diff --git a/src/ClaudeDo.Installer/Core/ConfigModels.cs b/src/ClaudeDo.Installer/Core/ConfigModels.cs
index 462a0355..664b6299 100644
--- a/src/ClaudeDo.Installer/Core/ConfigModels.cs
+++ b/src/ClaudeDo.Installer/Core/ConfigModels.cs
@@ -52,6 +52,9 @@ public sealed class InstallerWorkerConfig
     [JsonPropertyName("claude_bin")]
     public string ClaudeBin { get; set; } = "claude";
 
+    [JsonPropertyName("external_mcp_port")]
+    public int ExternalMcpPort { get; set; } = 47_822;
+
     private static readonly JsonSerializerOptions ReadOpts = new()
     {
         ReadCommentHandling = JsonCommentHandling.Skip,
diff --git a/src/ClaudeDo.Installer/Steps/RegisterMcpStep.cs b/src/ClaudeDo.Installer/Steps/RegisterMcpStep.cs
index cb7817d6..b3f4cc25 100644
--- a/src/ClaudeDo.Installer/Steps/RegisterMcpStep.cs
+++ b/src/ClaudeDo.Installer/Steps/RegisterMcpStep.cs
@@ -5,9 +5,23 @@ namespace ClaudeDo.Installer.Steps;
 public sealed class RegisterMcpStep : IInstallStep
 {
     private const string ServerName = "claudedo";
+    private readonly Func<InstallerWorkerConfig> _loadWorkerConfig;
+
+    public RegisterMcpStep(Func<InstallerWorkerConfig>? loadWorkerConfig = null)
+    {
+        _loadWorkerConfig = loadWorkerConfig ?? InstallerWorkerConfig.Load;
+    }
 
     public string Name => "Register MCP with Claude";
 
+    // Resolves the URL from the persisted worker.config.json rather than ctx.ExternalMcpPort:
+    // an Update run never repopulates ctx from the existing installation, so ctx would still
+    // hold the wizard default (47822) even when the installed config has a different port.
+    // Returns null when the port is 0 — WorkerConfig treats that as "external listener off",
+    // so registering a URL against it would just point Claude at nothing.
+    public static string? ResolveUrl(InstallerWorkerConfig cfg) =>
+        cfg.ExternalMcpPort == 0 ? null : $"http://127.0.0.1:{cfg.ExternalMcpPort}/mcp";
+
     public async Task<StepResult> ExecuteAsync(InstallContext ctx, IProgress<string> progress, CancellationToken ct)
     {
         if (!ctx.RegisterMcpWithClaude)
@@ -16,7 +30,12 @@ public sealed class RegisterMcpStep : IInstallStep
             return StepResult.Ok();
         }
 
-        var url = $"http://127.0.0.1:{ctx.ExternalMcpPort}/mcp";
+        var url = ResolveUrl(_loadWorkerConfig());
+        if (url is null)
+        {
+            progress.Report("Skipped (external_mcp_port is 0 — the external MCP listener is disabled).");
+            return StepResult.Ok();
+        }
 
         // Drop any prior registration first so a re-run (e.g. update, changed port)
         // overwrites cleanly instead of erroring on a duplicate name.
diff --git a/tests/ClaudeDo.Installer.Tests/RegisterMcpStepTests.cs b/tests/ClaudeDo.Installer.Tests/RegisterMcpStepTests.cs
new file mode 100644
index 00000000..cfccbf88
--- /dev/null
+++ b/tests/ClaudeDo.Installer.Tests/RegisterMcpStepTests.cs
@@ -0,0 +1,65 @@
+using ClaudeDo.Installer.Core;
+using ClaudeDo.Installer.Steps;
+
+namespace ClaudeDo.Installer.Tests;
+
+public sealed class RegisterMcpStepTests
+{
+    // Progress<T> posts to the SynchronizationContext (or the ThreadPool) asynchronously,
+    // so asserting on captured messages right after an await needs a synchronous reporter.
+    private sealed class SyncProgress<T>(Action<T> report) : IProgress<T>
+    {
+        public void Report(T value) => report(value);
+    }
+
+
+    [Fact]
+    public void ResolveUrl_uses_the_configured_port()
+    {
+        var url = RegisterMcpStep.ResolveUrl(new InstallerWorkerConfig { ExternalMcpPort = 49999 });
+
+        Assert.Equal("http://127.0.0.1:49999/mcp", url);
+    }
+
+    [Fact]
+    public void ResolveUrl_defaults_to_47822_without_a_configured_port()
+    {
+        var url = RegisterMcpStep.ResolveUrl(new InstallerWorkerConfig());
+
+        Assert.Equal("http://127.0.0.1:47822/mcp", url);
+    }
+
+    [Fact]
+    public void ResolveUrl_is_null_when_the_external_listener_is_disabled()
+    {
+        var url = RegisterMcpStep.ResolveUrl(new InstallerWorkerConfig { ExternalMcpPort = 0 });
+
+        Assert.Null(url);
+    }
+
+    [Fact]
+    public async Task Not_selected_skips_without_loading_the_worker_config()
+    {
+        var loaded = false;
+        var step = new RegisterMcpStep(() => { loaded = true; return new InstallerWorkerConfig(); });
+        var ctx = new InstallContext { RegisterMcpWithClaude = false };
+
+        var result = await step.ExecuteAsync(ctx, new Progress<string>(_ => { }), CancellationToken.None);
+
+        Assert.True(result.Success);
+        Assert.False(loaded);
+    }
+
+    [Fact]
+    public async Task Disabled_external_port_skips_without_running_the_claude_cli()
+    {
+        var step = new RegisterMcpStep(() => new InstallerWorkerConfig { ExternalMcpPort = 0 });
+        var ctx = new InstallContext { RegisterMcpWithClaude = true };
+        var messages = new List<string>();
+
+        var result = await step.ExecuteAsync(ctx, new SyncProgress<string>(messages.Add), CancellationToken.None);
+
+        Assert.True(result.Success);
+        Assert.Contains(messages, m => m.Contains("external_mcp_port is 0", StringComparison.Ordinal));
+    }
+}