feat(friend): bulk apply ops + IPlayedTogetherWriter with retention cap

Implements RejectAllAppliesAsync, CancelAllAppliesAsync (ExecuteDelete bulk
deletes on incoming/outgoing applies respectively) and RecordAsync (upsert
played-together row with 50-row per-viewer retention eviction). 4 new tests
added; all 1186 tests pass.

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

SVSim.UnitTests/Services/FriendServiceTests.cs

@@ -535,4 +535,108 @@ public class FriendServiceTests
         using var verifyScope = factory.Services.CreateScope();
         Assert.That(await Ctx(verifyScope).ViewerFriends.CountAsync(), Is.EqualTo(0));
     }
+
+    [Test]
+    public async Task RejectAllAppliesAsync_deletes_only_incoming_for_caller()
+    {
+        using var factory = new SVSimTestFactory();
+        long me = await SeedViewer(factory, 76_561_198_000_002_001UL);
+        long other = await SeedViewer(factory, 76_561_198_000_002_002UL);
+
+        using (var scope = factory.Services.CreateScope())
+        {
+            var ctx = Ctx(scope);
+            ctx.ViewerFriendApplies.Add(new ViewerFriendApply { FromViewerId = other, ToViewerId = me, CreatedAt = DateTime.UtcNow });
+            ctx.ViewerFriendApplies.Add(new ViewerFriendApply { FromViewerId = me, ToViewerId = other, CreatedAt = DateTime.UtcNow });
+            await ctx.SaveChangesAsync();
+        }
+
+        var svc = Service(factory, out var scope2);
+        using (scope2) await svc.RejectAllAppliesAsync(me, default);
+
+        using var verifyScope = factory.Services.CreateScope();
+        var remaining = await Ctx(verifyScope).ViewerFriendApplies.AsNoTracking().ToListAsync();
+        Assert.That(remaining, Has.Count.EqualTo(1));
+        Assert.That(remaining[0].FromViewerId, Is.EqualTo(me), "Outgoing must survive");
+    }
+
+    [Test]
+    public async Task CancelAllAppliesAsync_deletes_only_outgoing_for_caller()
+    {
+        using var factory = new SVSimTestFactory();
+        long me = await SeedViewer(factory, 76_561_198_000_002_003UL);
+        long other = await SeedViewer(factory, 76_561_198_000_002_004UL);
+
+        using (var scope = factory.Services.CreateScope())
+        {
+            var ctx = Ctx(scope);
+            ctx.ViewerFriendApplies.Add(new ViewerFriendApply { FromViewerId = me, ToViewerId = other, CreatedAt = DateTime.UtcNow });
+            ctx.ViewerFriendApplies.Add(new ViewerFriendApply { FromViewerId = other, ToViewerId = me, CreatedAt = DateTime.UtcNow });
+            await ctx.SaveChangesAsync();
+        }
+
+        var svc = Service(factory, out var scope2);
+        using (scope2) await svc.CancelAllAppliesAsync(me, default);
+
+        using var verifyScope = factory.Services.CreateScope();
+        var remaining = await Ctx(verifyScope).ViewerFriendApplies.AsNoTracking().ToListAsync();
+        Assert.That(remaining, Has.Count.EqualTo(1));
+        Assert.That(remaining[0].ToViewerId, Is.EqualTo(me), "Incoming must survive");
+    }
+
+    [Test]
+    public async Task RecordAsync_upserts_PlayedAt_for_existing_pair()
+    {
+        using var factory = new SVSimTestFactory();
+        long me = await SeedViewer(factory, 76_561_198_000_002_005UL);
+        long opp = await SeedViewer(factory, 76_561_198_000_002_006UL);
+
+        var ctxFactory = factory.Services;
+        IPlayedTogetherWriter writer;
+        using (var scope = ctxFactory.CreateScope())
+        {
+            writer = scope.ServiceProvider.GetRequiredService<IPlayedTogetherWriter>();
+            await writer.RecordAsync(me, opp, new BattleParticipationContext(1, 2, 3, 4), default);
+        }
+        DateTime firstTimestamp;
+        using (var scope = ctxFactory.CreateScope())
+        {
+            firstTimestamp = (await Ctx(scope).ViewerPlayedTogethers.AsNoTracking()
+                .FirstAsync(p => p.OwnerViewerId == me && p.OpponentViewerId == opp)).PlayedAt;
+        }
+
+        // Wait a tick, record again.
+        await Task.Delay(20);
+        using (var scope = ctxFactory.CreateScope())
+        {
+            writer = scope.ServiceProvider.GetRequiredService<IPlayedTogetherWriter>();
+            await writer.RecordAsync(me, opp, new BattleParticipationContext(5, 6, 7, 8), default);
+        }
+
+        using var verifyScope = ctxFactory.CreateScope();
+        var rows = await Ctx(verifyScope).ViewerPlayedTogethers.AsNoTracking()
+            .Where(p => p.OwnerViewerId == me).ToListAsync();
+        Assert.That(rows, Has.Count.EqualTo(1), "Upsert — no duplicate row");
+        Assert.That(rows[0].PlayedAt, Is.GreaterThan(firstTimestamp));
+        Assert.That(rows[0].PlayedMode, Is.EqualTo(5), "Latest context wins");
+        Assert.That(rows[0].BattleType, Is.EqualTo(6));
+        Assert.That(rows[0].DeckFormat, Is.EqualTo(7));
+        Assert.That(rows[0].TwoPickType, Is.EqualTo(8));
+    }
+
+    [Test]
+    public async Task RecordAsync_no_op_when_owner_equals_opponent()
+    {
+        using var factory = new SVSimTestFactory();
+        long me = await SeedViewer(factory, 76_561_198_000_002_007UL);
+
+        using (var scope = factory.Services.CreateScope())
+        {
+            var writer = scope.ServiceProvider.GetRequiredService<IPlayedTogetherWriter>();
+            await writer.RecordAsync(me, me, new BattleParticipationContext(0, 0, 0, 0), default);
+        }
+
+        using var verifyScope = factory.Services.CreateScope();
+        Assert.That(await Ctx(verifyScope).ViewerPlayedTogethers.CountAsync(), Is.EqualTo(0));
+    }
 }