diff --git a/src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/DriverTypeNames.cs b/src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/DriverTypeNames.cs
index d4ba0417..6e65b231 100644
--- a/src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/DriverTypeNames.cs
+++ b/src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/DriverTypeNames.cs
@@ -53,6 +53,9 @@ public static class DriverTypeNames
     /// <summary>Calculation pseudo-driver — tags computed by C# scripts over other tags' live values.</summary>
     public const string Calculation = "Calculation";
 
+    /// <summary>MQTT / Sparkplug B broker-subscription driver.</summary>
+    public const string Mqtt = "Mqtt";
+
     /// <summary>
     ///     Every driver-type string declared above, for callers that need to enumerate
     ///     the full set (e.g. validation of an authored <c>DriverType</c>).
@@ -68,5 +71,6 @@ public static class DriverTypeNames
         OpcUaClient,
         Galaxy,
         Calculation,
+        Mqtt,
     ];
 }
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Browser/MqttDriverBrowser.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Browser/MqttDriverBrowser.cs
index ce2f3366..42c049d6 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Browser/MqttDriverBrowser.cs
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Browser/MqttDriverBrowser.cs
@@ -1,11 +1,11 @@
 using System.Buffers;
 using System.Text.Json;
-using System.Text.Json.Serialization;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Abstractions;
 using MQTTnet;
 using MQTTnet.Protocol;
 using ZB.MOM.WW.OtOpcUa.Commons.Browsing;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
 
 namespace ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Browser;
 
@@ -39,19 +39,6 @@ public sealed class MqttDriverBrowser : IDriverBrowser
     /// <summary>Marks the transient browse identity in the broker's client-id/session logs.</summary>
     internal const string BrowseClientIdPrefix = "-browse-";
 
-    /// <summary>
-    ///     Matches the runtime driver factory's parsing so a given DriverConfig JSON means the same
-    ///     thing to the browser as it does to the deployed driver. <c>JsonStringEnumConverter</c> lets
-    ///     <c>mode</c> / <c>protocolVersion</c> be authored as their string names — the natural form
-    ///     for AdminUI-emitted JSON — while still accepting numeric ordinals.
-    /// </summary>
-    private static readonly JsonSerializerOptions JsonOpts = new()
-    {
-        UnmappedMemberHandling = JsonUnmappedMemberHandling.Skip,
-        PropertyNameCaseInsensitive = true,
-        Converters = { new JsonStringEnumConverter() },
-    };
-
     private readonly ILogger<MqttDriverBrowser> _logger;
 
     /// <summary>
@@ -64,10 +51,7 @@ public sealed class MqttDriverBrowser : IDriverBrowser
         _logger = logger ?? NullLogger<MqttDriverBrowser>.Instance;
 
     /// <inheritdoc />
-    // Literal rather than a constant: DriverTypeNames.Mqtt does not exist yet — Task 9 adds it, and
-    // owns that file. The string must stay EXACTLY "Mqtt": a DriverType string that drifts from the
-    // persisted one silently breaks driver dispatch (the repo's ModbusTcp/Modbus incident).
-    public string DriverType => "Mqtt";
+    public string DriverType => DriverTypeNames.Mqtt;
 
     /// <inheritdoc />
     /// <remarks>
@@ -77,7 +61,11 @@ public sealed class MqttDriverBrowser : IDriverBrowser
     /// </remarks>
     public async Task<IBrowseSession> OpenAsync(string configJson, CancellationToken cancellationToken)
     {
-        var opts = JsonSerializer.Deserialize<MqttDriverOptions>(configJson, JsonOpts)
+        // MqttJson.Options — the ONE shared instance across factory / probe / driver / browser
+        // (see its remarks). Parsing the same DriverConfig blob through a second, divergent
+        // JsonSerializerOptions is this repo's documented systemic enum bug: the picker would accept
+        // a `mode` / `protocolVersion` spelling the deployed driver rejects, or vice versa.
+        var opts = JsonSerializer.Deserialize<MqttDriverOptions>(configJson, MqttJson.Options)
             ?? throw new InvalidOperationException("Mqtt options deserialized to null.");
 
