perf(backend): project index scans + bound AppInstall reads to window

Two classes of read-efficiency fixes on hot/aggregation paths. No response
shape or value changes — DTOs untouched, all 2541 backend tests pass.

P2 — select projections on full-mirror SessionsIndex scans (bandwidth only):
- GetMetricsSummaryAsync: cross-partition status tally now projects
  [PartitionKey, Status] instead of the ~40-column mirror row (incl. the
  large FailureSnapshotJson) -> ~10-20x less transfer.
- QuickSearchSessionsAsync: typeahead scan projects only the matched fields
  (+ RowKey for the SessionId fallback) instead of the full row, for up to
  QuickSearchMaxScannedRows rows per request.

P3 — push the existing sinceUtc window floor server-side at 8 AppInstall
call sites across 5 files (previously each dematerialized the whole table /
partition and filtered to the window in memory):
- UsageMetricsService (global + tenant): now.AddDays(-days)
- MaintenanceService.Aggregation (global + tenant, per aggregated day): targetDate
- SlaBreachEvaluationService (current ISO week): now.AddDays(-8) margin
- SlaMetricsService: startDate (matches the in-memory lower bound exactly)
- Get(Global)GeographicLocationSessionsFunction: cutoff

Each floor equals the session-window floor the apps are joined against
(app.StartedAt >= session.StartedAt >= floor), so results are unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/Backend/AutopilotMonitor.Functions/Functions/Metrics/GetGeographicLocationSessionsFunction.cs

@@ -69,7 +69,8 @@ namespace AutopilotMonitor.Functions.Functions.Metrics
                     ? FilterSessionsByLocation(sessions, locationKey, groupBy)
                     : FilterSessionsByFields(sessions, country!, query["region"], query["city"]);
 
-                var appSummaries = await _metricsRepo.GetAppInstallSummariesByTenantAsync(tenantId);
+                // Same window as the sessions above (cutoff); BuildRows joins apps to those sessions.
+                var appSummaries = await _metricsRepo.GetAppInstallSummariesByTenantAsync(tenantId, cutoff);
                 var rows = BuildRows(filtered, appSummaries);
 
                 var response = req.CreateResponse(HttpStatusCode.OK);

src/Backend/AutopilotMonitor.Functions/Functions/Metrics/GetGlobalGeographicLocationSessionsFunction.cs

@@ -67,9 +67,10 @@ namespace AutopilotMonitor.Functions.Functions.Metrics
                     ? GetGeographicLocationSessionsFunction.FilterSessionsByLocation(sessions, locationKey, groupBy)
                     : GetGeographicLocationSessionsFunction.FilterSessionsByFields(sessions, country!, query["region"], query["city"]);
 
+                // Same window as the sessions above (cutoff); BuildRows joins apps to those sessions.
                 var appSummaries = string.IsNullOrEmpty(filterTenantId)
-                    ? await _metricsRepo.GetAllAppInstallSummariesAsync()
+                    ? await _metricsRepo.GetAllAppInstallSummariesAsync(cutoff)
-                    : await _metricsRepo.GetAppInstallSummariesByTenantAsync(filterTenantId);
+                    : await _metricsRepo.GetAppInstallSummariesByTenantAsync(filterTenantId, cutoff);
                 var rows = GetGeographicLocationSessionsFunction.BuildRows(filtered, appSummaries);
 
                 var response = req.CreateResponse(HttpStatusCode.OK);

src/Backend/AutopilotMonitor.Functions/Services/MaintenanceService.Aggregation.cs

@@ -139,10 +139,13 @@ namespace AutopilotMonitor.Functions.Services
             // App metrics: count apps per session from AppInstallSummaries table
             var sessionIdSet = new HashSet<string>(sessions.Select(s => s.SessionId));
             List<AppInstallSummary> appSummaries;
+            // Bound the AppInstall scan to this snapshot's day. The session set is already
+            // [targetDate, targetDate+1) and apps install during their session (StartedAt >= targetDate),
+            // so relevantApps is unchanged; without sinceUtc this scanned the whole table per aggregated day.
             if (tenantId == "global")
-                appSummaries = await _metricsRepo.GetAllAppInstallSummariesAsync();
+                appSummaries = await _metricsRepo.GetAllAppInstallSummariesAsync(targetDate);
             else
-                appSummaries = await _metricsRepo.GetAppInstallSummariesByTenantAsync(tenantId);
+                appSummaries = await _metricsRepo.GetAppInstallSummariesByTenantAsync(tenantId, targetDate);
 
             var relevantApps = appSummaries.Where(a => sessionIdSet.Contains(a.SessionId)).ToList();
             var appsPerSession = relevantApps.GroupBy(a => a.SessionId).Select(g => g.Count()).ToList();

