feat(pack): /pack/set_rotation_starter_class + selected_class_id read-back

Implements Task 9 from docs/superpowers/plans/2026-06-13-decomp-only-followups.md
— the pre-purchase commit endpoint the client fires from StarterClassSelectDialog
before opening a RotationStarterCardPack. Without this the per-class draw path
from yesterday's work is unreachable: the dialog blocks on the AJAX call and
never advances to /pack/open.

Wire surface:
- POST /pack/set_rotation_starter_class { pack_id, class_id } → EmptyData.
  Validates 1..8, rejects unknown packs (404), non-RS packs (400), and second
  commits (400 — one-shot per pack per spec).
- PackConfigDto carries selected_class_id (nullable, omitted via global
  WhenWritingNull policy when unset). Placement verified against decomp at
  PackInfoTask.cs:86 — it's on the parent PackConfig, NOT the child gacha as
  the original plan text had it.
- /pack/open cross-checks request.class_id against the persisted choice for
  RS packs; rejects 400 on missing-commit or class-mismatch so a tampered
  request can't swap pools after the choice is locked.

Storage:
- ViewerPackStarterClass owned entity; (ViewerId, PackId) unique index via the
  pattern from project_owned_collection_unique_index memory.
- Migration PackStarterClass — composite PK + FK cascade verified against
  fresh Postgres bootstrap.

Tests (9 new in PackControllerSetRotationStarterClassTests):
- Round-trip set → /pack/info shows selected_class_id.
- Field absent before any commit.
- Invalid class (0/9/-1/100) → 400.
- Already-chosen rejection.
- Non-RS pack / unknown pack rejection.
- /pack/open rejects no-prior-commit AND class-mismatch; succeeds when class
  matches the persisted choice.

Full suite: 1552 passed (1543 + 9).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

SVSim.Database/Migrations/20260627235051_PackStarterClass.cs

@@ -0,0 +1,49 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+using Npgsql.EntityFrameworkCore.PostgreSQL.Metadata;
+
+#nullable disable
+
+namespace SVSim.Database.Migrations
+{
+    /// <inheritdoc />
+    public partial class PackStarterClass : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.CreateTable(
+                name: "ViewerPackStarterClass",
+                columns: table => new
+                {
+                    ViewerId = table.Column<long>(type: "bigint", nullable: false),
+                    Id = table.Column<int>(type: "integer", nullable: false)
+                        .Annotation("Npgsql:ValueGenerationStrategy", NpgsqlValueGenerationStrategy.IdentityByDefaultColumn),
+                    PackId = table.Column<int>(type: "integer", nullable: false),
+                    ClassId = table.Column<int>(type: "integer", nullable: false)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_ViewerPackStarterClass", x => new { x.ViewerId, x.Id });
+                    table.ForeignKey(
+                        name: "FK_ViewerPackStarterClass_Viewers_ViewerId",
+                        column: x => x.ViewerId,
+                        principalTable: "Viewers",
+                        principalColumn: "Id",
+                        onDelete: ReferentialAction.Cascade);
+                });
+
+            migrationBuilder.CreateIndex(
+                name: "IX_ViewerPackStarterClass_ViewerId_PackId",
+                table: "ViewerPackStarterClass",
+                columns: new[] { "ViewerId", "PackId" },
+                unique: true);
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropTable(
+                name: "ViewerPackStarterClass");
+        }
+    }
+}

SVSim.Database/Migrations/SVSimDbContextModelSnapshot.cs

@@ -4809,6 +4809,34 @@ namespace SVSim.Database.Migrations
                                 .HasForeignKey("ViewerId");
                         });
 
+                    b.OwnsMany("SVSim.Database.Models.ViewerPackStarterClass", "PackStarterClasses", b1 =>
+                        {
+                            b1.Property<long>("ViewerId")
+                                .HasColumnType("bigint");
+
+                            b1.Property<int>("Id")
+                                .ValueGeneratedOnAdd()
+                                .HasColumnType("integer");
+
+                            NpgsqlPropertyBuilderExtensions.UseIdentityByDefaultColumn(b1.Property<int>("Id"));
+
+                            b1.Property<int>("ClassId")
+                                .HasColumnType("integer");
+
+                            b1.Property<int>("PackId")
+                                .HasColumnType("integer");
+
+                            b1.HasKey("ViewerId", "Id");
+
+                            b1.HasIndex("ViewerId", "PackId")
+                                .IsUnique();
+
+                            b1.ToTable("ViewerPackStarterClass");
+
+                            b1.WithOwner()
+                                .HasForeignKey("ViewerId");
+                        });
+
                     b.Navigation("BuildDeckPurchases");
 
                     b.Navigation("Cards");
@@ -4838,6 +4866,8 @@ namespace SVSim.Database.Migrations
 
                     b.Navigation("PackOpenCounts");
 
