Desktop: stop the status bar's session timer when the shell ends

src/DodoSSH.Client.Shell/ViewModels/TerminalTabViewModel.cs

@@ -274,6 +274,15 @@ internal sealed partial class TerminalTabViewModel : ObservableObject
     /// </remarks>
     internal DateTimeOffset? StartedAt { get; set; }
 
+    /// <summary>When the session behind this tab ended, or null while it has not.</summary>
+    /// <remarks>
+    /// What stops the status bar's timer. It used to go on counting from <see cref="StartedAt"/> to now over a
+    /// shell that had exited an hour earlier, which made "how long that shell ran" — the fact the remark above
+    /// keeps <see cref="StartedAt"/> for — the one thing it no longer said. Stamped by <see cref="Ended"/> from
+    /// the shell's clock, and cleared whenever a new session takes the tab.
+    /// </remarks>
+    internal DateTimeOffset? EndedAt { get; private set; }
+
     /// <summary>
     /// The negotiated server-to-client cipher, for the status bar — or null while there is no session.
     /// </summary>
@@ -620,6 +629,7 @@ internal sealed partial class TerminalTabViewModel : ObservableObject
         // stale-fact failure this pair exists to remove.
         EndReason = null;
         EndDescription = null;
+        EndedAt = null;
 
         IsLive = true;
         State = TerminalTabState.Open;
@@ -679,13 +689,14 @@ internal sealed partial class TerminalTabViewModel : ObservableObject
     /// live attempt dead. <see cref="Advance"/> guards its own reports for the same reason.
     /// </para>
     /// </remarks>
-    internal void Ended(SshSessionEnd end, string description)
+    internal void Ended(SshSessionEnd end, string description, DateTimeOffset at)
     {
         if (State is not TerminalTabState.Open)
         {
             return;
         }
 
+        EndedAt ??= at;
         EndReason = end;
         EndDescription = description;
         IsLive = false;
@@ -733,6 +744,7 @@ internal sealed partial class TerminalTabViewModel : ObservableObject
         // Cleared with the session they were facts about. Keeping them would put the previous connection's
         // cipher in the status bar beside a handshake that has not negotiated one yet.
         StartedAt = null;
+        EndedAt = null;
         Cipher = null;
         HostKeyAlgorithm = null;
         IdentityLabel = null;