perf(backend): push app-install-summary time window server-side + parallelize session join

The app dashboard and metrics endpoints loaded entire AppInstallSummaries
partitions (tenant scope) or the full table (global scope) and filtered
StartedAt >= cutoff in memory, even for days=30. The device-model join then
issued one serial GetSessionAsync point-read per distinct session.

- Add optional DateTime? sinceUtc to GetAppInstallSummariesByTenantAsync /
  GetAllAppInstallSummariesAsync: when set, a server-side StartedAt ge filter
  scopes the scan so only in-window rows are deserialized/transferred. Default
  null preserves the legacy full scan for callers that need all history.
- AppsAnalyticsHelper.LoadSummariesAsync derives sinceUtc from days; all six
  /api/apps/* functions pass it. The four metrics/app + metrics/geographic
  functions pass their existing cutoff. The in-memory Where stays as the exact
  sub-second trim (the OData filter is second-granular). MCP get_app_install_metrics
  benefits automatically (days already flows through; response shape unchanged).
- Replace the serial session point-read loop with a bounded-concurrency
  (SemaphoreSlim=10) LoadSessionLookupAsync, shared by the analytics and
  sessions builders.

AppInstallSummaries is already bounded by the session-retention cascade
(DeletionManifestBuilder) + tenant offboarding, so no separate table retention
is added. Full Backend suite: 2406 passed / 0 failed.

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

src/Backend/AutopilotMonitor.Functions.Tests/SlaMetricsServiceTests.cs

@@ -32,7 +32,7 @@ public class SlaMetricsServiceTests
             .ReturnsAsync(sessions);
 
         var metricsRepo = new Mock<IMetricsRepository>();
-        metricsRepo.Setup(r => r.GetAppInstallSummariesByTenantAsync(tenantId))
+        metricsRepo.Setup(r => r.GetAppInstallSummariesByTenantAsync(tenantId, It.IsAny<DateTime?>()))
             .ReturnsAsync(appInstalls ?? new List<AppInstallSummary>());
 
         var configService = new Mock<TenantConfigurationService>(

src/Backend/AutopilotMonitor.Functions.Tests/SlaTenantStatusLifecycleTests.cs

@@ -196,13 +196,13 @@ public class SlaTenantStatusLifecycleTests
             _sessionRepo.Setup(r => r.GetSessionsPageAsync(It.IsAny<string>(), It.IsAny<int?>(), It.IsAny<int>(), It.IsAny<string?>()))
                 .ReturnsAsync(new RawPage<SessionSummary>(new List<SessionSummary>(), null));
             // Default: no app installs
-            _metricsRepo.Setup(r => r.GetAppInstallSummariesByTenantAsync(It.IsAny<string>()))
+            _metricsRepo.Setup(r => r.GetAppInstallSummariesByTenantAsync(It.IsAny<string>(), It.IsAny<DateTime?>()))
                 .ReturnsAsync(new List<AppInstallSummary>());
         }
 
         public void SetAppInstalls(string tenantId, List<AppInstallSummary> apps)
         {
-            _metricsRepo.Setup(r => r.GetAppInstallSummariesByTenantAsync(tenantId)).ReturnsAsync(apps);
+            _metricsRepo.Setup(r => r.GetAppInstallSummariesByTenantAsync(tenantId, It.IsAny<DateTime?>())).ReturnsAsync(apps);
         }
 
         public void SetTenants(params TenantConfiguration[] tenants)
@@ -427,7 +427,7 @@ public class SlaTenantStatusLifecycleTests
         var opsSvc = new OpsEventService(opsRepo.Object, NullLogger<OpsEventService>.Instance, alertDispatch);
 
         var metricsRepo = new Mock<IMetricsRepository>();
-        metricsRepo.Setup(r => r.GetAppInstallSummariesByTenantAsync(It.IsAny<string>()))
+        metricsRepo.Setup(r => r.GetAppInstallSummariesByTenantAsync(It.IsAny<string>(), It.IsAny<DateTime?>()))
             .ReturnsAsync(new List<AppInstallSummary>());
         var svc = new SlaBreachEvaluationService(
             tenantConfigSvc, configRepoMock.Object, maintenanceRepo.Object, sessionRepo.Object,
@@ -862,7 +862,7 @@ public class SlaTenantStatusLifecycleTests
 