         if (opts.Mode == MqttMode.SparkplugB)
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Contracts/MqttJson.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Contracts/MqttJson.cs
new file mode 100644
index 00000000..944f653d
--- /dev/null
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Contracts/MqttJson.cs
@@ -0,0 +1,53 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Mqtt;
+
+/// <summary>
+///     The <b>single</b> <see cref="JsonSerializerOptions"/> instance every MQTT driver-config seam
+///     parses <see cref="MqttDriverOptions"/> through — the runtime factory
+///     (<c>MqttDriverFactoryExtensions</c>), the Test-connect probe (<c>MqttDriverProbe</c>), the
+///     driver's own <c>ReinitializeAsync</c> re-parse, and the address-picker browser
+///     (<c>MqttDriverBrowser</c>).
+/// </summary>
+/// <remarks>
+///     <para>
+///         <b>Why one instance, and why here.</b> Divergent per-seam options are this repo's
+///         documented systemic enum bug: an AdminUI-authored config with an enum-valued field is
+///         accepted by the seam that carries a <see cref="JsonStringEnumConverter"/> and faults the
+///         one that does not, so "Test connect" goes green and the deployed driver dies. Two other
+///         drivers already carry a copy per seam. Rather than repeat that, this driver keeps exactly
+///         one instance.
+///     </para>
+///     <para>
+///         It lives in <c>.Contracts</c> — the assembly that owns <see cref="MqttDriverOptions"/> and
+///         the three enums the converter exists for — rather than in the factory or the probe,
+///         because <c>.Contracts</c> is the <i>only</i> assembly all four consumers already reference.
+///         In particular the browser lives in its own assembly and reaches the runtime <c>.Driver</c>
+///         project only through a deliberate, documented layering exception that is scheduled to be
+///         removed (see the <c>ProjectReference</c> comment in the browser's csproj); anchoring the
+///         options in <c>.Driver</c> would resurrect the duplicate the day that reference goes away.
+///     </para>
+///     <para>
+///         <b>Not a general-purpose JSON policy.</b> <c>UnmappedMemberHandling.Skip</c> means an
+///         unknown key is ignored rather than rejected — deliberate, so a config blob authored
+///         against a newer driver still binds — and <c>PropertyNameCaseInsensitive</c> accepts both
+///         the camelCase the AdminUI emits and the PascalCase a hand-edited blob may carry. A
+///         <see cref="JsonSerializerOptions"/> becomes read-only on first use, so this instance is
+///         safe to share across threads and must never be mutated after startup.
+///     </para>
+/// </remarks>
+public static class MqttJson
+{
+    /// <summary>
+    ///     The shared options. Enum-valued knobs (<see cref="MqttMode"/>,
+    ///     <see cref="MqttProtocolVersion"/>, <see cref="MqttPayloadFormat"/>) round-trip by
+    ///     <b>name</b>; numeric ordinals still bind, so an older blob is not broken by this.
+    /// </summary>
+    public static readonly JsonSerializerOptions Options = new()
+    {
+        PropertyNameCaseInsensitive = true,
+        UnmappedMemberHandling = JsonUnmappedMemberHandling.Skip,
+        Converters = { new JsonStringEnumConverter() },
+    };
+}
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt/MqttDriver.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt/MqttDriver.cs
index 5481f1cd..b7db7439 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt/MqttDriver.cs
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt/MqttDriver.cs
@@ -123,11 +123,7 @@ public sealed class MqttDriver
     public string DriverInstanceId => _driverInstanceId;
 
     /// <inheritdoc />
-    // Literal rather than a constant: DriverTypeNames.Mqtt does not exist yet — Task 9 adds it and
-    // owns that file. The string must stay EXACTLY "Mqtt" and match MqttDriverProbe.DriverType: a
-    // DriverType that drifts from the persisted one silently breaks dispatch (the ModbusTcp/Modbus
-    // incident).
-    public string DriverType => "Mqtt";
+    public string DriverType => DriverTypeNames.Mqtt;
 
