diff --git a/src/ZB.MOM.WW.ScadaBridge.DataConnectionLayer/Adapters/IMxGatewayClient.cs b/src/ZB.MOM.WW.ScadaBridge.DataConnectionLayer/Adapters/IMxGatewayClient.cs
new file mode 100644
index 00000000..db9eefca
--- /dev/null
+++ b/src/ZB.MOM.WW.ScadaBridge.DataConnectionLayer/Adapters/IMxGatewayClient.cs
@@ -0,0 +1,79 @@
+using ZB.MOM.WW.ScadaBridge.Commons.Interfaces.Protocol;
+
+namespace ZB.MOM.WW.ScadaBridge.DataConnectionLayer.Adapters;
+
+/// <summary>Connection parameters resolved from the flat config dict.</summary>
+public record MxGatewayConnectionOptions(
+    string Endpoint, string ApiKey, string ClientName, int WriteUserId,
+    bool UseTls, string? CaFile, string? ServerName, int ReadTimeoutMs);
+
+/// <summary>One advised-tag value change pushed from the gateway event stream.</summary>
+public record MxValueUpdate(string TagPath, object? Value, QualityCode Quality, DateTimeOffset Timestamp);
+
+/// <summary>Per-tag read outcome.</summary>
+public record MxReadOutcome(string TagPath, bool Success, object? Value, QualityCode Quality, DateTimeOffset Timestamp, string? Error);
+
+/// <summary>Per-tag write outcome.</summary>
+public record MxWriteOutcome(string TagPath, bool Success, string? Error);
+
+/// <summary>One node in a Galaxy browse level.</summary>
+public record MxBrowseChild(string NodeId, string DisplayName, BrowseNodeClass NodeClass, bool HasChildren);
+
+/// <summary>
+/// Seam over the MxAccess Gateway .NET client + Galaxy repository client. Decouples
+/// <see cref="MxGatewayDataConnection"/> from the generated gRPC/protobuf types so the
+/// adapter is unit-testable with a fake. The real implementation lives in
+/// <c>RealMxGatewayClient</c>.
+/// </summary>
+public interface IMxGatewayClient : IAsyncDisposable
+{
+    /// <summary>Opens the gateway session and registers the client (Register → serverHandle held internally).</summary>
+    /// <param name="options">Resolved connection parameters.</param>
+    /// <param name="ct">Cancellation token.</param>
+    Task ConnectAsync(MxGatewayConnectionOptions options, CancellationToken ct = default);
+
+    /// <summary>Closes the session.</summary>
+    /// <param name="ct">Cancellation token.</param>
+    Task DisconnectAsync(CancellationToken ct = default);
+
+    /// <summary>AddItem + Advise; returns the gateway item handle (as a string subscription id).</summary>
+    /// <param name="tagPath">Tag address to subscribe to.</param>
+    /// <param name="ct">Cancellation token.</param>
+    Task<string> SubscribeAsync(string tagPath, CancellationToken ct = default);
+
+    /// <summary>UnAdvise + RemoveItem for a previously returned subscription id.</summary>
+    /// <param name="subscriptionId">Subscription id returned by <see cref="SubscribeAsync"/>.</param>
+    /// <param name="ct">Cancellation token.</param>
+    Task UnsubscribeAsync(string subscriptionId, CancellationToken ct = default);
+
+    /// <summary>Snapshot read of one or more tags (ReadBulk).</summary>
+    /// <param name="tagPaths">Tag addresses to read.</param>
+    /// <param name="ct">Cancellation token.</param>
+    Task<IReadOnlyList<MxReadOutcome>> ReadAsync(IReadOnlyList<string> tagPaths, CancellationToken ct = default);
+
+    /// <summary>Write one or more tag/value pairs (WriteBulk with the configured WriteUserId).</summary>
+    /// <param name="writes">Tag/value pairs to write.</param>
+    /// <param name="ct">Cancellation token.</param>
+    Task<IReadOnlyList<MxWriteOutcome>> WriteAsync(IReadOnlyList<(string TagPath, object? Value)> writes, CancellationToken ct = default);
+
+    /// <summary>One Galaxy browse level (BrowseChildren). <paramref name="parentNodeId"/> null → root.</summary>
+    /// <param name="parentNodeId">Parent node id (Galaxy contained path), or null for root.</param>
+    /// <param name="ct">Cancellation token.</param>
+    Task<(IReadOnlyList<MxBrowseChild> Children, bool Truncated)> BrowseChildrenAsync(string? parentNodeId, CancellationToken ct = default);
+
+    /// <summary>
+    /// Long-running event consumer. Invokes <paramref name="onUpdate"/> for each advised-tag
+    /// data change. Resumes from the last delivered worker sequence on reconnect. Completes
+    /// (or throws) when the stream ends — the adapter treats that as a disconnect.
+    /// </summary>
+    /// <param name="onUpdate">Callback invoked per advised-tag value change.</param>
+    /// <param name="ct">Cancellation token; ends the loop when cancelled.</param>
+    Task RunEventLoopAsync(Action<MxValueUpdate> onUpdate, CancellationToken ct = default);
+}
+
+/// <summary>Builds <see cref="IMxGatewayClient"/> instances.</summary>
+public interface IMxGatewayClientFactory
+{
+    /// <summary>Creates a new, unconnected client instance.</summary>
+    IMxGatewayClient Create();
+}
diff --git a/src/ZB.MOM.WW.ScadaBridge.DataConnectionLayer/MxGatewayGlobalOptions.cs b/src/ZB.MOM.WW.ScadaBridge.DataConnectionLayer/MxGatewayGlobalOptions.cs
new file mode 100644
index 00000000..190f1017
--- /dev/null
+++ b/src/ZB.MOM.WW.ScadaBridge.DataConnectionLayer/MxGatewayGlobalOptions.cs
@@ -0,0 +1,11 @@
+namespace ZB.MOM.WW.ScadaBridge.DataConnectionLayer;
+
+/// <summary>
+/// Deployment-wide MxGateway defaults, bound from the "MxGateway" section of
+/// appsettings.json. Per-endpoint behavior lives on MxGatewayEndpointConfig.
+/// </summary>
+public class MxGatewayGlobalOptions
+{
+    /// <summary>Prefix used to derive a per-connection client registration name when the connection's ClientName is blank.</summary>
+    public string ClientNamePrefix { get; set; } = "scadabridge";
+}