fix(import): tolerate numeric my_rotation_id; skip empty deck slots

A real /load/index dump emits my_rotation_id as a bare number (0) for
unset MyRotation slots, which 400'd against the string? DTO field
(AllowReadingFromString only covers string->number). FlexibleStringConverter
accepts either form. Also skip empty deck slots (no cards) on import — a
dump carries every slot, mostly empty placeholders the client manages
itself.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

SVSim.EmulatedEntrypoint/Controllers/AdminController.cs

@@ -206,6 +206,12 @@ public class AdminController : SVSimController
 
             foreach (var d in request.Decks)
             {
+                // A /load/index dump carries every deck slot, most of them empty placeholders
+                // (no cards). Skip them: the client manages empty slots itself (it's why the old
+                // default-deck cloning was removed), and importing empty MyRotation slots would
+                // otherwise persist decks with a bogus rotation id.
+                if ((d.CardIdArray?.Count ?? 0) == 0) continue;
+
                 Format format;
                 try { format = FormatExtensions.FromApi(d.DeckFormat); }
                 catch (ArgumentOutOfRangeException) { continue; } // skip unsupported wire format

SVSim.EmulatedEntrypoint/Models/Dtos/Common/FlexibleStringConverter.cs

@@ -0,0 +1,29 @@
+using System.Globalization;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.Common;
+
+/// <summary>
+/// Reads a JSON string OR number as a nullable string, tolerating prod's polymorphic id fields.
+/// <c>rotation_id</c> on a /load/index <c>UserDeck</c> is a numeric string ("10008") for real
+/// MyRotation decks but a bare number (<c>0</c>) for unset slots — and the global
+/// <c>AllowReadingFromString</c> only covers the string→number direction, not number→string, so a
+/// plain <c>string?</c> property 400s on the numeric form. Null stays null; numbers serialize via
+/// invariant culture so a captured <c>0</c> round-trips to <c>"0"</c>.
+/// </summary>
+public sealed class FlexibleStringConverter : JsonConverter<string?>
+{
+    public override string? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options) =>
+        reader.TokenType switch
+        {
+            JsonTokenType.Null => null,
+            JsonTokenType.String => reader.GetString(),
+            JsonTokenType.Number when reader.TryGetInt64(out var n) => n.ToString(CultureInfo.InvariantCulture),
+            JsonTokenType.Number => reader.GetDouble().ToString(CultureInfo.InvariantCulture),
+            _ => throw new JsonException($"Unexpected token {reader.TokenType} for a string-or-number field.")
+        };
+
+    public override void Write(Utf8JsonWriter writer, string? value, JsonSerializerOptions options) =>
+        writer.WriteStringValue(value);
+}

SVSim.EmulatedEntrypoint/Models/Dtos/Requests/Admin/ImportViewerRequest.cs

@@ -1,4 +1,5 @@
 using System.Text.Json.Serialization;
+using SVSim.EmulatedEntrypoint.Models.Dtos.Common;
 
 namespace SVSim.EmulatedEntrypoint.Models.Dtos.Requests.Admin;
 
@@ -44,7 +45,11 @@ public class ImportDeck
     [JsonPropertyName("sleeve_id")]             public long? SleeveId { get; set; }
     [JsonPropertyName("leader_skin_id")]        public int? LeaderSkinId { get; set; }
     [JsonPropertyName("is_random_leader_skin")] public int? IsRandomLeaderSkin { get; set; }
-    [JsonPropertyName("my_rotation_id")]        public string? MyRotationId { get; set; }
+    // Prod emits rotation_id as a numeric string ("10008") for real MyRotation decks but a bare
+    // number (0) for unset slots; FlexibleStringConverter accepts either (a plain string? 400s on
+    // the numeric form because AllowReadingFromString only covers string→number).
+    [JsonPropertyName("my_rotation_id")] [JsonConverter(typeof(FlexibleStringConverter))]
+    public string? MyRotationId { get; set; }
 }
 
 public class ImportCurrency

SVSim.UnitTests/Controllers/AdminControllerTests.cs

@@ -400,4 +400,54 @@ public class AdminControllerTests
         Assert.That(stored.Decks.Any(d => d.Name == "Wire Deck" && d.Format == Format.Rotation), Is.True,
             "decks snake_case keys must bind (deck_format/deck_no/class_id/card_id_array/...).");
     }
+
+    [Test]
+    public async Task ImportViewer_tolerates_numeric_my_rotation_id_and_skips_empty_decks()
+    {
+        using var factory = new SVSimTestFactory();
+        const ulong steamId = 76_561_198_111_222_341UL;
+        long viewerId = await factory.SeedViewerAsync(steamId: steamId);
+
+        int classId, leaderSkinId; long sleeveId;
+        using (var scope = factory.Services.CreateScope())
+        {
+            var db = scope.ServiceProvider.GetRequiredService<SVSimDbContext>();
+            classId = (await db.Classes.FirstAsync()).Id;
+            sleeveId = (await db.Sleeves.FirstAsync()).Id;
+            leaderSkinId = (await db.LeaderSkins.FirstAsync()).Id;
+        }
+
+        // Mirrors a real prod dump: empty MyRotation slots carry "my_rotation_id": 0 (a NUMBER,
+        // not a string), and dozens of empty slots accompany the few real decks.
+        string json = $$"""
+        {
+          "steam_id": {{steamId}},
+          "decks": [
+            { "deck_format": 2, "deck_no": 1, "deck_name": "Real", "class_id": {{classId}},
+              "sleeve_id": {{sleeveId}}, "leader_skin_id": {{leaderSkinId}},
+              "is_random_leader_skin": 0, "card_id_array": [10001001, 10001002] },
+            { "deck_format": 5, "deck_no": 1, "deck_name": "", "class_id": 0,
+              "sleeve_id": 3000011, "leader_skin_id": 0, "is_random_leader_skin": 0,
+              "my_rotation_id": 0, "card_id_array": [] },
+            { "deck_format": 1, "deck_no": 3, "deck_name": "", "class_id": 1,
+              "sleeve_id": 3000011, "leader_skin_id": 0, "is_random_leader_skin": 0,
+              "card_id_array": [] }
+          ]
+        }
+        """;
+
+        using var client = factory.CreateClient();
+        using var content = new StringContent(json, System.Text.Encoding.UTF8, "application/json");
+        var response = await client.PostAsync("/admin/import_viewer", content);
+
+        Assert.That(response.StatusCode, Is.EqualTo(HttpStatusCode.OK),
+            await response.Content.ReadAsStringAsync());
+
+        using var scope2 = factory.Services.CreateScope();
+        var db2 = scope2.ServiceProvider.GetRequiredService<SVSimDbContext>();
+        var stored = await db2.Viewers.Include(v => v.Decks).FirstAsync(v => v.Id == viewerId);
+        Assert.That(stored.Decks.Count, Is.EqualTo(1),
+            "Empty deck slots must be skipped; only the real (non-empty) deck imports.");
+        Assert.That(stored.Decks.Single().Name, Is.EqualTo("Real"));
+    }
 }