feat(friend): implement single-target write methods on FriendService

SendApplyAsync, ApproveApplyAsync, RejectApplyAsync, CancelApplyAsync,
RejectFriendAsync all implemented. 11 new tests appended; all 23 friend
tests pass, full suite 1182/1182 green.

SVSim.UnitTests/Services/FriendServiceTests.cs

@@ -293,4 +293,246 @@ public class FriendServiceTests
             Assert.That(result, Is.Null);
         }
     }
+
+    [Test]
+    public async Task SendApplyAsync_creates_apply_row()
+    {
+        using var factory = new SVSimTestFactory();
+        long sender = await SeedViewer(factory, 76_561_198_000_001_001UL);
+        long target = await SeedViewer(factory, 76_561_198_000_001_002UL);
+
+        var svc = Service(factory, out var scope);
+        using (scope) await svc.SendApplyAsync(sender, (int)target, default);
+
+        using var verifyScope = factory.Services.CreateScope();
+        var ctx = Ctx(verifyScope);
+        var applies = await ctx.ViewerFriendApplies.AsNoTracking().Where(a => a.FromViewerId == sender).ToListAsync();
+        Assert.That(applies, Has.Count.EqualTo(1));
+        Assert.That(applies[0].ToViewerId, Is.EqualTo(target));
+    }
+
+    [Test]
+    public async Task SendApplyAsync_no_op_for_self()
+    {
+        using var factory = new SVSimTestFactory();
+        long sender = await SeedViewer(factory, 76_561_198_000_001_003UL);
+
+        var svc = Service(factory, out var scope);
+        using (scope) await svc.SendApplyAsync(sender, (int)sender, default);
+
+        using var verifyScope = factory.Services.CreateScope();
+        var count = await Ctx(verifyScope).ViewerFriendApplies.CountAsync();
+        Assert.That(count, Is.EqualTo(0));
+    }
+
+    [Test]
+    public async Task SendApplyAsync_no_op_for_unknown_target()
+    {
+        using var factory = new SVSimTestFactory();
+        long sender = await SeedViewer(factory, 76_561_198_000_001_004UL);
+
+        var svc = Service(factory, out var scope);
+        using (scope) await svc.SendApplyAsync(sender, 999_999_999, default);
+
+        using var verifyScope = factory.Services.CreateScope();
+        var count = await Ctx(verifyScope).ViewerFriendApplies.CountAsync();
+        Assert.That(count, Is.EqualTo(0));
+    }
+
+    [Test]
+    public async Task SendApplyAsync_no_op_when_already_friends()
+    {
+        using var factory = new SVSimTestFactory();
+        long me = await SeedViewer(factory, 76_561_198_000_001_005UL);
+        long friend = await SeedViewer(factory, 76_561_198_000_001_006UL);
+
+        using (var scope = factory.Services.CreateScope())
+        {
+            var ctx = Ctx(scope);
+            ctx.ViewerFriends.Add(new ViewerFriend { OwnerViewerId = me, FriendViewerId = friend, CreatedAt = DateTime.UtcNow });
+            await ctx.SaveChangesAsync();
+        }
+
+        var svc = Service(factory, out var scope2);
+        using (scope2) await svc.SendApplyAsync(me, (int)friend, default);
+
+        using var verifyScope = factory.Services.CreateScope();
+        var count = await Ctx(verifyScope).ViewerFriendApplies.CountAsync();
+        Assert.That(count, Is.EqualTo(0));
+    }
+
+    [Test]
+    public async Task SendApplyAsync_no_op_when_already_pending()
+    {
+        using var factory = new SVSimTestFactory();
+        long sender = await SeedViewer(factory, 76_561_198_000_001_007UL);
+        long target = await SeedViewer(factory, 76_561_198_000_001_008UL);
+
+        using (var scope = factory.Services.CreateScope())
+        {
+            var ctx = Ctx(scope);
+            ctx.ViewerFriendApplies.Add(new ViewerFriendApply { FromViewerId = sender, ToViewerId = target, CreatedAt = DateTime.UtcNow });
