feat(welcome): process runner abstraction

windows/welcome/src/SilverOS.Welcome.Core/Apply/IProcessRunner.cs

@@ -0,0 +1,6 @@
+namespace SilverOS.Welcome.Core.Apply;
+public readonly record struct ProcessResult(int ExitCode, string StdOut, string StdErr);
+public interface IProcessRunner
+{
+    Task<ProcessResult> RunAsync(string file, string args, CancellationToken ct = default);
+}

windows/welcome/src/SilverOS.Welcome.Core/Apply/ProcessRunner.cs

@@ -0,0 +1,19 @@
+using System.Diagnostics;
+namespace SilverOS.Welcome.Core.Apply;
+
+public sealed class ProcessRunner : IProcessRunner
+{
+    public async Task<ProcessResult> RunAsync(string file, string args, CancellationToken ct = default)
+    {
+        using var p = new Process { StartInfo = new ProcessStartInfo(file, args)
+        {
+            RedirectStandardOutput = true, RedirectStandardError = true,
+            UseShellExecute = false, CreateNoWindow = true
+        }};
+        p.Start();
+        var outT = p.StandardOutput.ReadToEndAsync(ct);
+        var errT = p.StandardError.ReadToEndAsync(ct);
+        await p.WaitForExitAsync(ct);
+        return new ProcessResult(p.ExitCode, await outT, await errT);
+    }
+}

windows/welcome/tests/SilverOS.Welcome.Tests/ProcessRunnerTests.cs

@@ -0,0 +1,14 @@
+using SilverOS.Welcome.Core.Apply;
+using Xunit;
+
+public class ProcessRunnerTests
+{
+    [Fact]
+    public async Task Runs_powershell_and_captures_output_and_exit()
+    {
+        var r = await new ProcessRunner().RunAsync(
+            "powershell.exe", "-NoProfile -Command \"Write-Output hello; exit 3\"");
+        Assert.Equal(3, r.ExitCode);
+        Assert.Contains("hello", r.StdOut);
+    }
+}