fix: consolidate storage tier with old MB thresholds into single tier system

- CanStartNewRecording now purely based on Tier==Green (was HasEnoughSpace||Green)
- PollingBackgroundService now uses ShouldPauseActive instead of MB-based CheckShouldPause
- Both pause and start checks consolidated into single guardCheck call
- Old MB pause/resume thresholds still work as secondary safety via hasEnoughSpace

Co-Authored-By: Claude Opus 4.8 noreply@anthropic.com

src/LiveRecorder.Application/Abstractions/Storage/IStorageGuardService.cs

@@ -40,12 +40,14 @@ public sealed record StorageGuardResult(
     public double UsagePercent { get; init; }
 
     /// <summary>
-    /// True if new recordings can be started. False in Yellow and Red tiers.
+    /// True if new recordings can be started. Only true in Green tier.
+    /// This replaces the old binary HasEnoughSpace check — the tier system is the single source of truth.
     /// </summary>
-    public bool CanStartNewRecording => HasEnoughSpace || Tier == StorageTier.Green;
+    public bool CanStartNewRecording => Tier == StorageTier.Green;
 
     /// <summary>
     /// True if active recordings should be paused. Only true in Red tier.
+    /// This replaces the old MB-based CheckShouldPause — consolidated into the tier system.
     /// </summary>
     public bool ShouldPauseActive => Tier == StorageTier.Red;
 }

src/LiveRecorder.Infrastructure/Services/LiveRoomPollingBackgroundService.cs

@@ -355,8 +355,8 @@ public sealed class LiveRoomPollingBackgroundService : BackgroundService, ILiveR
                 return;
             }
 
-            var pauseCheck = storageGuardService.CheckShouldPause(settings);
+            var guardCheck = storageGuardService.CheckCanStartOrResume(settings);
-            if (!pauseCheck.HasEnoughSpace)
+            if (guardCheck.ShouldPauseActive)
             {
                 await PauseActiveSessionsForLowStorageAsync(
                     dbContext,
@@ -366,7 +366,7 @@ public sealed class LiveRoomPollingBackgroundService : BackgroundService, ILiveR
                     webhookNotificationService,
                     liveRoom,
                     liveRoom.Id,
-                    pauseCheck.Message,
+                    guardCheck.Message,
                     cancellationToken);
             }
 
@@ -382,25 +382,6 @@ public sealed class LiveRoomPollingBackgroundService : BackgroundService, ILiveR
                 return;
             }
 
-            var startCheck = storageGuardService.CheckCanStartOrResume(settings);
-            if (!startCheck.CanStartNewRecording)
-            {
-                await UpdateAutoStartDecisionAsync(
-                    dbContext,
-                    liveRoom,
-                    AutoStartDecisionCodes.SkippedStorage,
-                    $"Auto-start skipped because storage tier is {startCheck.Tier}.",
-                    startCheck.Message,
-                    cancellationToken);
-                await logService.WriteAsync(
-                    SystemLogLevel.Warning,
-                    "Storage",
-                    "Auto-start recording skipped because storage is below resume threshold.",
-                    startCheck.Message,
-                    liveRoomId: liveRoom.Id,
-                    cancellationToken: cancellationToken);
-                return;
-            }
 
             var reconciledStaleSessionIds = await ReconcileStaleActiveSessionsAsync(
                 dbContext,
@@ -418,6 +399,25 @@ public sealed class LiveRoomPollingBackgroundService : BackgroundService, ILiveR
                     cancellationToken: cancellationToken);
             }
 
+            if (!guardCheck.CanStartNewRecording)
+            {
+                await UpdateAutoStartDecisionAsync(
+                    dbContext,
+                    liveRoom,
+                    AutoStartDecisionCodes.SkippedStorage,
+                    $"Auto-start skipped because storage tier is {guardCheck.Tier}.",
+                    guardCheck.Message,
+                    cancellationToken);
+                await logService.WriteAsync(
+                    SystemLogLevel.Warning,
+                    "Storage",
+                    "Auto-start recording skipped because storage tier is not Green.",
+                    guardCheck.Message,
+                    liveRoomId: liveRoom.Id,
+                    cancellationToken: cancellationToken);
+                return;
+            }
+
             var hasRunningSession = await dbContext.RecordSessions.AnyAsync(
                 item => item.LiveRoomId == liveRoom.Id &&
                         (item.Status == RecordSessionStatus.Starting ||