             _sessionRepo.Setup(r => r.GetSessionsPageAsync(It.IsAny<string>(), It.IsAny<int?>(), It.IsAny<int>(), It.IsAny<string?>()))
                 .ReturnsAsync(new RawPage<SessionSummary>(new List<SessionSummary>(), null));
-            _metricsRepo.Setup(r => r.GetAppInstallSummariesByTenantAsync(It.IsAny<string>()))
+            _metricsRepo.Setup(r => r.GetAppInstallSummariesByTenantAsync(It.IsAny<string>(), It.IsAny<DateTime?>()))
                 .ReturnsAsync(new List<AppInstallSummary>());
         }
 
@@ -873,7 +873,7 @@ public class SlaTenantStatusLifecycleTests
             => _maintenanceRepo.Setup(r => r.GetSessionsByDateRangeAsync(It.IsAny<DateTime>(), It.IsAny<DateTime>(), tenantId)).ReturnsAsync(sessions);
 
         public void SetAppInstalls(string tenantId, List<AppInstallSummary> apps)
-            => _metricsRepo.Setup(r => r.GetAppInstallSummariesByTenantAsync(tenantId)).ReturnsAsync(apps);
+            => _metricsRepo.Setup(r => r.GetAppInstallSummariesByTenantAsync(tenantId, It.IsAny<DateTime?>())).ReturnsAsync(apps);
     }
 
     /// <summary>

src/Backend/AutopilotMonitor.Functions.Tests/UsageMetricsServiceWindowTests.cs

@@ -24,9 +24,9 @@ public class UsageMetricsServiceWindowTests
             .ReturnsAsync(new UserActivityMetrics());
         metricsRepo.Setup(r => r.GetAllUserActivityMetricsAsync())
             .ReturnsAsync(new UserActivityMetrics());
-        metricsRepo.Setup(r => r.GetAllAppInstallSummariesAsync())
+        metricsRepo.Setup(r => r.GetAllAppInstallSummariesAsync(It.IsAny<DateTime?>()))
             .ReturnsAsync(new List<AppInstallSummary>());
-        metricsRepo.Setup(r => r.GetAppInstallSummariesByTenantAsync(It.IsAny<string>()))
+        metricsRepo.Setup(r => r.GetAppInstallSummariesByTenantAsync(It.IsAny<string>(), It.IsAny<DateTime?>()))
             .ReturnsAsync(new List<AppInstallSummary>());
         metricsRepo.Setup(r => r.GetPlatformStatsAsync())
             .ReturnsAsync((PlatformStats?)null);

src/Backend/AutopilotMonitor.Functions/DataAccess/TableStorage/TableMetricsRepository.cs

@@ -35,11 +35,11 @@ namespace AutopilotMonitor.Functions.DataAccess.TableStorage
         public Task<bool> StoreAppInstallSummaryAsync(AppInstallSummary summary)
             => _storage.StoreAppInstallSummaryAsync(summary);
 
-        public Task<List<AppInstallSummary>> GetAppInstallSummariesByTenantAsync(string tenantId)
-            => _storage.GetAppInstallSummariesByTenantAsync(tenantId);
+        public Task<List<AppInstallSummary>> GetAppInstallSummariesByTenantAsync(string tenantId, DateTime? sinceUtc = null)
+            => _storage.GetAppInstallSummariesByTenantAsync(tenantId, sinceUtc);
 