+                    b.Navigation("PackStarterClasses");
+
                     b.Navigation("SocialAccountConnections");
                 });
 

SVSim.Database/Models/Viewer.cs

@@ -83,6 +83,8 @@ public class Viewer : BaseEntity<long>
 
     public List<ViewerPackOpenCount> PackOpenCounts { get; set; } = new List<ViewerPackOpenCount>();
 
+    public List<ViewerPackStarterClass> PackStarterClasses { get; set; } = new List<ViewerPackStarterClass>();
+
     public List<ViewerFreePackClaim> FreePackClaims { get; set; } = new List<ViewerFreePackClaim>();
 
     public List<MyPageBgRotationEntry> MyPageBgRotation { get; set; } = new List<MyPageBgRotationEntry>();

SVSim.Database/Models/ViewerPackStarterClass.cs

@@ -0,0 +1,17 @@
+using Microsoft.EntityFrameworkCore;
+
+namespace SVSim.Database.Models;
+
+/// <summary>
+/// Records a viewer's class choice for a <see cref="Enums.PackCategory.RotationStarterCardPack"/>.
+/// One row per (Viewer, Pack) — the choice is one-shot per pack per
+/// /pack/set_rotation_starter_class spec. Surfaces as <c>selected_class_id</c> on the parent
+/// PackConfig in the next /pack/info response so the client's starter-pack dialog can
+/// pre-select on revisit. <see cref="PackId"/> = parent_gacha_id; <see cref="ClassId"/> is 1..8.
+/// </summary>
+[Owned]
+public class ViewerPackStarterClass
+{
+    public int PackId { get; set; }
+    public int ClassId { get; set; }
+}

SVSim.Database/SVSimDbContext.cs

@@ -184,6 +184,13 @@ public class SVSimDbContext : DbContext
             e.HasIndex(x => new { x.PackId, x.Slot, x.Tier });
         });
         modelBuilder.Entity<Viewer>().OwnsMany(v => v.PackOpenCounts);
+        modelBuilder.Entity<Viewer>().OwnsMany(v => v.PackStarterClasses, b =>
+        {
+            // One choice per (viewer, pack) — /pack/set_rotation_starter_class is one-shot
+            // per pack. Mirrors the (ViewerId, PackId) unique-index pattern used by
+            // GachaPointBalances above (project_owned_collection_unique_index memory).
+            b.HasIndex("ViewerId", nameof(ViewerPackStarterClass.PackId)).IsUnique();
+        });
         modelBuilder.Entity<Viewer>().OwnsMany(v => v.FreePackClaims, b =>
         {
             b.WithOwner().HasForeignKey("ViewerId");

SVSim.EmulatedEntrypoint/Controllers/PackController.cs

@@ -7,6 +7,7 @@ using SVSim.Database.Models;
 using SVSim.Database.Repositories.Pack;
 using SVSim.Database.Repositories.PackDrawTables;
 using SVSim.EmulatedEntrypoint.Models.Dtos;
+using SVSim.EmulatedEntrypoint.Models.Dtos.Common;
 using SVSim.EmulatedEntrypoint.Models.Dtos.Requests;
 using SVSim.EmulatedEntrypoint.Models.Dtos.Requests.Pack;
 using SVSim.EmulatedEntrypoint.Models.Dtos.Responses.Pack;
@@ -101,10 +102,20 @@ public class PackController : SVSimController
             .Select(c => new { c.FreeGachaCampaignId, c.LastClaimedAt, c.ClaimCount })
             .ToDictionaryAsync(x => x.FreeGachaCampaignId, x => (x.LastClaimedAt, x.ClaimCount));
 
