fix(sitecallaudit): time-sliced terminal purge replaces the single year-scale DELETE (plan R2-04 T11)

src/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase/Repositories/SiteCallAuditRepository.cs

@@ -246,9 +246,29 @@ OPTION (RECOMPILE);";
     /// <inheritdoc />
     public async Task<int> PurgeTerminalAsync(DateTime olderThanUtc, CancellationToken ct = default)
     {
-        return await _context.Database.ExecuteSqlInterpolatedAsync(
-            $"DELETE FROM dbo.SiteCalls WHERE TerminalAtUtc IS NOT NULL AND TerminalAtUtc < {olderThanUtc};",
-            ct);
+        // Time-sliced batches (arch-review 04 round 2, R6 — the one maintenance DELETE
+        // that missed round 1's batching pass): each DELETE covers at most one DAY of
+        // terminal rows, capping the lock/log footprint per statement. Steady state
+        // (daily purge, 365-day retention) is a single slice; only catch-up after an
+        // outage runs several. One-day (not one-hour) slices are proportionate to
+        // SiteCalls volume, which is far below KpiSample's. The MIN() anchor and the
+        // DELETE predicate both seek IX_SiteCalls_Terminal (filtered IS NOT NULL).
+        var total = 0;
+        var floor = await _context.SiteCalls
+            .Where(s => s.TerminalAtUtc != null && s.TerminalAtUtc < olderThanUtc)
+            .MinAsync(s => s.TerminalAtUtc, ct);
+        while (floor is not null && floor < olderThanUtc)
+        {
+            var ceiling = floor.Value.AddDays(1) < olderThanUtc ? floor.Value.AddDays(1) : olderThanUtc;
+            total += await _context.Database.ExecuteSqlInterpolatedAsync(
+                $"DELETE FROM dbo.SiteCalls WHERE TerminalAtUtc IS NOT NULL AND TerminalAtUtc < {ceiling};",
+                ct);
+            floor = await _context.SiteCalls
+                .Where(s => s.TerminalAtUtc != null && s.TerminalAtUtc < olderThanUtc)
+                .MinAsync(s => s.TerminalAtUtc, ct);
+        }
+
+        return total;
     }
 
     // Terminal status string literals for the interval-throughput KPIs. The