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.

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

@@ -149,6 +149,31 @@ public sealed class TerminalWorkspaceTests
         workspace.IsSessionLive(second).ShouldBeTrue("closing one tab must not disturb another");
     }
 
+    /// <remarks>
+    /// The shell's connect path reads these back once, right after <see cref="TerminalWorkspace.OpenSessionAsync"/>
+    /// returns, to fill in the status bar's cipher and host-key facts — see <c>VaultViewModel.ConnectAndAnnounceAsync</c>.
+    /// Asserted the same way <see cref="LivenessIsAnsweredPerSession"/> asserts liveness: per session, and
+    /// null rather than thrown for an id this workspace never issued.
+    /// </remarks>
+    [Fact]
+    public async Task SessionFactsAreReadPerSession()
+    {
+        var connections = new FakeConnectionFactory();
+
+        await using var workspace = CreateWorkspace(connections);
+
+        var sessionId = await workspace.OpenSessionAsync(
+            Request(), TerminalSize.Default, TestContext.Current.CancellationToken);
+
+        var facts = workspace.GetSessionFacts(sessionId).ShouldNotBeNull();
+        var connection = connections.Connections.ShouldHaveSingleItem();
+
+        facts.Cipher.ShouldBe(connection.Cipher);
+        facts.HostKeyAlgorithm.ShouldBe(connection.HostKey.Algorithm);
+
+        workspace.GetSessionFacts(9999).ShouldBeNull("this workspace never issued that id");
+    }
+
     /// <remarks>
     /// <para>
     /// Inserting a snippet has to be able to say whether it arrived, and the transport cannot: it drops