src/Backend/AutopilotMonitor.Functions/Services/SlaBreachEvaluationService.cs

@@ -186,7 +186,10 @@ namespace AutopilotMonitor.Functions.Services
             if (config.SlaNotifyOnAppInstallBreach && config.SlaTargetAppInstallSuccessRate.HasValue)
             {
                 var currentWeekKey = SlaMetricsService.GetIsoWeekKey(now);
-                var raw = await _metricsRepo.GetAppInstallSummariesByTenantAsync(config.TenantId);
+                // Bound to a safe margin before the current ISO week (an ISO week spans <=7 days, so
+                // now-8d never excludes a current-week row). The exact week match happens in-memory
+                // below; this just stops the query from scanning the tenant's entire history every 2h.
+                var raw = await _metricsRepo.GetAppInstallSummariesByTenantAsync(config.TenantId, now.AddDays(-8));
                 appInstalls = raw
                     .Where(a => (a.Status == "Succeeded" || a.Status == "Failed")
                                 && SlaMetricsService.GetIsoWeekKey(a.StartedAt) == currentWeekKey)

src/Backend/AutopilotMonitor.Functions/Services/SlaMetricsService.cs

@@ -125,7 +125,9 @@ namespace AutopilotMonitor.Functions.Services
             List<AppInstallSummary>? appInstalls = null;
             if (config?.SlaTargetAppInstallSuccessRate != null)
             {
-                appInstalls = await _metricsRepo.GetAppInstallSummariesByTenantAsync(tenantId);
+                // Push the window's lower bound server-side (startDate); the in-memory filter below
+                // still applies the upper bound. Without sinceUtc this read the tenant's full history.
+                appInstalls = await _metricsRepo.GetAppInstallSummariesByTenantAsync(tenantId, startDate);
                 // Filter to the time window
                 appInstalls = appInstalls
                     .Where(a => a.StartedAt >= startDate && a.StartedAt <= endDate)

src/Backend/AutopilotMonitor.Functions/Services/TableStorageService.AgentApi.cs

@@ -338,7 +338,11 @@ namespace AutopilotMonitor.Functions.Services
                 : windowBound;
 
             var scannedRows = 0;
-            await foreach (var entity in indexTableClient.QueryAsync<TableEntity>(filter: filter))
+            // Project to only the typeahead-matched fields (+ RowKey for the SessionId fallback at
+            // ExtractSessionIdFromIndexRowKey). Avoids pulling the full ~40-column SessionsIndex
+            // mirror for up to QuickSearchMaxScannedRows rows on every keystroke-driven request.
+            await foreach (var entity in indexTableClient.QueryAsync<TableEntity>(
+                filter: filter, select: new[] { "RowKey", "SessionId", "SerialNumber", "DeviceName", "Status", "StartedAt" }))
             {
                 if (++scannedRows > QuickSearchMaxScannedRows)
                     break;
@@ -1261,7 +1265,11 @@ namespace AutopilotMonitor.Functions.Services
             // longer vanish from the summary). See SessionStatusBuckets in MetricsMath.cs.
             var groups = new Dictionary<string, SessionStatusBuckets>(StringComparer.OrdinalIgnoreCase);
 
-            await foreach (var entity in indexTableClient.QueryAsync<TableEntity>(filter: oDataFilter))
+            // Project to the two columns the tally consumes. The SessionsIndex row is a full
+            // ~40-column mirror (incl. the large FailureSnapshotJson), so reading it whole for a
+            // status count multiplied transfer ~10-20x for nothing on this cross-partition scan.
+            await foreach (var entity in indexTableClient.QueryAsync<TableEntity>(
+                filter: oDataFilter, select: new[] { "PartitionKey", "Status" }))
             {
                 var pk = entity.PartitionKey;
                 var statusStr = entity.GetString("Status") ?? "InProgress";

src/Backend/AutopilotMonitor.Functions/Services/UsageMetricsService.cs

@@ -217,7 +217,11 @@ namespace AutopilotMonitor.Functions.Services
             };
 
             // App & Script Metrics
-            var allAppSummaries = await _metricsRepo.GetAllAppInstallSummariesAsync();
+            // Bound the AppInstall scan to the same window as the sessions above — relevantApps is
+            // filtered to sessionIdSet anyway, and an app installs during its session so its StartedAt
+            // is >= the session's. Without sinceUtc this dematerialized the entire AppInstallSummaries
+            // table on every cache miss just to discard everything outside the window.
+            var allAppSummaries = await _metricsRepo.GetAllAppInstallSummariesAsync(DateTime.UtcNow.AddDays(-days));
             var sessionIdSet = new HashSet<string>(allSessions.Select(s => s.SessionId));
             var relevantApps = allAppSummaries.Where(a => sessionIdSet.Contains(a.SessionId)).ToList();
             var appsPerSessionList = relevantApps.GroupBy(a => a.SessionId).Select(g => g.Count()).ToList();
@@ -366,7 +370,8 @@ namespace AutopilotMonitor.Functions.Services
             };
 
             // App & Script Metrics
-            var tenantAppSummaries = await _metricsRepo.GetAppInstallSummariesByTenantAsync(tenantId);
+            // Bound to the window (see ComputeUsageMetricsInternalAsync) — joined to tenantSessionIdSet below.
+            var tenantAppSummaries = await _metricsRepo.GetAppInstallSummariesByTenantAsync(tenantId, DateTime.UtcNow.AddDays(-days));
             var tenantSessionIdSet = new HashSet<string>(tenantSessions.Select(s => s.SessionId));
             var relevantTenantApps = tenantAppSummaries.Where(a => tenantSessionIdSet.Contains(a.SessionId)).ToList();
             var tenantAppsPerSession = relevantTenantApps.GroupBy(a => a.SessionId).Select(g => g.Count()).ToList();