+        // Per-viewer RotationStarter class choices keyed by pack id — populates
+        // selected_class_id on the parent PackConfigDto so the client's
+        // StarterClassSelectDialog can pre-select on revisit (PackInfoTask.cs:86 reads via
+        // TryGetValue, so absent-key for non-RS packs is intentional/safe).
+        var starterClassesByPackId = await _db.Viewers
+            .Where(v => v.Id == viewerId)
+            .SelectMany(v => v.PackStarterClasses)
+            .Select(s => new { s.PackId, s.ClassId })
+            .ToDictionaryAsync(x => x.PackId, x => x.ClassId);
+
         return new PackInfoResponse
         {
             PackConfigList = packs
-                .Select(p => ToDto(p, openCounts, ownedItemsByItemId, gachaPointBalancesByPackId, freeClaimsByCampaignId))
+                .Select(p => ToDto(p, openCounts, ownedItemsByItemId, gachaPointBalancesByPackId, freeClaimsByCampaignId, starterClassesByPackId))
                 .ToList(),
         };
     }
@@ -114,7 +125,8 @@ public class PackController : SVSimController
         IReadOnlyDictionary<int, ViewerPackOpenCount> openCounts,
         IReadOnlyDictionary<long, int> ownedItemsByItemId,
         IReadOnlyDictionary<int, int> gachaPointBalancesByPackId,
-        IReadOnlyDictionary<int, (DateTime LastClaimedAt, int ClaimCount)> freeClaimsByCampaignId)
+        IReadOnlyDictionary<int, (DateTime LastClaimedAt, int ClaimCount)> freeClaimsByCampaignId,
+        IReadOnlyDictionary<int, int> starterClassesByPackId)
     {
         int openCount = openCounts.TryGetValue(p.Id, out var oc) ? oc.OpenCount : 0;
 
@@ -204,6 +216,7 @@ public class PackController : SVSimController
             OpenCountLimit = p.OpenCountLimit,
             IsHide = p.IsHide ? 1 : 0,
             PackCategory = (int)p.PackCategory,
+            SelectedClassId = starterClassesByPackId.TryGetValue(p.Id, out var chosenClass) ? chosenClass : null,
             GachaPoint = gachaPointDto,
             IsPreRelease = p.IsPreRelease,
             ExistsPurchaseReward = false,
@@ -259,6 +272,43 @@ public class PackController : SVSimController
         };
     }
 
+    /// <summary>
+    /// /pack/set_rotation_starter_class — lock in the class for a RotationStarterCardPack.
+    /// One-shot per (viewer, pack); rejects the second attempt with 400. The client opens
+    /// the pack via /pack/open afterwards (see Wizard/StarterClassSelectDialog.cs which
+    /// chains this call into StarterPurchaseConfirmationDialog on 200).
+    /// </summary>
+    [HttpPost("set_rotation_starter_class")]
+    public async Task<ActionResult<EmptyResponse>> SetRotationStarterClass(
+        PackSetRotationStarterClassRequest request, CancellationToken ct)
+    {
+        if (!TryGetViewerId(out long viewerId)) return Unauthorized();
+
+        if (request.ClassId is < 1 or > 8)
+            return BadRequest(new { error = "invalid_class" });
+
+        var pack = await _packs.GetPack(request.PackId);
+        if (pack is null) return NotFound(new { error = "unknown_pack" });
+        if (pack.PackCategory != PackCategory.RotationStarterCardPack)
+            return BadRequest(new { error = "not_a_rotation_starter_pack" });
+
+        var viewer = await _db.Viewers
+            .Include(v => v.PackStarterClasses)
+            .FirstOrDefaultAsync(v => v.Id == viewerId, ct);
+        if (viewer is null) return Unauthorized();
+
+        if (viewer.PackStarterClasses.Any(s => s.PackId == request.PackId))
+            return BadRequest(new { error = "class_already_chosen" });
+
+        viewer.PackStarterClasses.Add(new ViewerPackStarterClass
+        {
+            PackId = request.PackId,
+            ClassId = request.ClassId,
+        });
+        await _db.SaveChangesAsync(ct);
+        return new EmptyResponse();
+    }
+
     [HttpPost("get_leader_skin_owned_status")]
     public ActionResult<Dictionary<string, Dictionary<string, object>>> GetLeaderSkinOwnedStatus(
         [FromBody] PackGetLeaderSkinOwnedStatusRequest _)
@@ -299,12 +349,25 @@ public class PackController : SVSimController
         // Rotation-starter packs require a class_id (1..8) to select the per-class card pool.
         // Reject if missing/out-of-range; reject class_id on non-RS packs so it can't sneak
         // through and pick up nothing (a class-filtered draw against a non-RS pack would
-        // return an empty pool and 500).
+        // return an empty pool and 500). For RS packs the client is expected to have already
+        // committed the choice via /pack/set_rotation_starter_class — cross-check that the
+        // request class matches the persisted one so a tampered request can't swap pools
+        // mid-flight.
         bool isRotationStarter = pack.PackCategory == PackCategory.RotationStarterCardPack;
         if (isRotationStarter)
         {
             if (request.ClassId is not int cid || cid < 1 || cid > 8)
                 return BadRequest(new { error = "class_id_required_for_rotation_starter" });
+            var persisted = await _db.Viewers
+                .Where(v => v.Id == viewerId)
+                .SelectMany(v => v.PackStarterClasses)
+                .Where(s => s.PackId == request.ParentGachaId)
+                .Select(s => (int?)s.ClassId)
+                .FirstOrDefaultAsync();
+            if (persisted is null)
+                return BadRequest(new { error = "rotation_starter_class_not_chosen" });
+            if (persisted != cid)
+                return BadRequest(new { error = "rotation_starter_class_mismatch" });
         }
         else if (request.ClassId.HasValue)
         {

