diff --git a/src/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase/Repositories/KpiHistoryRepository.cs b/src/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase/Repositories/KpiHistoryRepository.cs
index d772b543..2f6fd26a 100644
--- a/src/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase/Repositories/KpiHistoryRepository.cs
+++ b/src/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase/Repositories/KpiHistoryRepository.cs
@@ -101,8 +101,14 @@ public sealed class KpiHistoryRepository : IKpiHistoryRepository
         // fetch it and group IN MEMORY. This deliberately avoids provider-specific
         // DATEADD/DATEPART hour-truncation translation (SQLite in tests, SQL Server in prod),
         // keeping the hour-bucket arithmetic identical across providers and trivially correct.
+        // Projected, untracked fetch: the fold only reads these six fields and never
+        // mutates a KpiSample. A tracked ToListAsync registered ~5k-90k read-only
+        // entities in the change tracker per healthy 3h fold — all re-scanned by
+        // DetectChanges on the final SaveChanges (arch-review 04 round 2, R2). A
+        // projection is inherently untracked and materializes no entity at all.
         var samples = await _context.KpiSamples
             .Where(s => s.CapturedAtUtc >= from && s.CapturedAtUtc < to)
+            .Select(s => new FoldSample(s.Source, s.Metric, s.Scope, s.ScopeKey, s.CapturedAtUtc, s.Value))
             .ToListAsync(cancellationToken);
         if (samples.Count == 0)
         {
@@ -212,4 +218,8 @@ public sealed class KpiHistoryRepository : IKpiHistoryRepository
     /// <summary>In-memory grouping key: one KPI series (four-tuple) within one UTC hour.</summary>
     private readonly record struct SeriesHourKey(
         string Source, string Metric, string Scope, string? ScopeKey, DateTime HourStartUtc);
+
+    /// <summary>Narrow, untracked projection of one KpiSample row for the fold (R2).</summary>
+    private readonly record struct FoldSample(
+        string Source, string Metric, string Scope, string? ScopeKey, DateTime CapturedAtUtc, double Value);
 }
diff --git a/tests/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase.Tests/Repositories/KpiHistoryRepositoryTests.cs b/tests/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase.Tests/Repositories/KpiHistoryRepositoryTests.cs
index 68822e4e..4aa216f8 100644
--- a/tests/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase.Tests/Repositories/KpiHistoryRepositoryTests.cs
+++ b/tests/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase.Tests/Repositories/KpiHistoryRepositoryTests.cs
@@ -386,6 +386,26 @@ public class KpiHistoryRepositoryTests
         Assert.Equal(new[] { 3d, 4d }, remaining.Select(p => p.Value).ToArray());
     }
 
+    [Fact]
+    public async Task FoldHourlyRollups_DoesNotTrack_KpiSampleEntities()
+    {
+        await using var ctx = NewContext();
+        var repo = new KpiHistoryRepository(ctx);
+        await repo.RecordSamplesAsync(new[]
+        {
+            Sample("NotificationOutbox", "queueDepth", "Global", null, 5, Base.AddMinutes(10)),
+            Sample("NotificationOutbox", "queueDepth", "Global", null, 7, Base.AddMinutes(50)),
+        });
+        ctx.ChangeTracker.Clear(); // isolate the fold's tracking behavior from the seed
+
+        await repo.FoldHourlyRollupsAsync(Base, Base.AddHours(1));
+
+        // The fold READS samples and WRITES rollups; the read must not register
+        // thousands of read-only KpiSample entries for DetectChanges to re-scan
+        // (arch-review 04 round 2, R2).
+        Assert.Empty(ctx.ChangeTracker.Entries<KpiSample>());
+    }
+
     // Local mirror of the repo's private hour-truncation, for cutoff assertions.
     private static DateTime TruncateHour(DateTime utc) =>
         new(utc.Year, utc.Month, utc.Day, utc.Hour, 0, 0, DateTimeKind.Utc);