repo(card): SetProtected with zero-count-row preservation

Implements ICardInventoryRepository.SetProtected — loads only the
owned-cards collection (no decks/currency), guards against the EF
owned-nav Card.Id==0 default-init quirk, and accepts Count=0 rows
(destruct→re-protect round-trip). Covered by 4 new NUnit tests
(flip, unset, zero-count-row, unknown-card error). Full suite: 533/533.

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

SVSim.Database/Repositories/Card/CardInventoryRepository.cs

@@ -154,4 +154,21 @@ public class CardInventoryRepository : ICardInventoryRepository
 
         return CreateOutcome.Ok(new CreateResult(viewer.Currency.RedEther, allGrants));
     }
+
+    public async Task<ProtectOutcome> SetProtected(long viewerId, long cardId, bool isProtected)
+    {
+        // Lighter load than create/destruct: only need viewer's owned-cards collection. No decks,
+        // no currency, no CollectionInfo.
+        var viewer = await _db.Viewers
+            .Include(v => v.Cards).ThenInclude(c => c.Card)
+            .FirstAsync(v => v.Id == viewerId);
+
+        var owned = viewer.Cards.FirstOrDefault(c => c.Card.Id == cardId);
+        if (owned is null || owned.Card.Id == 0)
+            return ProtectOutcome.Fail(ProtectError.UnknownCard);
+
+        owned.IsProtected = isProtected;
+        await _db.SaveChangesAsync();
+        return ProtectOutcome.Ok();
+    }
 }

SVSim.UnitTests/Repositories/CardInventoryRepositoryTests.cs

@@ -514,4 +514,79 @@ public class CardInventoryRepositoryTests
             .FirstAsync(v => v.Id == viewerId);
         Assert.That(viewer.LeaderSkins.Any(s => s.Id == (int)skinId), Is.True, "cascade actually granted the skin");
     }
+
+    [Test]
+    public async Task SetProtected_flips_flag_on_owned_card()
+    {
+        using var factory = new SVSimTestFactory();
+        long viewerId = await factory.SeedViewerAsync();
+        await factory.SeedOwnedCardAsync(viewerId, cardId: 10001001L, count: 2, isProtected: false);
+
+        using var scope = factory.Services.CreateScope();
+        var repo = scope.ServiceProvider.GetRequiredService<ICardInventoryRepository>();
+
+        var outcome = await repo.SetProtected(viewerId, 10001001L, isProtected: true);
+        Assert.That(outcome.IsSuccess, Is.True);
+
+        var db = scope.ServiceProvider.GetRequiredService<SVSimDbContext>();
+        var viewer = await db.Viewers.Include(v => v.Cards).ThenInclude(c => c.Card).FirstAsync(v => v.Id == viewerId);
+        Assert.That(viewer.Cards.First(c => c.Card.Id == 10001001L).IsProtected, Is.True);
+    }
+
+    [Test]
+    public async Task SetProtected_unsets_flag_when_isProtected_false()
+    {
+        using var factory = new SVSimTestFactory();
+        long viewerId = await factory.SeedViewerAsync();
+        await factory.SeedOwnedCardAsync(viewerId, cardId: 10001001L, count: 2, isProtected: true);
+
+        using var scope = factory.Services.CreateScope();
+        var repo = scope.ServiceProvider.GetRequiredService<ICardInventoryRepository>();
+
+        var outcome = await repo.SetProtected(viewerId, 10001001L, isProtected: false);
+        Assert.That(outcome.IsSuccess, Is.True);
+
+        var db = scope.ServiceProvider.GetRequiredService<SVSimDbContext>();
+        var viewer = await db.Viewers.Include(v => v.Cards).ThenInclude(c => c.Card).FirstAsync(v => v.Id == viewerId);
+        Assert.That(viewer.Cards.First(c => c.Card.Id == 10001001L).IsProtected, Is.False);
+    }
+
+    [Test]
+    public async Task SetProtected_allows_zero_count_row()
+    {
+        using var factory = new SVSimTestFactory();
+        long viewerId = await factory.SeedViewerAsync();
+        // Round-trip: own 1 → destruct 1 → Count=0 row remains → protect succeeds
+        await factory.SeedOwnedCardAsync(viewerId, cardId: 10001001L, count: 1, dustReward: 50);
+        using var setup = factory.Services.CreateScope();
+        var setupRepo = setup.ServiceProvider.GetRequiredService<ICardInventoryRepository>();
+        var destruct = await setupRepo.DestructCards(viewerId, new Dictionary<long, int> { { 10001001L, 1 } });
+        Assert.That(destruct.IsSuccess, Is.True, "setup precondition: destruct-to-zero");
+
+        using var scope = factory.Services.CreateScope();
+        var repo = scope.ServiceProvider.GetRequiredService<ICardInventoryRepository>();
+        var outcome = await repo.SetProtected(viewerId, 10001001L, isProtected: true);
+        Assert.That(outcome.IsSuccess, Is.True);
+
+        var db = scope.ServiceProvider.GetRequiredService<SVSimDbContext>();
+        var viewer = await db.Viewers.Include(v => v.Cards).ThenInclude(c => c.Card).FirstAsync(v => v.Id == viewerId);
+        var owned = viewer.Cards.First(c => c.Card.Id == 10001001L);
+        Assert.That(owned.Count, Is.EqualTo(0));
+        Assert.That(owned.IsProtected, Is.True, "protect on zero-count row must persist");
+    }
+
+    [Test]
+    public async Task SetProtected_unknown_card_returns_error()
+    {
+        using var factory = new SVSimTestFactory();
+        long viewerId = await factory.SeedViewerAsync();
+        // No OwnedCardEntry row at all
+
+        using var scope = factory.Services.CreateScope();
+        var repo = scope.ServiceProvider.GetRequiredService<ICardInventoryRepository>();
+
+        var outcome = await repo.SetProtected(viewerId, 99_999_999L, isProtected: true);
+        Assert.That(outcome.IsSuccess, Is.False);
+        Assert.That(outcome.Error, Is.EqualTo(ProtectError.UnknownCard));
+    }
 }