     /// <summary>
     ///     The ingest path this driver composes. Internal: the P2 Sparkplug handler feeds the same
@@ -513,10 +509,11 @@ public sealed class MqttDriver
 
         try
         {
-            // The probe's shared instance, deliberately: enums must round-trip by NAME. A second,
-            // divergent JsonSerializerOptions is this repo's documented systemic enum bug, where an
-            // AdminUI-authored config with a numeric enum field faults the driver.
-            return JsonSerializer.Deserialize<MqttDriverOptions>(driverConfigJson, MqttDriverProbe.JsonOpts);
+            // MqttJson.Options — the ONE shared instance (factory / probe / this / browser),
+            // deliberately: enums must round-trip by NAME. A second, divergent
+            // JsonSerializerOptions is this repo's documented systemic enum bug, where an
+            // AdminUI-authored config with a string enum field faults the driver.
+            return JsonSerializer.Deserialize<MqttDriverOptions>(driverConfigJson, MqttJson.Options);
         }
         catch (JsonException ex)
         {
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt/MqttDriverFactoryExtensions.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt/MqttDriverFactoryExtensions.cs
new file mode 100644
index 00000000..dc6d9bea
--- /dev/null
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt/MqttDriverFactoryExtensions.cs
@@ -0,0 +1,84 @@
+using System.Text.Json;
+using Microsoft.Extensions.Logging;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.Hosting;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Mqtt;
+
+/// <summary>
+///     Registers the MQTT / Sparkplug B driver with the <see cref="DriverFactoryRegistry"/>. The
+///     Host's <c>DriverFactoryBootstrap</c> calls <see cref="Register"/> once at startup; the
+///     driver-instance bootstrapper then materialises <c>DriverInstance</c> rows of type
+///     <see cref="DriverTypeNames.Mqtt"/> into live <see cref="MqttDriver"/> instances.
+/// </summary>
+/// <remarks>
+///     <para>
+///         <b>Direct deserialization, no intermediate DTO.</b> The <c>DriverConfig</c> blob binds
+///         straight onto <see cref="MqttDriverOptions"/> — the same shape
+///         <see cref="MqttDriverProbe"/>, <c>MqttDriverBrowser</c> and
+///         <see cref="MqttDriver.ReinitializeAsync"/> already bind, and the shape the options record
+///         was designed for (every knob carries its own default, and <c>rawTags</c> is a plain
+///         <see cref="RawTagEntry"/> list needing no translation). Mirrors
+///         <c>OpcUaClientDriverFactoryExtensions</c>. <c>ModbusDriverFactoryExtensions</c>' separate
+///         DTO exists to service a legacy nullable-everything blob plus string→enum parsing this
+///         driver does with a converter instead; copying it here would add a <i>fourth</i> parse
+///         shape for one config, which is precisely the divergence
+///         <see cref="MqttJson.Options"/> exists to prevent.
+///     </para>
+///     <para>
+///         <b>Connection-free.</b> <see cref="CreateInstance"/> parses and constructs only — the
+///         <see cref="MqttDriver"/> constructor touches no network, and the registry contract
+///         forbids the factory from calling <c>InitializeAsync</c> itself (the driver host owns the
+///         retry semantics).
+///     </para>
+/// </remarks>
+public static class MqttDriverFactoryExtensions
+{
+    /// <summary>
+    ///     Driver type name — matches <c>DriverInstance.DriverType</c> values. Sourced from
+    ///     <see cref="DriverTypeNames.Mqtt"/> so the registration key can never drift from the
+    ///     constant the dispatch maps, the probe and the browser reference.
+    /// </summary>
+    public const string DriverTypeName = DriverTypeNames.Mqtt;
+
+    /// <summary>
+    ///     Register the MQTT factory with the driver registry. The optional
+    ///     <paramref name="loggerFactory"/> is captured at registration time and used to construct an
+    ///     <see cref="ILogger{MqttDriver}"/> per driver instance — without it the driver runs with no
+    ///     logger (standalone/test callers stay unchanged).
+    /// </summary>
+    /// <param name="registry">The driver factory registry to register with.</param>
+    /// <param name="loggerFactory">Optional logger factory used to create per-instance loggers.</param>
+    public static void Register(DriverFactoryRegistry registry, ILoggerFactory? loggerFactory = null)
+    {
+        ArgumentNullException.ThrowIfNull(registry);
+        registry.Register(DriverTypeName, (id, json) => CreateInstance(id, json, loggerFactory));
+    }
+
+    /// <summary>Public for the Server-side bootstrapper + test consumers.</summary>
+    /// <param name="driverInstanceId">Stable logical id of the driver instance.</param>
+    /// <param name="driverConfigJson">The <c>DriverConfig</c> JSON blob for the instance.</param>
+    /// <param name="loggerFactory">Optional logger factory for the per-instance logger.</param>
+    /// <returns>A configured, not-yet-connected <see cref="MqttDriver"/>.</returns>
+    /// <exception cref="ArgumentException">
+    ///     <paramref name="driverInstanceId"/> or <paramref name="driverConfigJson"/> is blank.
+    /// </exception>
+    /// <exception cref="InvalidOperationException">The config blob deserialised to <c>null</c>.</exception>
+    /// <exception cref="JsonException">The config blob is not valid JSON for the options shape.</exception>
+    public static MqttDriver CreateInstance(
+        string driverInstanceId,
+        string driverConfigJson,
+        ILoggerFactory? loggerFactory = null)
+    {
+        ArgumentException.ThrowIfNullOrWhiteSpace(driverInstanceId);
+        ArgumentException.ThrowIfNullOrWhiteSpace(driverConfigJson);
+
+        // MqttJson.Options — the one shared instance (see its remarks). A local copy here is the
+        // repo's documented systemic enum bug in the making.
+        var options = JsonSerializer.Deserialize<MqttDriverOptions>(driverConfigJson, MqttJson.Options)
+            ?? throw new InvalidOperationException(
+                $"MQTT driver config for '{driverInstanceId}' deserialised to null");
+
+        return new MqttDriver(options, driverInstanceId, loggerFactory?.CreateLogger<MqttDriver>());
+    }
+}
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt/MqttDriverProbe.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt/MqttDriverProbe.cs
index ce8a71cc..4a6e973a 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt/MqttDriverProbe.cs
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt/MqttDriverProbe.cs
@@ -2,7 +2,6 @@ using System.Diagnostics;
 using System.Net.Sockets;
 using System.Security.Authentication;
 using System.Text.Json;
-using System.Text.Json.Serialization;
 using Microsoft.Extensions.Logging.Abstractions;
 using MQTTnet;
 using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
@@ -55,26 +54,8 @@ public sealed class MqttDriverProbe : IDriverProbe
     /// </summary>
     internal const string ProbeClientIdPrefix = "-probe-";
 
