feat(toolbox): preconfig store (load fail-open, clear-pin, configured marker)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

windows/welcome/src/SilverOS.Welcome.Core/Preconfig/IPreconfigStore.cs

@@ -0,0 +1,9 @@
+namespace SilverOS.Welcome.Core.Preconfig;
+
+public interface IPreconfigStore
+{
+    Preconfig? Load();          // null if missing/corrupt (fail-open)
+    void ClearPin();            // rewrite preconfig without the BitLocker pin
+    bool IsConfigured();        // configured marker present?
+    void MarkConfigured();      // write the configured marker
+}

windows/welcome/src/SilverOS.Welcome.Core/Preconfig/Preconfig.cs

@@ -0,0 +1,22 @@
+using System.Text.Json;
+
+namespace SilverOS.Welcome.Core.Preconfig;
+
+public sealed record BitlockerConfig { public bool Enable { get; init; } public string? Pin { get; init; } }
+public sealed record AppsConfig { public bool UseFlavourDefaults { get; init; } = true; public IReadOnlyList<string>? Selected { get; init; } }
+
+public sealed record Preconfig
+{
+    public int SchemaVersion { get; init; } = 1;
+    public string Flavour { get; init; } = "";
+    public BitlockerConfig Bitlocker { get; init; } = new();
+    public AppsConfig Apps { get; init; } = new();
+
+    public static readonly JsonSerializerOptions JsonOptions = new()
+    {
+        PropertyNameCaseInsensitive = true,
+        ReadCommentHandling = JsonCommentHandling.Skip,
+        AllowTrailingCommas = true,
+        DefaultIgnoreCondition = System.Text.Json.Serialization.JsonIgnoreCondition.WhenWritingNull
+    };
+}

windows/welcome/src/SilverOS.Welcome.Core/Preconfig/PreconfigStore.cs

@@ -0,0 +1,30 @@
+using System.Text.Json;
+
+namespace SilverOS.Welcome.Core.Preconfig;
+
+public sealed class PreconfigStore(string dir) : IPreconfigStore
+{
+    private string File_ => Path.Combine(dir, "preconfig.json");
+    private string Marker => Path.Combine(dir, "configured");
+
+    public Preconfig? Load()
+    {
+        try
+        {
+            if (!File.Exists(File_)) return null;
+            return JsonSerializer.Deserialize<Preconfig>(File.ReadAllText(File_), Preconfig.JsonOptions);
+        }
+        catch (JsonException) { return null; }   // fail-open
+    }
+
+    public void ClearPin()
+    {
+        var p = Load();
+        if (p is null) return;
+        var stripped = p with { Bitlocker = p.Bitlocker with { Pin = null } };
+        File.WriteAllText(File_, JsonSerializer.Serialize(stripped, Preconfig.JsonOptions));
+    }
+
+    public bool IsConfigured() => File.Exists(Marker);
+    public void MarkConfigured() { Directory.CreateDirectory(dir); File.WriteAllText(Marker, "1"); }
+}

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

@@ -0,0 +1,64 @@
+using System.IO;
+using System.Text.Json;
+using SilverOS.Welcome.Core.Preconfig;
+using Xunit;
+
+public class PreconfigTests
+{
+    static string TempDir()
+    {
+        var d = Path.Combine(Path.GetTempPath(), "smpre-" + System.Guid.NewGuid().ToString("N"));
+        Directory.CreateDirectory(d);
+        return d;
+    }
+
+    const string Sample = """
+    { "schemaVersion":1, "flavour":"developer",
+      "bitlocker":{"enable":true,"pin":"246810"},
+      "apps":{"useFlavourDefaults":true} }
+    """;
+
+    [Fact]
+    public void Loads_flavour_and_pin()
+    {
+        var dir = TempDir();
+        File.WriteAllText(Path.Combine(dir, "preconfig.json"), Sample);
+        var p = new PreconfigStore(dir).Load();
+        Assert.NotNull(p);
+        Assert.Equal("developer", p!.Flavour);
+        Assert.True(p.Bitlocker.Enable);
+        Assert.Equal("246810", p.Bitlocker.Pin);
+        Assert.True(p.Apps.UseFlavourDefaults);
+    }
+
+    [Fact]
+    public void Missing_or_bad_file_returns_null_not_throw()
+    {
+        Assert.Null(new PreconfigStore(TempDir()).Load());            // missing
+        var dir = TempDir();
+        File.WriteAllText(Path.Combine(dir, "preconfig.json"), "{ not json");
+        Assert.Null(new PreconfigStore(dir).Load());                 // corrupt
+    }
+
+    [Fact]
+    public void ClearPin_rewrites_without_the_pin()
+    {
+        var dir = TempDir();
+        File.WriteAllText(Path.Combine(dir, "preconfig.json"), Sample);
+        var store = new PreconfigStore(dir);
+        store.ClearPin();
+        var reread = store.Load();
+        Assert.True(string.IsNullOrEmpty(reread!.Bitlocker.Pin));
+        Assert.Equal("developer", reread.Flavour); // rest preserved
+    }
+
+    [Fact]
+    public void Configured_marker_roundtrips()
+    {
+        var dir = TempDir();
+        var store = new PreconfigStore(dir);
+        Assert.False(store.IsConfigured());
+        store.MarkConfigured();
+        Assert.True(store.IsConfigured());
+    }
+}