-        public Task<List<AppInstallSummary>> GetAllAppInstallSummariesAsync()
-            => _storage.GetAllAppInstallSummariesAsync();
+        public Task<List<AppInstallSummary>> GetAllAppInstallSummariesAsync(DateTime? sinceUtc = null)
+            => _storage.GetAllAppInstallSummariesAsync(sinceUtc);
 
         public Task<PlatformStats?> GetPlatformStatsAsync()
             => _storage.GetPlatformStatsAsync();

src/Backend/AutopilotMonitor.Functions/Functions/Apps/AppsAnalyticsHelper.cs

@@ -1,4 +1,5 @@
 using System.Collections.Specialized;
+using System.Threading;
 using AutopilotMonitor.Shared.DataAccess;
 using AutopilotMonitor.Shared.Models;
 
@@ -66,17 +67,55 @@ namespace AutopilotMonitor.Functions.Functions.Apps
 
         // ── Data loaders ────────────────────────────────────────────────────
 
+        /// <summary>Caps concurrent session point-reads in the device-model join so a wide app doesn't fan out hundreds of simultaneous Table reads.</summary>
+        private const int SessionJoinConcurrency = 10;
+
         /// <summary>
-        /// Loads app install summaries for the given scope.
+        /// Loads app install summaries for the given scope, scoped server-side to the last
+        /// <paramref name="days"/> days via a <c>StartedAt ge</c> filter (so a days=30 view does not
+        /// dematerialize the full StartedAt history). The cutoff is derived just before the in-memory
+        /// cutoff the Build* methods re-apply, so the server filter is never narrower than the in-memory
+        /// one — at worst it returns a few extra boundary rows that the in-memory filter trims.
         /// - tenantId != null → tenant-scoped (per-tenant endpoint or global admin viewing one tenant)
         /// - tenantId == null → all tenants (global admin aggregated view)
         /// </summary>
         public static async Task<List<AppInstallSummary>> LoadSummariesAsync(
-            IMetricsRepository repo, string? tenantId)
+            IMetricsRepository repo, string? tenantId, int days)
         {
+            var sinceUtc = DateTime.UtcNow.AddDays(-days);
             return string.IsNullOrEmpty(tenantId)
-                ? await repo.GetAllAppInstallSummariesAsync()
-                : await repo.GetAppInstallSummariesByTenantAsync(tenantId);
+                ? await repo.GetAllAppInstallSummariesAsync(sinceUtc)
+                : await repo.GetAppInstallSummariesByTenantAsync(tenantId, sinceUtc);
+        }
+
+        /// <summary>
+        /// Resolves the (TenantId, SessionId) → SessionSummary lookup used by the device-model join.
+        /// Point-reads run with bounded concurrency (<see cref="SessionJoinConcurrency"/>) rather than the
+        /// previous serial await-in-loop, which cost one sequential round-trip per distinct session.
+        /// Keys with an empty tenant or session id are skipped; misses (deleted session) are simply absent.
+        /// </summary>
+        private static async Task<Dictionary<string, SessionSummary>> LoadSessionLookupAsync(
+            ISessionRepository sessionRepo, IEnumerable<(string TenantId, string SessionId)> keys)
+        {
+            var distinct = keys
+                .Where(k => !string.IsNullOrEmpty(k.TenantId) && !string.IsNullOrEmpty(k.SessionId))
+                .Distinct()
+                .ToList();
+
+            using var gate = new SemaphoreSlim(SessionJoinConcurrency);
+            var tasks = distinct.Select(async key =>
+            {
+                await gate.WaitAsync();
+                try { return (key, sess: await sessionRepo.GetSessionAsync(key.TenantId, key.SessionId)); }
+                finally { gate.Release(); }
+            });
+
+            var results = await Task.WhenAll(tasks);
+
+            var lookup = new Dictionary<string, SessionSummary>();
+            foreach (var (key, sess) in results)
+                if (sess != null) lookup[$"{key.TenantId}|{key.SessionId}"] = sess;
+            return lookup;
         }
 