-    /// <summary>
-    ///     Shared JSON options for every MQTT config-parsing seam in this driver: enums
-    ///     (<see cref="MqttMode"/>, <see cref="MqttPayloadFormat"/>, <c>protocolVersion</c>)
-    ///     round-trip by <b>name</b>, never ordinal — the repo's documented enum-serialization
-    ///     trap (AdminUI-authored configs with numeric enum fields fault the driver). Task 9's
-    ///     <c>MqttDriverFactoryExtensions</c> is expected to converge on this same instance
-    ///     rather than defining its own.
-    /// </summary>
-    internal static readonly JsonSerializerOptions JsonOpts = new()
-    {
-        PropertyNameCaseInsensitive = true,
-        UnmappedMemberHandling = JsonUnmappedMemberHandling.Skip,
-        Converters = { new JsonStringEnumConverter() },
-    };
-
     /// <inheritdoc />
-    // Literal rather than a constant: DriverTypeNames.Mqtt does not exist yet — Task 9 adds it, and
-    // owns that file. The string must stay EXACTLY "Mqtt": a DriverType string that drifts from the
-    // persisted one silently breaks driver dispatch (the repo's ModbusTcp/Modbus incident).
-    public string DriverType => "Mqtt";
+    public string DriverType => DriverTypeNames.Mqtt;
 
