fix(kpi): untracked projected fold fetch — fold reads no longer flood the change tracker (plan R2-04 T1)

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);
 }