         // ── /apps/list ──────────────────────────────────────────────────────
@@ -308,14 +347,8 @@ namespace AutopilotMonitor.Functions.Functions.Apps
             // Device-model correlation: join via session lookup.
             // Global-admin (no tenant filter) summaries may span multiple tenants, so we use
             // each summary's own TenantId for the lookup instead of a single passed-in tenantId.
-            var distinctKeys = summaries.Select(s => (s.TenantId, s.SessionId)).Distinct().ToList();
-            var sessionLookup = new Dictionary<string, SessionSummary>();
-            foreach (var (tid, sid) in distinctKeys)
-            {
-                if (string.IsNullOrEmpty(tid) || string.IsNullOrEmpty(sid)) continue;
-                var sess = await sessionRepo.GetSessionAsync(tid, sid);
-                if (sess != null) sessionLookup[$"{tid}|{sid}"] = sess;
-            }
+            var sessionLookup = await LoadSessionLookupAsync(
+                sessionRepo, summaries.Select(s => (s.TenantId, s.SessionId)));
 
             var deviceModelBreakdown = summaries
                 .Where(s => sessionLookup.ContainsKey($"{s.TenantId}|{s.SessionId}"))
@@ -411,14 +444,8 @@ namespace AutopilotMonitor.Functions.Functions.Apps
 
             // Batch-fetch sessions for device info. Uses each summary's TenantId so global-admin
             // aggregated view works correctly across tenants.
-            var distinctKeys = summaries.Select(s => (s.TenantId, s.SessionId)).Distinct().ToList();
-            var sessionLookup = new Dictionary<string, SessionSummary>();
-            foreach (var (tid, sid) in distinctKeys)
-            {
-                if (string.IsNullOrEmpty(tid) || string.IsNullOrEmpty(sid)) continue;
-                var sess = await sessionRepo.GetSessionAsync(tid, sid);
-                if (sess != null) sessionLookup[$"{tid}|{sid}"] = sess;
-            }
+            var sessionLookup = await LoadSessionLookupAsync(
+                sessionRepo, summaries.Select(s => (s.TenantId, s.SessionId)));
 
             if (!string.IsNullOrWhiteSpace(modelFilter))
             {

src/Backend/AutopilotMonitor.Functions/Functions/Apps/GetAppAnalyticsFunction.cs

@@ -50,7 +50,7 @@ namespace AutopilotMonitor.Functions.Functions.Apps
                 if (int.TryParse(query["days"], out var parsedDays) && parsedDays > 0 && parsedDays <= 365)
                     days = parsedDays;
 
-                var summaries = await AppsAnalyticsHelper.LoadSummariesAsync(_metricsRepo, tenantId);
+                var summaries = await AppsAnalyticsHelper.LoadSummariesAsync(_metricsRepo, tenantId, days);
                 var body = await AppsAnalyticsHelper.BuildAnalyticsResponseAsync(
                     summaries, _sessionRepo, decodedAppName, days);
 

src/Backend/AutopilotMonitor.Functions/Functions/Apps/GetAppSessionsFunction.cs

@@ -64,7 +64,7 @@ namespace AutopilotMonitor.Functions.Functions.Apps
                 if (int.TryParse(query["limit"], out var parsedLimit) && parsedLimit > 0)
                     limit = Math.Min(parsedLimit, MaxLimit);
 
-                var summaries = await AppsAnalyticsHelper.LoadSummariesAsync(_metricsRepo, tenantId);
+                var summaries = await AppsAnalyticsHelper.LoadSummariesAsync(_metricsRepo, tenantId, days);
                 var body = await AppsAnalyticsHelper.BuildSessionsResponseAsync(
                     summaries, _sessionRepo, decodedAppName, days,
                     statusFilter, modelFilter, versionFilter, offset, limit);

src/Backend/AutopilotMonitor.Functions/Functions/Apps/GetAppsListFunction.cs

@@ -46,7 +46,7 @@ namespace AutopilotMonitor.Functions.Functions.Apps
                     return bad;
                 }
 