     /// <inheritdoc />
     public async Task<DriverProbeResult> ProbeAsync(string configJson, TimeSpan timeout, CancellationToken ct)
@@ -82,7 +63,10 @@ public sealed class MqttDriverProbe : IDriverProbe
         MqttDriverOptions? options;
         try
         {
-            options = JsonSerializer.Deserialize<MqttDriverOptions>(configJson, JsonOpts);
+            // MqttJson.Options — the one shared instance across factory / probe / driver / browser
+            // (see its remarks): enums must round-trip by NAME or an AdminUI-authored config that
+            // Test-connect accepts would fault the deployed driver.
+            options = JsonSerializer.Deserialize<MqttDriverOptions>(configJson, MqttJson.Options);
         }
         catch (Exception ex)
         {
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.Host/Drivers/DriverFactoryBootstrap.cs b/src/Server/ZB.MOM.WW.OtOpcUa.Host/Drivers/DriverFactoryBootstrap.cs
index 71b5d0b7..fe19a128 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.Host/Drivers/DriverFactoryBootstrap.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.Host/Drivers/DriverFactoryBootstrap.cs
@@ -18,6 +18,7 @@ using FocasProbe     = Driver.FOCAS.FocasDriverProbe;
 using OpcUaProbe     = Driver.OpcUaClient.OpcUaClientDriverProbe;
 using GalaxyProbe    = Driver.Galaxy.GalaxyDriverProbe;
 using CalculationProbe = Driver.Calculation.CalculationDriverProbe;
+using MqttProbe      = Driver.Mqtt.MqttDriverProbe;
 
 /// <summary>
 ///     Wires every cross-platform driver assembly's <c>Register(registry, loggerFactory)</c>
@@ -122,6 +123,7 @@ public static class DriverFactoryBootstrap
         services.TryAddEnumerable(ServiceDescriptor.Singleton<IDriverProbe, OpcUaProbe>());
         services.TryAddEnumerable(ServiceDescriptor.Singleton<IDriverProbe, GalaxyProbe>());
         services.TryAddEnumerable(ServiceDescriptor.Singleton<IDriverProbe, CalculationProbe>());
+        services.TryAddEnumerable(ServiceDescriptor.Singleton<IDriverProbe, MqttProbe>());
 
         return services;
     }
@@ -144,6 +146,7 @@ public static class DriverFactoryBootstrap
         Driver.FOCAS.FocasDriverFactoryExtensions.Register(registry);
         Driver.Galaxy.GalaxyDriverFactoryExtensions.Register(registry, secretResolver, loggerFactory);
         Driver.Modbus.ModbusDriverFactoryExtensions.Register(registry, loggerFactory);
+        Driver.Mqtt.MqttDriverFactoryExtensions.Register(registry, loggerFactory);
         Driver.OpcUaClient.OpcUaClientDriverFactoryExtensions.Register(registry, loggerFactory, secretResolver);
         Driver.S7.S7DriverFactoryExtensions.Register(registry);
         Driver.TwinCAT.TwinCATDriverFactoryExtensions.Register(registry);
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.Host/ZB.MOM.WW.OtOpcUa.Host.csproj b/src/Server/ZB.MOM.WW.OtOpcUa.Host/ZB.MOM.WW.OtOpcUa.Host.csproj
index dd7fbd9a..ebcea6c5 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.Host/ZB.MOM.WW.OtOpcUa.Host.csproj
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.Host/ZB.MOM.WW.OtOpcUa.Host.csproj
@@ -74,6 +74,7 @@
         <ProjectReference Include="..\..\Drivers\ZB.MOM.WW.OtOpcUa.Driver.Galaxy\ZB.MOM.WW.OtOpcUa.Driver.Galaxy.csproj"/>
         <ProjectReference Include="..\..\Drivers\ZB.MOM.WW.OtOpcUa.Driver.Historian.Gateway\ZB.MOM.WW.OtOpcUa.Driver.Historian.Gateway.csproj"/>
         <ProjectReference Include="..\..\Drivers\ZB.MOM.WW.OtOpcUa.Driver.Modbus\ZB.MOM.WW.OtOpcUa.Driver.Modbus.csproj"/>
+        <ProjectReference Include="..\..\Drivers\ZB.MOM.WW.OtOpcUa.Driver.Mqtt\ZB.MOM.WW.OtOpcUa.Driver.Mqtt.csproj"/>
         <ProjectReference Include="..\..\Drivers\ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient\ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.csproj"/>
         <ProjectReference Include="..\..\Drivers\ZB.MOM.WW.OtOpcUa.Driver.S7\ZB.MOM.WW.OtOpcUa.Driver.S7.csproj"/>
         <ProjectReference Include="..\..\Drivers\ZB.MOM.WW.OtOpcUa.Driver.TwinCAT\ZB.MOM.WW.OtOpcUa.Driver.TwinCAT.csproj"/>
diff --git a/tests/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions.Tests/ZB.MOM.WW.OtOpcUa.Core.Abstractions.Tests.csproj b/tests/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions.Tests/ZB.MOM.WW.OtOpcUa.Core.Abstractions.Tests.csproj
index b89bfe91..1e32d03c 100644
--- a/tests/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions.Tests/ZB.MOM.WW.OtOpcUa.Core.Abstractions.Tests.csproj
+++ b/tests/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions.Tests/ZB.MOM.WW.OtOpcUa.Core.Abstractions.Tests.csproj
@@ -21,11 +21,12 @@
 
