Tests: wait for a dropped session's forwards to stop, not just for the tab to go dead

WhenTheSessionEnds_ItsForwardsSayTheyWentWithIt failed once under a full run. Ended clears IsLive
and then tells each forward its session is over, in one call. The app's dispatcher never splits that,
but the harness's post runs it on the fake shell's thread, so the test's poll on !IsLive could return
between the two and find the forwards still listening.

The test now also waits until every forward says "Stopped with the session.", the last thing
SessionEnded sets. A 300 ms sleep injected between the two steps fails the old test and passes the new
one; the full App.Tests suite passed three runs in a row.

tests/DodoSSH.Client.App.Tests/ShellFlowTests.Forwards.cs

@@ -114,6 +114,13 @@ public sealed partial class ShellFlowTests
 
         await EventuallyAsync(() => !tab.IsLive, "the dropped shell should have ended the session");
 
+        // Waited for in its own right rather than taken as read from IsLive. Ended clears IsLive and then
+        // ends the forwards in the same dispatcher turn, which the app's UI thread never splits — but this
+        // harness's post runs the ending on the fake shell's thread, so a poll from here can land between.
+        await EventuallyAsync(
+            () => tab.Forwards.All(row => row.Detail == "Stopped with the session."),
+            "the session's end should have reached its forwards");
+
         tab.Forwards.ShouldAllBe(row => row.State == PortForwardState.Stopped);
         tab.Forwards.ShouldAllBe(row => row.Detail == "Stopped with the session.");
         tab.Forwards.ShouldAllBe(row => !row.CanToggle);