+            await ctx.SaveChangesAsync();
+        }
+
+        var svc = Service(factory, out var scope2);
+        using (scope2) await svc.SendApplyAsync(sender, (int)target, default);
+
+        using var verifyScope = factory.Services.CreateScope();
+        var count = await Ctx(verifyScope).ViewerFriendApplies.CountAsync();
+        Assert.That(count, Is.EqualTo(1), "Pre-existing apply must not be duplicated");
+    }
+
+    [Test]
+    public async Task ApproveApplyAsync_creates_two_friend_rows_and_deletes_apply()
+    {
+        using var factory = new SVSimTestFactory();
+        long target = await SeedViewer(factory, 76_561_198_000_001_009UL);
+        long sender = await SeedViewer(factory, 76_561_198_000_001_010UL);
+
+        int applyId;
+        using (var scope = factory.Services.CreateScope())
+        {
+            var ctx = Ctx(scope);
+            var apply = new ViewerFriendApply { FromViewerId = sender, ToViewerId = target, CreatedAt = DateTime.UtcNow };
+            ctx.ViewerFriendApplies.Add(apply);
+            await ctx.SaveChangesAsync();
+            applyId = apply.Id;
+        }
+
+        var svc = Service(factory, out var scope2);
+        using (scope2) await svc.ApproveApplyAsync(target, applyId, default);
+
+        using var verifyScope = factory.Services.CreateScope();
+        var ctx2 = Ctx(verifyScope);
+        var friends = await ctx2.ViewerFriends.AsNoTracking().ToListAsync();
+        Assert.That(friends, Has.Count.EqualTo(2));
+        Assert.That(friends.Any(f => f.OwnerViewerId == target && f.FriendViewerId == sender));
+        Assert.That(friends.Any(f => f.OwnerViewerId == sender && f.FriendViewerId == target));
+        Assert.That(await ctx2.ViewerFriendApplies.CountAsync(), Is.EqualTo(0));
+    }
+
+    [Test]
+    public async Task ApproveApplyAsync_cleans_reverse_direction_apply_if_present()
+    {
+        using var factory = new SVSimTestFactory();
+        long target = await SeedViewer(factory, 76_561_198_000_001_011UL);
+        long sender = await SeedViewer(factory, 76_561_198_000_001_012UL);
+
+        int applyId;
+        using (var scope = factory.Services.CreateScope())
+        {
+            var ctx = Ctx(scope);
+            var a = new ViewerFriendApply { FromViewerId = sender, ToViewerId = target, CreatedAt = DateTime.UtcNow };
+            // The reverse-direction apply that should get cleaned.
+            var b = new ViewerFriendApply { FromViewerId = target, ToViewerId = sender, CreatedAt = DateTime.UtcNow };
+            ctx.ViewerFriendApplies.AddRange(a, b);
+            await ctx.SaveChangesAsync();
+            applyId = a.Id;
+        }
+
+        var svc = Service(factory, out var scope2);
+        using (scope2) await svc.ApproveApplyAsync(target, applyId, default);
+
+        using var verifyScope = factory.Services.CreateScope();
+        Assert.That(await Ctx(verifyScope).ViewerFriendApplies.CountAsync(), Is.EqualTo(0),
+            "Both directions' applies must be cleaned");
+    }
+
+    [Test]
+    public async Task ApproveApplyAsync_no_op_when_apply_not_addressed_to_caller()
+    {
+        using var factory = new SVSimTestFactory();
+        long imposter = await SeedViewer(factory, 76_561_198_000_001_013UL);
+        long target = await SeedViewer(factory, 76_561_198_000_001_014UL);
+        long sender = await SeedViewer(factory, 76_561_198_000_001_015UL);
+
+        int applyId;
+        using (var scope = factory.Services.CreateScope())
+        {
+            var ctx = Ctx(scope);
