Prevent reboot bridge request completing too soon

src/Tgstation.Server.Host/Components/Session/ISessionController.cs

@@ -69,6 +69,11 @@ namespace Tgstation.Server.Host.Components.Session
 		/// </summary>
 		Task OnReboot { get; }
 
+		/// <summary>
+		/// A <see cref="Task"/> that must complete before a TgsReboot() bridge request can complete.
+		/// </summary>
+		Task RebootGate { set; }
+
 		/// <summary>
 		/// A <see cref="Task"/> that completes when the server calls /world/TgsInitializationComplete().
 		/// </summary>

src/Tgstation.Server.Host/Components/Session/SessionController.cs

@@ -75,6 +75,26 @@ namespace Tgstation.Server.Host.Components.Session
 		/// <inheritdoc />
 		public Task OnReboot => rebootTcs.Task;
 
+		/// <inheritdoc />
+		public Task RebootGate
+		{
+			get => rebootGate;
+			set
+			{
+				var tcs = new TaskCompletionSource();
+				Task toAwait = null;
+				async Task Wrap()
+				{
+					await tcs.Task;
+					await toAwait;
+					await value;
+				}
+
+				toAwait = Interlocked.Exchange(ref rebootGate, Wrap());
+				tcs.SetResult();
+			}
+		}
+
 		/// <inheritdoc />
 		public Task OnPrime => primeTcs.Task;
 
@@ -164,6 +184,11 @@ namespace Tgstation.Server.Host.Components.Session
 		/// </summary>
 		volatile TaskCompletionSource primeTcs;
 
+		/// <summary>
+		/// Backing field for <see cref="RebootGate"/>.
+		/// </summary>
+		volatile Task rebootGate;
+
 		/// <summary>
 		/// The number of currently active calls to <see cref="ProcessBridgeRequest(BridgeParameters, CancellationToken)"/> from TgsReboot().
 		/// </summary>
@@ -254,6 +279,8 @@ namespace Tgstation.Server.Host.Components.Session
 			rebootTcs = new TaskCompletionSource();
 			primeTcs = new TaskCompletionSource();
 
+			rebootGate = Task.CompletedTask;
+
 			// Run this asynchronously because we want to try to avoid any effects sending topics to the server while the initial bridge request is processing
 			// It MAY be the source of a DD crash. See this gist https://gist.github.com/Cyberboss/7776bbeff3a957d76affe0eae95c9f14
 			// Worth further investigation as to if that sequence of events is a reliable crash vector and opening a BYOND bug if it is
@@ -751,6 +778,7 @@ namespace Tgstation.Server.Host.Components.Session
 						}
 
 						Interlocked.Exchange(ref rebootTcs, new TaskCompletionSource()).SetResult();
+						await RebootGate;
 					}
 					finally
 					{

src/Tgstation.Server.Host/Components/Watchdog/WatchdogBase.cs

@@ -804,6 +804,8 @@ namespace Tgstation.Server.Host.Components.Watchdog
 				var ranInitialDmbCheck = false;
 				for (ulong iteration = 1; nextAction != MonitorAction.Exit; ++iteration)
 					using (LogContext.PushProperty(SerilogContextHelper.WatchdogMonitorIterationContextProperty, iteration))
+					{
+						TaskCompletionSource nextMonitorWakeupTcs = new TaskCompletionSource();
 						try
 						{
 							Logger.LogTrace("Iteration {iteration} of monitor loop", iteration);
@@ -821,6 +823,7 @@ namespace Tgstation.Server.Host.Components.Watchdog
 									oldTask = newTaskFactory();
 								}
 
+								controller.RebootGate = nextMonitorWakeupTcs.Task;
 								if (lastController == controller)
 								{
 									TryUpdateTask(ref activeServerLifetime, () => controller.Lifetime);
@@ -967,6 +970,11 @@ namespace Tgstation.Server.Host.Components.Watchdog
 								nextAction = MonitorAction.Continue;
 							}
 						}
+						finally
+						{
+							nextMonitorWakeupTcs.SetResult();
+						}
+					}
 			}
 			catch (OperationCanceledException)
 			{