Merge pull request 'Stop an attach's own replay landing in the middle of a test's frames' (#18) from claude/fix-failed-test-3e1719 into main

Reviewed-on: #18

tests/DodoSSH.Client.Terminal.Tests/TerminalWorkspaceTests.cs

@@ -27,6 +27,12 @@ public sealed class TerminalWorkspaceTests
     /// <summary>How long <see cref="WaitUntilAsync"/> polls before calling it a failure.</summary>
     private static readonly TimeSpan PollTimeout = TimeSpan.FromSeconds(10);
 
+    /// <summary>
+    /// How long <see cref="ConnectRendererAsync"/> waits for the attach's replay before calling it a
+    /// failure. Generous, because it bounds a hang rather than timing anything.
+    /// </summary>
+    private static readonly TimeSpan ReplayTimeout = TimeSpan.FromSeconds(10);
+
     [Fact]
     public async Task WaitingForARendererThatNeverAttaches_GivesUp()
     {
@@ -773,11 +779,20 @@ public sealed class TerminalWorkspaceTests
     /// </para>
     /// <para>
     /// <c>WaitForRendererAsync</c> answers only for the first renderer ever to attach, so a second call
-    /// returns immediately without proving anything about the second socket. That is enough here and is
-    /// not luck: the only frames a second socket is given are the replay, and the replay is *caused* by the
-    /// attach — <see cref="TerminalWorkspace.RendererReattached"/> and the frames before it cannot be sent
-    /// early. The day a test sends something else down a reattached socket, this needs the data plane's own
-    /// <c>SocketAttached</c>, which the workspace does not forward today.
+    /// returns immediately without proving anything about the second socket — and even for the first it
+    /// answers too early for what the callers here need. It completes when the socket is attached, which
+    /// is before <see cref="TerminalWorkspace.ReplayAfterAttachAsync"/> has run: that is fired and
+    /// forgotten from the accept thread, and a thread-pool that deschedules it for a timeslice lets the
+    /// test open a session in the meantime. The replay then finds that session live and sends it a second,
+    /// replay-flagged <c>SessionOpened</c> — harmless to the page, which treats it as idempotent, but it
+    /// lands in the middle of the frames the test is counting on.
+    /// </para>
+    /// <para>
+    /// ◆ SO WAIT FOR THE REPLAY TO BE OVER, NOT ONLY FOR THE ATTACH. <c>RendererReattached</c> is raised
+    /// as the last thing the replay does, so a socket this returns has had every frame the attach itself
+    /// causes, and nothing but what the test does next can put another on it. Subscribed before the
+    /// upgrade, because the replay for a socket that attaches quickly can be over before this method gets
+    /// to look.
     /// </para>
     /// </remarks>
     private static async Task<ClientWebSocket> ConnectRendererAsync(TerminalWorkspace workspace)
@@ -795,17 +810,29 @@ public sealed class TerminalWorkspaceTests
             "Origin",
             string.Create(CultureInfo.InvariantCulture, $"http://127.0.0.1:{workspace.PageUrl.Port}"));
 
+        var replayed = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
+
+        void OnReattached(object? sender, EventArgs e) => replayed.TrySetResult();
+
+        workspace.RendererReattached += OnReattached;
+
         try
         {
             await client.ConnectAsync(new Uri(socketUrl), TestContext.Current.CancellationToken);
 
             await workspace.WaitForRendererAsync(TestContext.Current.CancellationToken);
+
+            await replayed.Task.WaitAsync(ReplayTimeout, TestContext.Current.CancellationToken);
         }
         catch
         {
             client.Dispose();
             throw;
         }
+        finally
+        {
+            workspace.RendererReattached -= OnReattached;
+        }
 
         return client;
     }