SVSim.EmulatedEntrypoint/Models/Dtos/PackConfigDto.cs

@@ -118,4 +118,14 @@ public class PackConfigDto
     [JsonPropertyName("poster_type")]
     [Key("poster_type")]
     public int PosterType { get; set; }
+
+    /// <summary>
+    /// The viewer's already-chosen class for a RotationStarterCardPack (1..8). Null when the
+    /// viewer has not yet locked a choice via /pack/set_rotation_starter_class. Client at
+    /// PackInfoTask.cs:86 reads via <c>TryGetValue</c>, so a missing key is safe (don't emit
+    /// when null — global WhenWritingNull is sufficient here).
+    /// </summary>
+    [JsonPropertyName("selected_class_id")]
+    [Key("selected_class_id")]
+    public int? SelectedClassId { get; set; }
 }

SVSim.EmulatedEntrypoint/Models/Dtos/Requests/Pack/PackSetRotationStarterClassRequest.cs

@@ -0,0 +1,23 @@
+using System.Text.Json.Serialization;
+using MessagePack;
+using SVSim.EmulatedEntrypoint.Models.Dtos.Requests;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.Requests.Pack;
+
+/// <summary>
+/// Inbound /pack/set_rotation_starter_class body. Locks in the class choice for a
+/// RotationStarterCardPack before the user can open it. One-shot per (viewer, pack)
+/// per the spec; subsequent attempts return 400.
+/// See <c>Wizard/PackSetRotationStarterClassTask.cs</c>.
+/// </summary>
+[MessagePackObject]
+public class PackSetRotationStarterClassRequest : BaseRequest
+{
+    [JsonPropertyName("pack_id")]
+    [Key("pack_id")]
+    public int PackId { get; set; }
+
+    [JsonPropertyName("class_id")]
+    [Key("class_id")]
+    public int ClassId { get; set; }
+}

