import_viewer: fix counter upsert race + add explicit slot field

Pre-materialize ViewerEventCounters before the mission loop so in-flight
Adds are visible to subsequent iterations sharing the same (EventKey, Period);
add optional ImportMission.Slot field so callers can supply weekly slot identity
(2 or 3) rather than relying on the LotType-derived default of 1.

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

SVSim.UnitTests/Controllers/AdminControllerTests.cs

@@ -585,4 +585,96 @@ public class AdminControllerTests
         Assert.That(verifyDb3.ViewerMissions.Count(m => m.MissionCatalogId == 9002), Is.EqualTo(1));
         Assert.That(verifyDb3.ViewerEventCounters.Any(), Is.False);
     }
+
+    [Test]
+    public async Task ImportViewer_Missions_TwoMissionsSharingEventType_SingleCounterUpsert()
+    {
+        // Two weekly missions (LotType=2) share the same EventType — same (EventKey, WeekKey)
+        // period — but occupy different slots (1 and 2 via explicit slot override) so the slot
+        // unique-index is satisfied. Without the pre-materialized counterCache the second DB read
+        // won't see the first mission's pending Add → duplicate insert / unique-constraint failure.
+        // With the fix both missions upsert the SAME counter, resulting in exactly one row.
+        using var factory = new SVSimTestFactory();
+        using (var seedScope = factory.Services.CreateScope())
+        {
+            var seedDb = seedScope.ServiceProvider.GetRequiredService<SVSimDbContext>();
+            seedDb.MissionCatalog.AddRange(
+                new MissionCatalogEntry { Id = 9003, LotType = 2, EventType = "battle_win_total", EventArg = null },
+                new MissionCatalogEntry { Id = 9004, LotType = 2, EventType = "battle_win_total", EventArg = null });
+            await seedDb.SaveChangesAsync();
+        }
+        var client = factory.CreateClient();
+        ulong steamId = 70000000000000005UL;
+
+        var resp = await client.PostAsJsonAsync("/admin/import_viewer", new ImportViewerRequest
+        {
+            SteamId = steamId,
+            Missions = new List<ImportMission>
+            {
+                new() { MissionId = 9003, MissionStatus = 1, TotalCount = 10, Slot = 1 },
+                new() { MissionId = 9004, MissionStatus = 1, TotalCount = 10, Slot = 2 },
+            }
+        });
+        resp.EnsureSuccessStatusCode();
+        var body = await resp.Content.ReadFromJsonAsync<ImportViewerResponse>(JsonOptions);
+        Assert.That(body!.SkippedMissionCount, Is.EqualTo(0));
+        Assert.That(body.SkippedMissionCounterCount, Is.EqualTo(0));
+
+        using var verifyScope = factory.Services.CreateScope();
+        var verifyDb = verifyScope.ServiceProvider.GetRequiredService<SVSimDbContext>();
+        var viewerId = await verifyDb.Viewers
+            .Where(v => v.SocialAccountConnections
+                .Any(s => s.AccountType == SocialAccountType.Steam && s.AccountId == steamId))
+            .Select(v => v.Id).SingleAsync();
+
+        // Must be exactly ONE counter row for (EventKey="battle_win_total"), not two.
+        Assert.That(
+            verifyDb.ViewerEventCounters.Count(c => c.ViewerId == viewerId && c.EventKey == "battle_win_total"),
+            Is.EqualTo(1));
+        Assert.That(
+            verifyDb.ViewerEventCounters
+                .Single(c => c.ViewerId == viewerId && c.EventKey == "battle_win_total").Count,
+            Is.EqualTo(10));
+    }
+
+    [Test]
+    public async Task ImportViewer_Missions_ExplicitSlotRoundTrips()
+    {
+        // A weekly catalog mission (LotType=2) posted with an explicit slot=3 must persist Slot=3,
+        // not fall back to the LotType-derived default of 1.
+        using var factory = new SVSimTestFactory();
+        using (var seedScope = factory.Services.CreateScope())
+        {
+            var seedDb = seedScope.ServiceProvider.GetRequiredService<SVSimDbContext>();
+            seedDb.MissionCatalog.Add(new MissionCatalogEntry
+            {
+                Id = 9005, LotType = 2 /* weekly */,
+                EventType = null, EventArg = null
+            });
+            await seedDb.SaveChangesAsync();
+        }
+        var client = factory.CreateClient();
+        ulong steamId = 70000000000000006UL;
+
+        var resp = await client.PostAsJsonAsync("/admin/import_viewer", new ImportViewerRequest
+        {
+            SteamId = steamId,
+            Missions = new List<ImportMission>
+            {
+                new() { MissionId = 9005, MissionStatus = 1, TotalCount = 0, Slot = 3 }
+            }
+        });
+        resp.EnsureSuccessStatusCode();
+
+        using var verifyScope = factory.Services.CreateScope();
+        var verifyDb = verifyScope.ServiceProvider.GetRequiredService<SVSimDbContext>();
+        var viewerId = await verifyDb.Viewers
+            .Where(v => v.SocialAccountConnections
+                .Any(s => s.AccountType == SocialAccountType.Steam && s.AccountId == steamId))
+            .Select(v => v.Id).SingleAsync();
+
+        var mission = await verifyDb.ViewerMissions
+            .SingleAsync(m => m.ViewerId == viewerId && m.MissionCatalogId == 9005);
+        Assert.That(mission.Slot, Is.EqualTo(3));
+    }
 }