src/Bifrost.Web/Features/Motions/MotionGovernanceService.cs

@@ -126,7 +126,21 @@ public sealed class MotionGovernanceService(
             ? $"Closed with {votesFor:0.##} for and {votesAgainst:0.##} against at a {motion.ApprovalThreshold:P0} threshold."
             : "Closed without decisive votes.";
 
-        await dbContext.SaveChangesAsync(cancellationToken);
+        try
+        {
+            await dbContext.SaveChangesAsync(cancellationToken);
+        }
+        catch (DbUpdateConcurrencyException error)
+        {
+            // Status is a concurrency token: another closer won. Adopt its result and record nothing a second time.
+            foreach (var entry in error.Entries)
+            {
+                await entry.ReloadAsync(cancellationToken);
+            }
+
+            return;
+        }
+
         await auditTrailService.RecordAsync(
             actorUser.Id,
             nameof(Motion),

tests/Bifrost.Web.Tests/StandardMotionCloseTests.cs

@@ -0,0 +1,49 @@
+using Bifrost.Web.Data;
+using Bifrost.Web.Domain;
+using Bifrost.Web.Features.Motions;
+using Bifrost.Web.Features.Shared;
+using Microsoft.EntityFrameworkCore;
+
+namespace Bifrost.Web.Tests;
+
+public sealed class StandardMotionCloseTests
+{
+    private static readonly DateTimeOffset T0 = new(2026, 11, 10, 12, 0, 0, TimeSpan.Zero);
+
+    private sealed class Clock(DateTimeOffset start) : TimeProvider
+    {
+        public override DateTimeOffset GetUtcNow() => start;
+    }
+
+    [Fact]
+    public async Task A_second_simultaneous_close_adopts_the_winners_close_and_records_nothing_more()
+    {
+        var clock = new Clock(T0);
+        var name = $"standard-close-race-{Guid.NewGuid():N}";
+        BifrostDbContext NewDb() => new(new DbContextOptionsBuilder<BifrostDbContext>().UseInMemoryDatabase(name).Options);
+        MotionGovernanceService NewService(BifrostDbContext db) => new(db, new AuditTrailService(db, clock), clock);
+
+        await using var seed = NewDb();
+        var user = new UserAccount { DisplayName = "Mod", GitHubLogin = "mod", BifrostIdentity = "mod", NormalizedBifrostIdentity = "MOD", NormalizedGitHubLogin = "MOD" };
+        user.Membership = new Membership { UserAccountId = user.Id, Status = MembershipStatus.Active, CanModerateMotions = true };
+        seed.UserAccounts.Add(user);
+        await seed.SaveChangesAsync();
+        var actor = new CurrentBifrostActor(true, user);
+        var motion = await NewService(seed).CreateMotionAsync(
+            actor,
+            new CreateMotionCommand(MotionScope.Management, null, MotionCategory.Features, "Race", "Two closers.", T0.AddDays(1)),
+            default);
+
+        await using var first = NewDb();
+        await using var second = NewDb();
+        _ = await second.Motions.ToListAsync(); // second now holds a stale, still-Open copy
+
+        await NewService(first).CloseMotionAsync(actor, motion.Id, default);
+        await NewService(second).CloseMotionAsync(actor, motion.Id, default); // the Status token refuses this write
+
+        await using var check = NewDb();
+        var row = await check.Motions.SingleAsync();
+        Assert.Equal(MotionStatus.Closed, row.Status);
+        Assert.Equal(1, await check.AuditEvents.CountAsync(x => x.Action == "motion.closed"));
+    }
+}