     <ItemGroup>
         <ProjectReference Include="..\..\..\src\Core\ZB.MOM.WW.OtOpcUa.Core.Abstractions\ZB.MOM.WW.OtOpcUa.Core.Abstractions.csproj"/>
-        <!-- Core hosts DriverFactoryRegistry; the eight driver assemblies each ship the
+        <!-- Core hosts DriverFactoryRegistry; the driver assemblies below each ship the
              *DriverFactoryExtensions.Register entry point the guard test drives to build the
              authoritative registered-factory set (mirrors the Host's DriverFactoryBootstrap). -->
         <ProjectReference Include="..\..\..\src\Core\ZB.MOM.WW.OtOpcUa.Core\ZB.MOM.WW.OtOpcUa.Core.csproj"/>
         <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.Modbus\ZB.MOM.WW.OtOpcUa.Driver.Modbus.csproj"/>
+        <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.Mqtt\ZB.MOM.WW.OtOpcUa.Driver.Mqtt.csproj"/>
         <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.S7\ZB.MOM.WW.OtOpcUa.Driver.S7.csproj"/>
         <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.AbCip\ZB.MOM.WW.OtOpcUa.Driver.AbCip.csproj"/>
         <ProjectReference Include="..\..\..\src\Drivers\ZB.MOM.WW.OtOpcUa.Driver.AbLegacy\ZB.MOM.WW.OtOpcUa.Driver.AbLegacy.csproj"/>
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Tests/MqttDriverFactoryExtensionsTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Tests/MqttDriverFactoryExtensionsTests.cs
new file mode 100644
index 00000000..ad4e2191
--- /dev/null
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Tests/MqttDriverFactoryExtensionsTests.cs
@@ -0,0 +1,151 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Core.Hosting;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Tests;
+
+/// <summary>
+///     Tests for <see cref="MqttDriverFactoryExtensions"/> — the seam that turns a persisted
+///     <c>DriverInstance.DriverConfig</c> blob into a live <see cref="MqttDriver"/>. Mirrors
+///     <c>OpcUaClientDriverFactoryExtensions</c>' shape (direct deserialization into the options
+///     record, no intermediate DTO).
+/// </summary>
+[Trait("Category", "Unit")]
+public sealed class MqttDriverFactoryExtensionsTests
+{
+    [Fact]
+    public void Register_ThenCreate_BuildsMqttDriver()
+    {
+        var registry = new DriverFactoryRegistry();
+        MqttDriverFactoryExtensions.Register(registry);
+
+        var factory = registry.TryGet(MqttDriverFactoryExtensions.DriverTypeName);
+        factory.ShouldNotBeNull();
+
+        var driver = factory("d1", """{"host":"h","port":1883,"mode":"Plain"}""");
+
+        driver.ShouldBeOfType<MqttDriver>();
+    }
+
+    /// <summary>
+    ///     The factory's registration key and the canonical constant must be the same string. A
+    ///     drift here is invisible at compile time and silently breaks dispatch — the repo's
+    ///     <c>ModbusTcp</c>/<c>Modbus</c> incident.
+    /// </summary>
+    [Fact]
+    public void DriverTypeName_MatchesConstant()
+        => MqttDriverFactoryExtensions.DriverTypeName.ShouldBe(DriverTypeNames.Mqtt);
+
+    /// <summary>
+    ///     Third independent pin on the literal itself: both the constant and the factory name could
+    ///     be renamed together and still agree with each other while disagreeing with every persisted
+    ///     <c>DriverInstance.DriverType</c> row.
+    /// </summary>
+    [Fact]
+    public void DriverTypeName_IsExactlyMqtt()
+    {
+        MqttDriverFactoryExtensions.DriverTypeName.ShouldBe("Mqtt");
+        DriverTypeNames.Mqtt.ShouldBe("Mqtt");
+        DriverTypeNames.All.ShouldContain("Mqtt");
+    }
+
+    /// <summary>
+    ///     <c>rawTags</c> is the ONLY source of the driver's discoverable node set (plain MQTT has no
+    ///     browsable address space), so a factory that parsed everything else correctly but dropped
+    ///     this array would produce a driver that connects, subscribes to nothing and materializes
+    ///     nothing — green everywhere, dark in production.
+    /// </summary>
+    [Fact]
+    public async Task CreateInstance_CarriesRawTagsThroughToDiscovery()
+    {
+        const string tagConfig = """{"topic":"f/t","payloadFormat":"Raw","dataType":"String"}""";
