diff --git a/src/ClaudeDo.Installer/Steps/StartServiceStep.cs b/src/ClaudeDo.Installer/Steps/StartServiceStep.cs
new file mode 100644
index 0000000..270c179
--- /dev/null
+++ b/src/ClaudeDo.Installer/Steps/StartServiceStep.cs
@@ -0,0 +1,27 @@
+using ClaudeDo.Installer.Core;
+
+namespace ClaudeDo.Installer.Steps;
+
+public sealed class StartServiceStep : IInstallStep
+{
+    private const string ServiceName = StopServiceStep.ServiceName;
+
+    public string Name => "Start Worker Service";
+
+    public async Task<StepResult> ExecuteAsync(InstallContext ctx, IProgress<string> progress, CancellationToken ct)
+    {
+        progress.Report($"Starting {ServiceName}...");
+
+        var (exit, output) = await ProcessRunner.RunAsync("sc.exe", $"start {ServiceName}", null, progress, ct);
+        if (exit == 0) return StepResult.Ok();
+
+        // Exit 1056 = already running — that's fine too.
+        if (output.Contains("1056", StringComparison.OrdinalIgnoreCase))
+        {
+            progress.Report("Service was already running.");
+            return StepResult.Ok();
+        }
+
+        return StepResult.Fail($"sc.exe start failed with exit code {exit}");
+    }
+}
diff --git a/src/ClaudeDo.Installer/Steps/StopServiceStep.cs b/src/ClaudeDo.Installer/Steps/StopServiceStep.cs
new file mode 100644
index 0000000..be3c271
--- /dev/null
+++ b/src/ClaudeDo.Installer/Steps/StopServiceStep.cs
@@ -0,0 +1,48 @@
+using ClaudeDo.Installer.Core;
+
+namespace ClaudeDo.Installer.Steps;
+
+public sealed class StopServiceStep : IInstallStep
+{
+    public const string ServiceName = "ClaudeDoWorker";
+
+    public string Name => "Stop Worker Service";
+
+    public async Task<StepResult> ExecuteAsync(InstallContext ctx, IProgress<string> progress, CancellationToken ct)
+    {
+        progress.Report($"Stopping {ServiceName} (if running)...");
+
+        // sc.exe query -> returns non-zero if the service does not exist; that's fine.
+        var (queryExit, queryOutput) = await ProcessRunner.RunAsync("sc.exe", $"query {ServiceName}", null, progress, ct);
+        if (queryExit != 0)
+        {
+            progress.Report("Service is not registered — nothing to stop.");
+            return StepResult.Ok();
+        }
+
+        if (queryOutput.Contains("STOPPED", StringComparison.OrdinalIgnoreCase))
+        {
+            progress.Report("Service is already stopped.");
+            return StepResult.Ok();
+        }
+
+        var (stopExit, _) = await ProcessRunner.RunAsync("sc.exe", $"stop {ServiceName}", null, progress, ct);
+        if (stopExit != 0)
+            return StepResult.Fail($"sc.exe stop failed with exit code {stopExit}");
+
+        // Poll until stopped or timeout (up to 30s).
+        for (var i = 0; i < 30; i++)
+        {
+            ct.ThrowIfCancellationRequested();
+            await Task.Delay(1000, ct);
+            var (e, o) = await ProcessRunner.RunAsync("sc.exe", $"query {ServiceName}", null, progress, ct);
+            if (e != 0 || o.Contains("STOPPED", StringComparison.OrdinalIgnoreCase))
+            {
+                progress.Report("Service stopped.");
+                return StepResult.Ok();
+            }
+        }
+
+        return StepResult.Fail("Service did not stop within 30 seconds.");
+    }
+}