SVSim.UnitTests/Controllers/PackControllerSetRotationStarterClassTests.cs

@@ -0,0 +1,232 @@
+using System.Net;
+using System.Text;
+using System.Text.Json;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.DependencyInjection;
+using SVSim.Database;
+using SVSim.Database.Enums;
+using SVSim.Database.Models;
+using SVSim.UnitTests.Infrastructure;
+
+namespace SVSim.UnitTests.Controllers;
+
+public class PackControllerSetRotationStarterClassTests
+{
+    private static StringContent JsonBody(string json) => new(json, Encoding.UTF8, "application/json");
+
+    /// <summary>
+    /// Seeds an active RotationStarterCardPack (id 93025) with a minimal class-1-only draw table
+    /// sufficient to satisfy /pack/open after a class is locked in. The class-axis sampling in
+    /// PackOpenService is covered by PackOpenServiceTests; this helper only needs a working table.
+    /// Returns the pack id.
+    /// </summary>
+    private static async Task<int> SeedRotationStarterPack(SVSimTestFactory f, long viewerId, int packId = 93025, ulong rupees = 5000)
+    {
+        using var scope = f.Services.CreateScope();
+        var db = scope.ServiceProvider.GetRequiredService<SVSimDbContext>();
+        var set = await db.CardSets.Include(s => s.Cards).FirstAsync(s => s.Cards.Count > 0);
+        int baseId = set.Id;
+        long cardId = set.Cards.First().Id;
+
+        db.Packs.Add(new PackConfigEntry
+        {
+            Id = packId,
+            BasePackId = baseId,
+            PackCategory = PackCategory.RotationStarterCardPack,
+            CommenceDate = DateTime.UtcNow.AddDays(-1),
+            CompleteDate = DateTime.UtcNow.AddDays(30),
+            GachaType = 1,
+            GachaDetail = "rs-test",
+            SleeveId = 3000011,
+            ChildGachas = {
+                new PackChildGachaEntry { GachaId = packId * 10 + 1, TypeDetail = CardPackType.RupyMulti, Cost = 100, CardCount = 8 },
+            },
+        });
+
+        db.PackDrawConfigs.Add(new PackDrawConfigEntry { Id = packId, AnimationRatePct = 0 });
+        // Both slots: bronze 100% — single tier keeps the test deterministic.
+        db.PackDrawSlotRates.Add(new PackDrawSlotRateEntry { PackId = packId, Slot = DrawSlot.General, Tier = DrawTier.Bronze, RatePct = 100.0 });
+        db.PackDrawSlotRates.Add(new PackDrawSlotRateEntry { PackId = packId, Slot = DrawSlot.Eighth,  Tier = DrawTier.Bronze, RatePct = 100.0 });
+        // Class 3 pool only — verifies the class filter actually narrows. Open requests for
+        // any other class would fall through to FallbackAcrossTiers and 500 if the test ever
+        // expected them to succeed.
+        db.PackDrawCardWeights.Add(new PackDrawCardWeightEntry { PackId = packId, Slot = DrawSlot.General, Tier = DrawTier.Bronze, ClassId = 3, CardId = cardId, RatePct = 100 });
+        db.PackDrawCardWeights.Add(new PackDrawCardWeightEntry { PackId = packId, Slot = DrawSlot.Eighth,  Tier = DrawTier.Bronze, ClassId = 3, CardId = cardId, RatePct = 100 });
+
+        var v = await db.Viewers.FirstAsync(x => x.Id == viewerId);
+        v.Currency.Rupees = rupees;
+        await db.SaveChangesAsync();
+        return packId;
+    }
+
+    [Test]
+    public async Task SetRotationStarterClass_persists_and_appears_in_pack_info()
+    {
+        using var factory = new SVSimTestFactory();
+        long viewerId = await factory.SeedViewerAsync();
+        int packId = await SeedRotationStarterPack(factory, viewerId);
+
+        using var client = factory.CreateAuthenticatedClient(viewerId);
+        var setJson = $$"""{"viewer_id":"0","steam_id":0,"steam_session_ticket":"","pack_id":{{packId}},"class_id":3}""";
+        var setResp = await client.PostAsync("/pack/set_rotation_starter_class", JsonBody(setJson));
+        Assert.That(setResp.StatusCode, Is.EqualTo(HttpStatusCode.OK));
+
+        var infoResp = await client.PostAsync("/pack/info",
+            JsonBody("""{"viewer_id":"0","steam_id":0,"steam_session_ticket":""}"""));
+        Assert.That(infoResp.StatusCode, Is.EqualTo(HttpStatusCode.OK));
+
+        var body = await infoResp.Content.ReadAsStringAsync();
+        using var doc = JsonDocument.Parse(body);
+        var packs = doc.RootElement.GetProperty("pack_config_list");