-                var summaries = await AppsAnalyticsHelper.LoadSummariesAsync(_metricsRepo, tenantId);
+                var summaries = await AppsAnalyticsHelper.LoadSummariesAsync(_metricsRepo, tenantId, days);
                 var body = AppsAnalyticsHelper.BuildAppsListResponse(
                     summaries, days, paging.PageSize, paging.Skip,
                     nextOffset => $"/api/apps/list?days={days}&pageSize={paging.PageSize}&skip={nextOffset}");

src/Backend/AutopilotMonitor.Functions/Functions/Apps/GetGlobalAppAnalyticsFunction.cs

@@ -60,7 +60,7 @@ namespace AutopilotMonitor.Functions.Functions.Apps
                     "Global apps/{App}/analytics requested (user: {User}, tenantId: {TenantId}, days: {Days})",
                     decodedAppName, userEmail, scopedTenantId ?? "<all>", days);
 
-                var summaries = await AppsAnalyticsHelper.LoadSummariesAsync(_metricsRepo, scopedTenantId);
+                var summaries = await AppsAnalyticsHelper.LoadSummariesAsync(_metricsRepo, scopedTenantId, days);
                 var body = await AppsAnalyticsHelper.BuildAnalyticsResponseAsync(
                     summaries, _sessionRepo, decodedAppName, days);
 

src/Backend/AutopilotMonitor.Functions/Functions/Apps/GetGlobalAppSessionsFunction.cs

@@ -75,7 +75,7 @@ namespace AutopilotMonitor.Functions.Functions.Apps
                     "Global apps/{App}/sessions requested (user: {User}, tenantId: {TenantId})",
                     decodedAppName, userEmail, scopedTenantId ?? "<all>");
 
-                var summaries = await AppsAnalyticsHelper.LoadSummariesAsync(_metricsRepo, scopedTenantId);
+                var summaries = await AppsAnalyticsHelper.LoadSummariesAsync(_metricsRepo, scopedTenantId, days);
                 var body = await AppsAnalyticsHelper.BuildSessionsResponseAsync(
                     summaries, _sessionRepo, decodedAppName, days,
                     statusFilter, modelFilter, versionFilter, offset, limit);

src/Backend/AutopilotMonitor.Functions/Functions/Apps/GetGlobalAppsListFunction.cs

@@ -57,7 +57,7 @@ namespace AutopilotMonitor.Functions.Functions.Apps
                     return bad;
                 }
 
-                var summaries = await AppsAnalyticsHelper.LoadSummariesAsync(_metricsRepo, scopedTenantId);
+                var summaries = await AppsAnalyticsHelper.LoadSummariesAsync(_metricsRepo, scopedTenantId, days);
                 var tenantQs = string.IsNullOrEmpty(scopedTenantId) ? string.Empty : $"&tenantId={scopedTenantId}";
                 var body = AppsAnalyticsHelper.BuildAppsListResponse(
                     summaries, days, paging.PageSize, paging.Skip,

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

@@ -40,7 +40,9 @@ namespace AutopilotMonitor.Functions.Functions.Metrics
 
                 var cutoff = DateTime.UtcNow.AddDays(-days);
 
-                var allSummaries = await _metricsRepo.GetAppInstallSummariesByTenantAsync(tenantId);
+                // Push the window server-side so only in-window rows are deserialized. The in-memory
+                // Where below stays as the exact trim (the OData StartedAt filter is second-granular).
+                var allSummaries = await _metricsRepo.GetAppInstallSummariesByTenantAsync(tenantId, cutoff);
                 var summaries = allSummaries.Where(s => s.StartedAt >= cutoff).ToList();
 
                 // Aggregation (slowest/failing ranking + Delivery Optimization rollup) is shared

