retry the quick connect startup probe, and exit non-zero when a start fails

Emby.Server.Implementations/MediaEncoding/TranscodeStoreConnectivityProbe.cs

@@ -10,9 +10,14 @@ using StackExchange.Redis;
 namespace Emby.Server.Implementations.MediaEncoding;
 
 /// <summary>
-/// Pings the configured Redis transcode session store once at startup so an unreachable store is
-/// reported there instead of being discovered as a silent loss of cross-pod takeover.
+/// Reports the round trip to the configured Redis transcode session store once at startup, so the
+/// state of cross-pod takeover is visible where the server is started.
 /// </summary>
+/// <remarks>
+/// This reports, it does not gate. <see cref="ApplicationHost.InitializeServices"/> has already read the
+/// same connection for quick connect by the time this runs and has stopped startup if it could not be
+/// reached, so the error branch here only covers a store that went away in between.
+/// </remarks>
 public sealed class TranscodeStoreConnectivityProbe : IHostedService
 {
     private readonly IServiceProvider _serviceProvider;
@@ -34,7 +39,7 @@ public sealed class TranscodeStoreConnectivityProbe : IHostedService
     {
         try
         {
-            // Resolved here rather than injected: connecting must not be able to abort startup.
+            // Resolved here rather than injected so a store lost after the quick connect gate is reported.
             var redis = _serviceProvider.GetRequiredService<IConnectionMultiplexer>();
             var roundTrip = await redis.GetDatabase().PingAsync().ConfigureAwait(false);