+        JsonElement? pack = null;
+        foreach (var p in packs.EnumerateArray())
+        {
+            if (p.GetProperty("parent_gacha_id").GetInt32() == packId) { pack = p; break; }
+        }
+        Assert.That(pack, Is.Not.Null, $"pack {packId} should be present in /pack/info");
+        Assert.That(pack!.Value.TryGetProperty("selected_class_id", out var sel), Is.True,
+            "selected_class_id must be present on the parent PackConfig after the choice");
+        Assert.That(sel.GetInt32(), Is.EqualTo(3));
+    }
+
+    [Test]
+    public async Task SetRotationStarterClass_omits_selected_class_id_before_choice()
+    {
+        using var factory = new SVSimTestFactory();
+        long viewerId = await factory.SeedViewerAsync();
+        int packId = await SeedRotationStarterPack(factory, viewerId);
+
+        using var client = factory.CreateAuthenticatedClient(viewerId);
+        var infoResp = await client.PostAsync("/pack/info",
+            JsonBody("""{"viewer_id":"0","steam_id":0,"steam_session_ticket":""}"""));
+        var body = await infoResp.Content.ReadAsStringAsync();
+        using var doc = JsonDocument.Parse(body);
+        var pack = doc.RootElement.GetProperty("pack_config_list")
+            .EnumerateArray().First(p => p.GetProperty("parent_gacha_id").GetInt32() == packId);
+        // Global WhenWritingNull policy applies — key absent when no choice exists.
+        Assert.That(pack.TryGetProperty("selected_class_id", out _), Is.False,
+            "selected_class_id key must be absent before the viewer has chosen");
+    }
+
+    [Test]
+    public async Task SetRotationStarterClass_rejects_invalid_class()
+    {
+        using var factory = new SVSimTestFactory();
+        long viewerId = await factory.SeedViewerAsync();
+        int packId = await SeedRotationStarterPack(factory, viewerId);
+        using var client = factory.CreateAuthenticatedClient(viewerId);
+
+        foreach (int bad in new[] { 0, 9, -1, 100 })
+        {
+            var json = $$"""{"viewer_id":"0","steam_id":0,"steam_session_ticket":"","pack_id":{{packId}},"class_id":{{bad}}}""";
+            var resp = await client.PostAsync("/pack/set_rotation_starter_class", JsonBody(json));
+            Assert.That(resp.StatusCode, Is.EqualTo(HttpStatusCode.BadRequest), $"class_id={bad} should be rejected");
+        }
+    }
+
+    [Test]
+    public async Task SetRotationStarterClass_rejects_already_chosen()
+    {
+        using var factory = new SVSimTestFactory();
+        long viewerId = await factory.SeedViewerAsync();
+        int packId = await SeedRotationStarterPack(factory, viewerId);
+        using var client = factory.CreateAuthenticatedClient(viewerId);
+
+        var json = $$"""{"viewer_id":"0","steam_id":0,"steam_session_ticket":"","pack_id":{{packId}},"class_id":3}""";
+        var first = await client.PostAsync("/pack/set_rotation_starter_class", JsonBody(json));
+        Assert.That(first.StatusCode, Is.EqualTo(HttpStatusCode.OK));
+
+        var json2 = $$"""{"viewer_id":"0","steam_id":0,"steam_session_ticket":"","pack_id":{{packId}},"class_id":5}""";
+        var second = await client.PostAsync("/pack/set_rotation_starter_class", JsonBody(json2));
+        Assert.That(second.StatusCode, Is.EqualTo(HttpStatusCode.BadRequest),
+            "second commit should be rejected — choice is one-shot per pack");
+    }
+
+    [Test]
+    public async Task SetRotationStarterClass_rejects_non_rotation_starter_pack()
+    {
+        using var factory = new SVSimTestFactory();
+        long viewerId = await factory.SeedViewerAsync();
+        // Seed a standard expansion pack (Category.None) — class lock doesn't apply.
+        using (var scope = factory.Services.CreateScope())
+        {
+            var db = scope.ServiceProvider.GetRequiredService<SVSimDbContext>();
+            int baseId = await db.CardSets.Where(s => s.Cards.Count > 0).Select(s => s.Id).FirstAsync();
+            db.Packs.Add(new PackConfigEntry
+            {
+                Id = 10001, BasePackId = baseId, PackCategory = PackCategory.None,
+                CommenceDate = DateTime.UtcNow.AddDays(-1), CompleteDate = DateTime.UtcNow.AddDays(30),
+                GachaType = 1, GachaDetail = "ord", SleeveId = 3000011,