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

@@ -50,7 +50,9 @@ namespace AutopilotMonitor.Functions.Functions.Metrics
 
                 var cutoff = DateTime.UtcNow.AddDays(-days);
                 var sessions = await _maintenanceRepo.GetSessionsByDateRangeAsync(cutoff, DateTime.UtcNow.AddDays(1), tenantId);
-                var allSummaries = await _metricsRepo.GetAppInstallSummariesByTenantAsync(tenantId);
+                // Push the window server-side so only in-window rows are deserialized. The in-memory
+                // Where below stays as the exact trim (the OData StartedAt filter is second-granular).
+                var allSummaries = await _metricsRepo.GetAppInstallSummariesByTenantAsync(tenantId, cutoff);
                 var summaries = allSummaries.Where(s => s.StartedAt >= cutoff).ToList();
 
                 var result = ComputeGeographicMetrics(sessions, summaries, groupBy);

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

@@ -41,9 +41,11 @@ namespace AutopilotMonitor.Functions.Functions.Metrics
 
                 var cutoff = DateTime.UtcNow.AddDays(-days);
 
+                // Push the window server-side so only in-window rows are deserialized. The in-memory
+                // Where below stays as the exact trim (the OData StartedAt filter is second-granular).
                 var allSummaries = !string.IsNullOrWhiteSpace(tenantIdFilter)
-                    ? await _metricsRepo.GetAppInstallSummariesByTenantAsync(tenantIdFilter)
-                    : await _metricsRepo.GetAllAppInstallSummariesAsync();
+                    ? await _metricsRepo.GetAppInstallSummariesByTenantAsync(tenantIdFilter, cutoff)
+                    : await _metricsRepo.GetAllAppInstallSummariesAsync(cutoff);
                 var summaries = allSummaries.Where(s => s.StartedAt >= cutoff).ToList();
 
                 // Aggregation (slowest/failing ranking + Delivery Optimization rollup) is shared

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

@@ -47,9 +47,11 @@ namespace AutopilotMonitor.Functions.Functions.Metrics
                 var sessions = !string.IsNullOrWhiteSpace(tenantIdFilter)
                     ? await _maintenanceRepo.GetSessionsByDateRangeAsync(cutoff, DateTime.UtcNow.AddDays(1), tenantIdFilter)
                     : await _maintenanceRepo.GetSessionsByDateRangeAsync(cutoff, DateTime.UtcNow.AddDays(1));
+                // Push the window server-side so only in-window rows are deserialized. The in-memory
+                // Where below stays as the exact trim (the OData StartedAt filter is second-granular).
                 var allSummaries = !string.IsNullOrWhiteSpace(tenantIdFilter)
-                    ? await _metricsRepo.GetAppInstallSummariesByTenantAsync(tenantIdFilter)
-                    : await _metricsRepo.GetAllAppInstallSummariesAsync();
+                    ? await _metricsRepo.GetAppInstallSummariesByTenantAsync(tenantIdFilter, cutoff)
+                    : await _metricsRepo.GetAllAppInstallSummariesAsync(cutoff);
                 var summaries = allSummaries.Where(s => s.StartedAt >= cutoff).ToList();
 
                 var result = GetGeographicMetricsFunction.ComputeGeographicMetrics(sessions, summaries, groupBy);

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

@@ -328,16 +328,24 @@ namespace AutopilotMonitor.Functions.Services
         }
 
         /// <summary>
-        /// Gets all app install summaries for a tenant (fleet-level metrics)
+        /// Gets app install summaries for a tenant (fleet-level metrics). When <paramref name="sinceUtc"/>
+        /// is supplied, a server-side <c>StartedAt ge</c> filter is applied so a windowed view (e.g. the
+        /// app dashboard's days=30) does not dematerialize the tenant's entire StartedAt history. The
+        /// filter still scans the partition (no secondary index on StartedAt), but only the in-window rows
+        /// are deserialized and returned over the wire. <paramref name="sinceUtc"/> is a server-derived
+        /// DateTime (never caller-supplied text), so interpolating it into the OData filter is injection-safe.
         /// </summary>
-        public async Task<List<AppInstallSummary>> GetAppInstallSummariesByTenantAsync(string tenantId)
+        public async Task<List<AppInstallSummary>> GetAppInstallSummariesByTenantAsync(string tenantId, DateTime? sinceUtc = null)
         {
             SecurityValidator.EnsureValidGuid(tenantId, nameof(tenantId));
 
