZB.MOM.WW.OtOpcUa.Commons.Tests/TelemetryProtoContractTests.cs
new file mode 100644
index 00000000..855bb17a
--- /dev/null
+++ b/tests/Core/ZB.MOM.WW.OtOpcUa.Commons.Tests/TelemetryProtoContractTests.cs
@@ -0,0 +1,32 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Commons.Protos;
+using ZB.MOM.WW.OtOpcUa.Commons.Protos.Telemetry.V1;
+
+namespace ZB.MOM.WW.OtOpcUa.Commons.Tests;
+
+/// <summary>
+///     Contract-lock for the Phase 5 telemetry oneof. If a fifth variant is added to
+///     <c>telemetry.proto</c> without adding a matching entry to
+///     <see cref="TelemetryProtoContract.HandledCases"/>, this test goes red — the single guard that
+///     keeps the wire contract and the handled-case set from silently drifting apart.
+/// </summary>
+public class TelemetryProtoContractTests
+{
+    [Fact]
+    public void EveryOneofVariant_IsAccountedFor()
+    {
+        var variants = System.Enum.GetValues<TelemetryEvent.EventOneofCase>()
+            .Where(c => c != TelemetryEvent.EventOneofCase.None).ToArray();
+
+        variants.ShouldBe(TelemetryProtoContract.HandledCases, ignoreOrder: true);
+    }
+
+    [Fact]
+    public void The_service_base_and_client_types_generate()
+    {
+        // Referencing these types is the whole assertion — GrpcServices="Both" must emit both.
+        typeof(TelemetryStreamService.TelemetryStreamServiceBase).ShouldNotBeNull();
+        typeof(TelemetryStreamService.TelemetryStreamServiceClient).ShouldNotBeNull();
+    }
+}