+            });
+            await db.SaveChangesAsync();
+        }
+
+        using var client = factory.CreateAuthenticatedClient(viewerId);
+        var json = """{"viewer_id":"0","steam_id":0,"steam_session_ticket":"","pack_id":10001,"class_id":3}""";
+        var resp = await client.PostAsync("/pack/set_rotation_starter_class", JsonBody(json));
+        Assert.That(resp.StatusCode, Is.EqualTo(HttpStatusCode.BadRequest));
+    }
+
+    [Test]
+    public async Task SetRotationStarterClass_rejects_unknown_pack()
+    {
+        using var factory = new SVSimTestFactory();
+        long viewerId = await factory.SeedViewerAsync();
+        using var client = factory.CreateAuthenticatedClient(viewerId);
+        var json = """{"viewer_id":"0","steam_id":0,"steam_session_ticket":"","pack_id":99999999,"class_id":3}""";
+        var resp = await client.PostAsync("/pack/set_rotation_starter_class", JsonBody(json));
+        Assert.That(resp.StatusCode, Is.EqualTo(HttpStatusCode.NotFound));
+    }
+
+    [Test]
+    public async Task Open_rs_pack_without_prior_class_commit_is_rejected()
+    {
+        using var factory = new SVSimTestFactory();
+        long viewerId = await factory.SeedViewerAsync();
+        int packId = await SeedRotationStarterPack(factory, viewerId);
+        using var client = factory.CreateAuthenticatedClient(viewerId);
+
+        // Skip /set_rotation_starter_class — go straight to /pack/open with class_id=3.
+        var json = $$"""{"viewer_id":"0","steam_id":0,"steam_session_ticket":"","parent_gacha_id":{{packId}},"gacha_id":{{packId * 10 + 1}},"gacha_type":1,"pack_number":1,"exclude_card_ids":[],"class_id":3}""";
+        var resp = await client.PostAsync("/pack/open", JsonBody(json));
+        Assert.That(resp.StatusCode, Is.EqualTo(HttpStatusCode.BadRequest),
+            "/pack/open on an RS pack must require a prior /set_rotation_starter_class commit");
+    }
+
+    [Test]
+    public async Task Open_rs_pack_rejects_class_id_mismatch()
+    {
+        using var factory = new SVSimTestFactory();
+        long viewerId = await factory.SeedViewerAsync();
+        int packId = await SeedRotationStarterPack(factory, viewerId);
+        using var client = factory.CreateAuthenticatedClient(viewerId);
+
+        // Commit class 3, then attempt to open as class 5.
+        var setJson = $$"""{"viewer_id":"0","steam_id":0,"steam_session_ticket":"","pack_id":{{packId}},"class_id":3}""";
+        var setResp = await client.PostAsync("/pack/set_rotation_starter_class", JsonBody(setJson));
+        Assert.That(setResp.StatusCode, Is.EqualTo(HttpStatusCode.OK));
+
+        var openJson = $$"""{"viewer_id":"0","steam_id":0,"steam_session_ticket":"","parent_gacha_id":{{packId}},"gacha_id":{{packId * 10 + 1}},"gacha_type":1,"pack_number":1,"exclude_card_ids":[],"class_id":5}""";
+        var openResp = await client.PostAsync("/pack/open", JsonBody(openJson));
+        Assert.That(openResp.StatusCode, Is.EqualTo(HttpStatusCode.BadRequest),
+            "/pack/open class_id must match the persisted choice");
+    }
+
+    [Test]
+    public async Task Open_rs_pack_with_matching_class_id_succeeds()
+    {
+        using var factory = new SVSimTestFactory();
+        long viewerId = await factory.SeedViewerAsync();
+        int packId = await SeedRotationStarterPack(factory, viewerId);
+        using var client = factory.CreateAuthenticatedClient(viewerId);
+
+        var setJson = $$"""{"viewer_id":"0","steam_id":0,"steam_session_ticket":"","pack_id":{{packId}},"class_id":3}""";
+        var setResp = await client.PostAsync("/pack/set_rotation_starter_class", JsonBody(setJson));
+        Assert.That(setResp.StatusCode, Is.EqualTo(HttpStatusCode.OK));
+
+        var openJson = $$"""{"viewer_id":"0","steam_id":0,"steam_session_ticket":"","parent_gacha_id":{{packId}},"gacha_id":{{packId * 10 + 1}},"gacha_type":1,"pack_number":1,"exclude_card_ids":[],"class_id":3}""";
+        var openResp = await client.PostAsync("/pack/open", JsonBody(openJson));
+        Assert.That(openResp.StatusCode, Is.EqualTo(HttpStatusCode.OK),
+            $"/pack/open with matching class should succeed; body={await openResp.Content.ReadAsStringAsync()}");
+    }
+}