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>

tests/AcDream.Core.Tests/Chat/ChatCommandTargetStateTests.cs

@@ -0,0 +1,48 @@
+using AcDream.Core.Chat;
+
+namespace AcDream.Core.Tests.Chat;
+
+public sealed class ChatCommandTargetStateTests
+{
+    [Fact]
+    public void TracksReplyAndRetellTargetsFromCommittedTranscript()
+    {
+        var chat = new ChatLog();
+        using var targets = new ChatCommandTargetState(chat);
+
+        chat.OnTellReceived("Bestie", "incoming", 0x50000001u);
+        chat.OnSelfSent(ChatKind.Tell, "outgoing", "Caith");
+
+        Assert.Equal("Bestie", targets.LastIncomingTellSender);
+        Assert.Equal("Caith", targets.LastOutgoingTellTarget);
+    }
+
+    [Fact]
+    public void ResetSessionForgetsTargetsButPreservesTranscript()
+    {
+        var chat = new ChatLog();
+        using var targets = new ChatCommandTargetState(chat);
+        chat.OnTellReceived("Bestie", "incoming", 0x50000001u);
+        chat.OnSelfSent(ChatKind.Tell, "outgoing", "Caith");
+
+        targets.ResetSession();
+
+        Assert.Null(targets.LastIncomingTellSender);
+        Assert.Null(targets.LastOutgoingTellTarget);
+        Assert.Equal(2, chat.Count);
+    }
+
+    [Fact]
+    public void DisposeDetachesAndIsIdempotent()
+    {
+        var chat = new ChatLog();
+        var targets = new ChatCommandTargetState(chat);
+
+        targets.Dispose();
+        targets.Dispose();
+        chat.OnTellReceived("After", "ignored", 0x50000002u);
+
+        Assert.Null(targets.LastIncomingTellSender);
+        Assert.Null(targets.LastOutgoingTellTarget);
+    }
+}