Let a session's transport say what it negotiated

ISshConnection and ISftpSession both carry Cipher now — the server-to-client
algorithm off SSH.NET's own ConnectionInfo, captured once because a rekey is
not an event that library raises — and TerminalWorkspace.GetSessionFacts hands
that plus the host key's algorithm back per session, without ever handing over
the connection itself. Nothing reads either yet; the status bar that will is
the next commit.

src/DodoSSH.Client.Ssh/SshConnection.cs

@@ -98,6 +98,25 @@ public interface ISshConnection : IAsyncDisposable
     /// <summary>The host key that was accepted for this connection.</summary>
     HostKeyPresentation HostKey { get; }
 
+    /// <summary>
+    /// The negotiated server-to-client encryption algorithm, e.g. <c>aes256-gcm@openssh.com</c>.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// Read once, immediately after the handshake, off SSH.NET's own <c>ConnectionInfo.CurrentServerEncryption</c>.
+    /// The only event that could make this stale is a rekey, and SSH.NET raises no event for one and exposes no
+    /// way to ask again — there is nothing behind this property to go and re-read. A captured value is therefore
+    /// not a snapshot that might drift; it is the only value there has ever been a moment to observe.
+    /// </para>
+    /// <para>
+    /// <b>Server-to-client, not client-to-server.</b> SSH negotiates the two directions independently and a
+    /// server is free to choose differently for each, so the two can in principle disagree. This is the
+    /// direction the bytes drawn on a terminal pane travelled in, which is the fact a status bar showing what
+    /// the screen is made of should be naming.
+    /// </para>
+    /// </remarks>
+    string Cipher { get; }
+
     /// <summary>Opens an interactive shell with a pseudo-terminal.</summary>
     Task<ISshShellSession> OpenShellAsync(TerminalSize size, CancellationToken cancellationToken);
 }