             try
             {
                 var tableClient = _tableServiceClient.GetTableClient(Constants.TableNames.AppInstallSummaries);
-                var query = tableClient.QueryAsync<TableEntity>(filter: $"PartitionKey eq '{tenantId}'");
+                var filter = $"PartitionKey eq '{tenantId}'";
+                if (sinceUtc.HasValue)
+                    filter += $" and StartedAt ge datetime'{sinceUtc.Value:yyyy-MM-ddTHH:mm:ss}Z'";
+                var query = tableClient.QueryAsync<TableEntity>(filter: filter);
 
                 var summaries = new List<AppInstallSummary>();
                 await foreach (var entity in query)
@@ -355,14 +363,20 @@ namespace AutopilotMonitor.Functions.Services
         }
 
         /// <summary>
-        /// Gets all app install summaries across all tenants (for global admin mode)
+        /// Gets all app install summaries across all tenants (for global admin mode). When
+        /// <paramref name="sinceUtc"/> is supplied, a server-side <c>StartedAt ge</c> filter scopes the
+        /// (otherwise full-table) scan to the window so only in-window rows are deserialized.
+        /// <paramref name="sinceUtc"/> is server-derived, so interpolating it is injection-safe.
         /// </summary>
-        public async Task<List<AppInstallSummary>> GetAllAppInstallSummariesAsync()
+        public async Task<List<AppInstallSummary>> GetAllAppInstallSummariesAsync(DateTime? sinceUtc = null)
         {
             try
             {
                 var tableClient = _tableServiceClient.GetTableClient(Constants.TableNames.AppInstallSummaries);
-                var query = tableClient.QueryAsync<TableEntity>();
+                var filter = sinceUtc.HasValue
+                    ? $"StartedAt ge datetime'{sinceUtc.Value:yyyy-MM-ddTHH:mm:ss}Z'"
+                    : null;
+                var query = tableClient.QueryAsync<TableEntity>(filter: filter);
 
                 var summaries = new List<AppInstallSummary>();
                 await foreach (var entity in query)

src/Shared/AutopilotMonitor.Shared/DataAccess/IMetricsRepository.cs

@@ -21,8 +21,10 @@ namespace AutopilotMonitor.Shared.DataAccess
 
         // --- App Install Summaries ---
         Task<bool> StoreAppInstallSummaryAsync(AppInstallSummary summary);
-        Task<List<AppInstallSummary>> GetAppInstallSummariesByTenantAsync(string tenantId);
-        Task<List<AppInstallSummary>> GetAllAppInstallSummariesAsync();
+        /// <summary>Gets a tenant's app install summaries. Pass <paramref name="sinceUtc"/> to push the window's <c>StartedAt ge</c> filter server-side; null returns the full partition (legacy behaviour).</summary>
+        Task<List<AppInstallSummary>> GetAppInstallSummariesByTenantAsync(string tenantId, DateTime? sinceUtc = null);
+        /// <summary>Gets all tenants' app install summaries. Pass <paramref name="sinceUtc"/> to scope the (otherwise full-table) scan to the window; null returns everything (legacy behaviour).</summary>
+        Task<List<AppInstallSummary>> GetAllAppInstallSummariesAsync(DateTime? sinceUtc = null);
 
         // --- Platform Stats ---
         Task<PlatformStats?> GetPlatformStatsAsync();