+        var json = JsonSerializer.Serialize(new
+        {
+            host = "h",
+            port = 1883,
+            mode = "Plain",
+            rawTags = new[]
+            {
+                new { rawPath = "Plant/Mqtt/dev1/Temp", tagConfig, writeIdempotent = false },
+            },
+        });
+
+        var driver = MqttDriverFactoryExtensions.CreateInstance("d1", json);
+
+        var builder = new RecordingBuilder();
+        await driver.DiscoverAsync(builder, CancellationToken.None);
+
+        builder.VariableFullNames.ShouldBe(["Plant/Mqtt/dev1/Temp"]);
+    }
+
+    /// <summary>
+    ///     Enum-valued knobs must bind from their string NAMES — the repo's documented systemic
+    ///     enum-serialization bug is an AdminUI-authored config whose enum field one seam can read
+    ///     and another cannot. Removing <see cref="JsonStringEnumConverter"/> from
+    ///     <see cref="MqttJson.Options"/> makes this throw.
+    /// </summary>
+    [Fact]
+    public void CreateInstance_EnumsAuthoredAsNames_Bind()
+    {
+        const string json = """
+            {"host":"h","port":8883,"mode":"SparkplugB","protocolVersion":"V311",
+             "sparkplug":{"groupId":"Plant1","hostId":"h1"}}
+            """;
+
+        var driver = MqttDriverFactoryExtensions.CreateInstance("d1", json);
+
+        driver.ShouldBeOfType<MqttDriver>();
+    }
+
+    /// <summary>
+    ///     Direct pin on the single shared instance: the enum converter is what the test above
+    ///     exercises behaviourally, and this asserts it structurally so a reader can see the one
+    ///     instance every MQTT config seam parses through.
+    /// </summary>
+    [Fact]
+    public void SharedJsonOptions_CarryTheStringEnumConverter()
+        => MqttJson.Options.Converters.ShouldContain(c => c is JsonStringEnumConverter);
+
+    [Fact]
+    public void CreateInstance_BlankConfig_Throws()
+        => Should.Throw<ArgumentException>(() => MqttDriverFactoryExtensions.CreateInstance("d1", "  "));
+
+    [Fact]
+    public void CreateInstance_JsonNullLiteral_ThrowsInvalidOperation()
+        => Should.Throw<InvalidOperationException>(() => MqttDriverFactoryExtensions.CreateInstance("d1", "null"));
+
+    /// <summary>
+    ///     Minimal discovery recorder — local to this suite because the driver test project does not
+    ///     reference <c>Commons</c>, where the runtime's capturing builder lives (same reason
+    ///     <c>MqttDriverDiscoveryTests</c> carries its own).
+    /// </summary>
+    private sealed class RecordingBuilder : IAddressSpaceBuilder
+    {
+        public List<string> VariableFullNames { get; } = [];
+
+        public IAddressSpaceBuilder Folder(string browseName, string displayName) => this;
+
+        public IVariableHandle Variable(string browseName, string displayName, DriverAttributeInfo attributeInfo)
+        {
+            VariableFullNames.Add(attributeInfo.FullName);
+            return new Handle(attributeInfo.FullName);
+        }
+
+        public void AddProperty(string browseName, DriverDataType dataType, object? value) { }
+
+        private sealed class Handle(string fullRef) : IVariableHandle
+        {
+            public string FullReference => fullRef;
+
+            public IAlarmConditionSink MarkAsAlarmCondition(AlarmConditionInfo info) => new NullSink();
+        }
+
+        private sealed class NullSink : IAlarmConditionSink
+        {
+            public void OnTransition(AlarmEventArgs args) { }
+        }
+    }
+}
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Tests/MqttDriverOptionsTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Tests/MqttDriverOptionsTests.cs
index ce7e2c3c..d6fc1cb9 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Tests/MqttDriverOptionsTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Tests/MqttDriverOptionsTests.cs
@@ -1,5 +1,4 @@
 using System.Text.Json;
-using System.Text.Json.Serialization;
 using Shouldly;
 using Xunit;
 using ZB.MOM.WW.OtOpcUa.Driver.Mqtt;
@@ -8,12 +7,12 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Tests;
 
