feat(ipc): mirror context-menu IPC gates under ChatTwo namespace (v1.4.9 R4 ext)

Extends commit 8c4afaa: the TypingIpc mirror covered only two of the six
ChatTwo IPC slots. Third-party plugins like Artisan and AllaganTools
subscribe to a different ChatTwo IPC surface — the context-menu
integration (ChatTwo.Register / Unregister / Available / Invoke) that
lets them push item-links into the chat. Smoke test against the
deployed v1.4.9 build showed Artisan logging "Chat2 is not available"
because those four gates were not yet mirrored.

This commit adds the missing four ChatTwo-prefixed provider gates in
IpcManager.cs:

- ChatTwo.Register  (Func<string>) — bound to the existing Register()
  backing method, so plugins that subscribe via either namespace land
  in the same Registered list.
- ChatTwo.Unregister (Action<string>) — bound to the existing
  Unregister() backing method, same shared-state rationale.
- ChatTwo.Available (Action<>) — SendMessage() fires from the ctor right
  after AvailableGate.SendMessage(), so any subscriber waiting on the
  "Chat 2 became available" signal sees both events.
- ChatTwo.Invoke (Action<string, PlayerPayload?, ulong, Payload?,
  SeString?, SeString?>) — Invoke() fans the context-menu event out to
  both InvokeGate and ChatTwoInvokeGate in lockstep. Subscribers compare
  on the registration ID they got back from Register, so the
  shared-backing approach keeps that contract intact regardless of which
  namespace they subscribed under.

Dispose() unregisters all four ChatTwo gates plus the four existing
HellionChat gates. The conflict-detection that prevents ChatTwo from
loading alongside HellionChat guarantees no slot collision at runtime.

With this commit the full ChatTwo IPC surface (6 of 6 slots) is mirrored:
- ChatTwo.GetChatInputState     (TypingIpc, commit 8c4afaa)
- ChatTwo.ChatInputStateChanged (TypingIpc, commit 8c4afaa)
- ChatTwo.Register              (IpcManager, this commit)
- ChatTwo.Unregister            (IpcManager, this commit)
- ChatTwo.Available             (IpcManager, this commit)
- ChatTwo.Invoke                (IpcManager, this commit)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

HellionChat/IpcManager.cs

@@ -19,6 +19,26 @@ internal sealed class IpcManager : IDisposable
         object?
     > InvokeGate { get; }
 
+    // v1.4.9 R4: ChatTwo IPC compatibility mirror. Third-party plugins with
+    // a no-fork policy (e.g. Artisan, AllaganTools) only subscribe to the
+    // ChatTwo.*-prefixed context-menu integration gates. Mirroring all four
+    // provider slots under the ChatTwo namespace lets those plugins keep
+    // working without code changes on their side. Conflict detection
+    // prevents ChatTwo and HellionChat from loading in parallel, so no slot
+    // collision risk.
+    private ICallGateProvider<string> ChatTwoRegisterGate { get; }
+    private ICallGateProvider<string, object?> ChatTwoUnregisterGate { get; }
+    private ICallGateProvider<object?> ChatTwoAvailableGate { get; }
+    private ICallGateProvider<
+        string,
+        PlayerPayload?,
+        ulong,
+        Payload?,
+        SeString?,
+        SeString?,
+        object?
+    > ChatTwoInvokeGate { get; }
+
     internal List<string> Registered { get; } = [];
 
     public IpcManager()
@@ -41,7 +61,32 @@ internal sealed class IpcManager : IDisposable
             object?
         >("HellionChat.Invoke");
 
+        // v1.4.9 R4: ChatTwo-prefixed mirrors of the four context-menu slots
+        // above. Share the same Register/Unregister backing methods so a
+        // plugin that subscribes via either namespace lands in the same
+        // Registered list. SendMessage on Invoke fans out to both gates.
+        ChatTwoRegisterGate = Plugin.Interface.GetIpcProvider<string>("ChatTwo.Register");
+        ChatTwoRegisterGate.RegisterFunc(Register);
+
+        ChatTwoAvailableGate = Plugin.Interface.GetIpcProvider<object?>("ChatTwo.Available");
+
+        ChatTwoUnregisterGate = Plugin.Interface.GetIpcProvider<string, object?>(
+            "ChatTwo.Unregister"
+        );
+        ChatTwoUnregisterGate.RegisterAction(Unregister);
+
+        ChatTwoInvokeGate = Plugin.Interface.GetIpcProvider<
+            string,
+            PlayerPayload?,
+            ulong,
+            Payload?,
+            SeString?,
+            SeString?,
+            object?
+        >("ChatTwo.Invoke");
+
         AvailableGate.SendMessage();
+        ChatTwoAvailableGate.SendMessage();
     }
 
     internal void Invoke(
@@ -54,6 +99,8 @@ internal sealed class IpcManager : IDisposable
     )
     {
         InvokeGate.SendMessage(id, sender, contentId, payload, senderString, content);
+        // v1.4.9 R4: fan out the same event to plugins listening on ChatTwo.Invoke.
+        ChatTwoInvokeGate.SendMessage(id, sender, contentId, payload, senderString, content);
     }
 
     private string Register()
@@ -72,6 +119,8 @@ internal sealed class IpcManager : IDisposable
     {
         UnregisterGate.UnregisterAction();
         RegisterGate.UnregisterFunc();
+        ChatTwoUnregisterGate.UnregisterAction();
+        ChatTwoRegisterGate.UnregisterFunc();
         Registered.Clear();
     }
 }