+            var apply = new ViewerFriendApply { FromViewerId = sender, ToViewerId = target, CreatedAt = DateTime.UtcNow };
+            ctx.ViewerFriendApplies.Add(apply);
+            await ctx.SaveChangesAsync();
+            applyId = apply.Id;
+        }
+
+        var svc = Service(factory, out var scope2);
+        using (scope2) await svc.ApproveApplyAsync(imposter, applyId, default);
+
+        using var verifyScope = factory.Services.CreateScope();
+        var ctx2 = Ctx(verifyScope);
+        Assert.That(await ctx2.ViewerFriendApplies.CountAsync(), Is.EqualTo(1), "Apply must survive");
+        Assert.That(await ctx2.ViewerFriends.CountAsync(), Is.EqualTo(0), "No friendship created");
+    }
+
+    [Test]
+    public async Task RejectApplyAsync_deletes_apply_only_for_correct_recipient()
+    {
+        using var factory = new SVSimTestFactory();
+        long target = await SeedViewer(factory, 76_561_198_000_001_016UL);
+        long sender = await SeedViewer(factory, 76_561_198_000_001_017UL);
+
+        int applyId;
+        using (var scope = factory.Services.CreateScope())
+        {
+            var ctx = Ctx(scope);
+            var apply = new ViewerFriendApply { FromViewerId = sender, ToViewerId = target, CreatedAt = DateTime.UtcNow };
+            ctx.ViewerFriendApplies.Add(apply);
+            await ctx.SaveChangesAsync();
+            applyId = apply.Id;
+        }
+
+        var svc = Service(factory, out var scope2);
+        using (scope2) await svc.RejectApplyAsync(target, applyId, default);
+
+        using var verifyScope = factory.Services.CreateScope();
+        Assert.That(await Ctx(verifyScope).ViewerFriendApplies.CountAsync(), Is.EqualTo(0));
+    }
+
+    [Test]
+    public async Task CancelApplyAsync_deletes_apply_only_for_correct_sender()
+    {
+        using var factory = new SVSimTestFactory();
+        long sender = await SeedViewer(factory, 76_561_198_000_001_018UL);
+        long target = await SeedViewer(factory, 76_561_198_000_001_019UL);
+
+        int applyId;
+        using (var scope = factory.Services.CreateScope())
+        {
+            var ctx = Ctx(scope);
+            var apply = new ViewerFriendApply { FromViewerId = sender, ToViewerId = target, CreatedAt = DateTime.UtcNow };
+            ctx.ViewerFriendApplies.Add(apply);
+            await ctx.SaveChangesAsync();
+            applyId = apply.Id;
+        }
+
+        var svc = Service(factory, out var scope2);
+        using (scope2) await svc.CancelApplyAsync(sender, applyId, default);
+
+        using var verifyScope = factory.Services.CreateScope();
+        Assert.That(await Ctx(verifyScope).ViewerFriendApplies.CountAsync(), Is.EqualTo(0));
+    }
+
+    [Test]
+    public async Task RejectFriendAsync_deletes_both_directions()
+    {
+        using var factory = new SVSimTestFactory();
+        long me = await SeedViewer(factory, 76_561_198_000_001_020UL);
+        long other = await SeedViewer(factory, 76_561_198_000_001_021UL);
+
+        using (var scope = factory.Services.CreateScope())
+        {
+            var ctx = Ctx(scope);
+            ctx.ViewerFriends.Add(new ViewerFriend { OwnerViewerId = me, FriendViewerId = other, CreatedAt = DateTime.UtcNow });
+            ctx.ViewerFriends.Add(new ViewerFriend { OwnerViewerId = other, FriendViewerId = me, CreatedAt = DateTime.UtcNow });
+            await ctx.SaveChangesAsync();
+        }
+
+        var svc = Service(factory, out var scope2);
+        using (scope2) await svc.RejectFriendAsync(me, (int)other, default);
+
+        using var verifyScope = factory.Services.CreateScope();
+        Assert.That(await Ctx(verifyScope).ViewerFriends.CountAsync(), Is.EqualTo(0));
+    }
 }