 public sealed class MqttDriverOptionsTests
 {
-    private static readonly JsonSerializerOptions J = new()
-    {
-        PropertyNameCaseInsensitive = true,
-        UnmappedMemberHandling = JsonUnmappedMemberHandling.Skip,
-        Converters = { new JsonStringEnumConverter() },
-    };
+    /// <summary>
+    ///     The production instance, not a look-alike copy. A local clone would keep passing after
+    ///     <see cref="MqttJson.Options"/> lost its <c>JsonStringEnumConverter</c> — testing the copy
+    ///     instead of the thing every seam actually parses through.
+    /// </summary>
+    private static readonly JsonSerializerOptions J = MqttJson.Options;
 
     [Fact]
     public void Deserialize_SparkplugConfig_ReadsModeAndSubObject()
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Tests/MqttDriverProbeTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Tests/MqttDriverProbeTests.cs
index 14c70eab..5f3e1b5e 100644
--- a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Tests/MqttDriverProbeTests.cs
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Mqtt.Tests/MqttDriverProbeTests.cs
@@ -161,10 +161,20 @@ public sealed class MqttDriverProbeTests
         r.Message.ShouldNotContain(secret);
     }
 
-    /// <summary>Enum fields (protocolVersion) must round-trip by name, per the repo's documented
-    /// enum-serialization trap — a numeric-only seam faults AdminUI-authored configs.</summary>
+    /// <summary>
+    ///     Enum fields (protocolVersion) must round-trip by name, per the repo's documented
+    ///     enum-serialization trap — a numeric-only seam faults AdminUI-authored configs.
+    ///     <para>
+    ///         <b>The assertions are the whole point.</b> "Ok is false with a non-empty message" is
+    ///         ALSO what a JSON-parse failure produces, so asserting only that would stay green if
+    ///         <c>JsonStringEnumConverter</c> were ever dropped from <see cref="MqttJson.Options"/>
+    ///         — i.e. the exact regression this test exists to catch. So it asserts the probe got
+    ///         PAST the parse (message is not the <c>"Config JSON is invalid"</c> shape) and reached
+    ///         the network (the message names the target endpoint).
+    ///     </para>
+    /// </summary>
     [Fact]
-    public async Task ProbeAsync_EnumAsName_DoesNotThrow()
+    public async Task ProbeAsync_EnumAsName_ParsesAndReachesTheNetwork()
     {
         var listener = StartListener();
         var port = ListenerPort(listener);
@@ -178,5 +188,14 @@ public sealed class MqttDriverProbeTests
 
         r.Ok.ShouldBeFalse();
         r.Message.ShouldNotBeNullOrEmpty();
+        r.Message.ShouldNotStartWith(
+            "Config JSON is invalid",
+            Case.Insensitive,
+            "the probe never parsed the config — 'V500' was rejected, so the shared JSON options " +
+            "lost their JsonStringEnumConverter");
+        r.Message.ShouldNotStartWith("Config JSON deserialized to null");
+        r.Message.ShouldNotStartWith("Config has no host/port");
+        // A network-level marker: the probe got as far as dialling the (closed) loopback port.
+        r.Message.ShouldContain($"127.0.0.1:{port}");
     }
 }