refactor(runtime): own communication and social state

Construct chat history, negotiated channels, friends, squelch, and reply targets in one presentation-independent Runtime owner. Make live routing, retained UI, devtools, and current-runtime projections borrow the exact instances, preserve reconnect reset semantics, and publish failure-isolated reentrant-safe chat commits.

Co-authored-by: Codex <codex@openai.com>

src/AcDream.Core/Chat/ChatCommandTargetState.cs

@@ -0,0 +1,84 @@
+namespace AcDream.Core.Chat;
+
+/// <summary>
+/// Presentation-independent reply/retell targets derived from the committed
+/// chat transcript.
+/// </summary>
+/// <remarks>
+/// Incoming tells carry a non-zero sender GUID and update the reply target.
+/// Local outgoing tell echoes carry a zero sender GUID and place the target
+/// name in <see cref="ChatEntry.Sender"/>. This is the existing retail
+/// <c>@reply</c>/<c>@retell</c> behavior formerly owned by <c>ChatVM</c>.
+/// </remarks>
+public sealed class ChatCommandTargetState : IDisposable
+{
+    private readonly ChatLog _chat;
+    private readonly object _gate = new();
+    private string? _lastIncomingTellSender;
+    private string? _lastOutgoingTellTarget;
+    private bool _disposed;
+
+    public ChatCommandTargetState(ChatLog chat)
+    {
+        _chat = chat ?? throw new ArgumentNullException(nameof(chat));
+        _chat.EntryAppended += OnEntryAppended;
+    }
+
+    public string? LastIncomingTellSender
+    {
+        get
+        {
+            lock (_gate)
+                return _lastIncomingTellSender;
+        }
+    }
+
+    public string? LastOutgoingTellTarget
+    {
+        get
+        {
+            lock (_gate)
+                return _lastOutgoingTellTarget;
+        }
+    }
+
+    /// <summary>
+    /// Forget character-scoped command targets without clearing visible
+    /// transcript history.
+    /// </summary>
+    public void ResetSession()
+    {
+        lock (_gate)
+        {
+            _lastIncomingTellSender = null;
+            _lastOutgoingTellTarget = null;
+        }
+    }
+
+    public void Dispose()
+    {
+        lock (_gate)
+        {
+            if (_disposed)
+                return;
+            _disposed = true;
+            _chat.EntryAppended -= OnEntryAppended;
+        }
+    }
+
+    private void OnEntryAppended(ChatEntry entry)
+    {
+        if (entry.Kind != ChatKind.Tell || string.IsNullOrEmpty(entry.Sender))
+            return;
+
+        lock (_gate)
+        {
+            if (_disposed)
+                return;
+            if (entry.SenderGuid != 0u)
+                _lastIncomingTellSender = entry.Sender;
+            else
+                _lastOutgoingTellTarget = entry.Sender;
+        }
+    }
+}