fix(config): deep-clone UsedChannel and TellTarget in Tab.Clone

Cherry-pick from ChatTwo upstream f35b7d3 (Infiziert90, 2026-05-12).

Tab.Clone() used to assign CurrentChannel = CurrentChannel and run
TellTarget.From(TellTarget). The first was a plain reference copy of
the UsedChannel — the clone and the source shared the same channel
state, so a channel switch or TellTarget update on a PopOut/Temp tab
also mutated its origin tab. The second was a static factory call
that read like a constructor where every other place uses Clone().

- TellTarget: static From(t) replaced by instance Clone(); only
  call-site swapped to TellTarget.Clone().
- UsedChannel: new Clone() that copies the scalar fields and runs
  Clone() on the two TellTarget references (null-safe).
- Tab.Clone(): CurrentChannel goes through UsedChannel.Clone().

HellionChat/Configuration.cs

@@ -500,7 +500,7 @@ public class Tab
             Opacity = Opacity,
             Identifier = Identifier,
             InputDisabled = InputDisabled,
-            CurrentChannel = CurrentChannel,
+            CurrentChannel = CurrentChannel.Clone(),
             CanMove = CanMove,
             CanResize = CanResize,
             IndependentHide = IndependentHide,
@@ -512,7 +512,7 @@ public class Tab
             HideWhenInactive = HideWhenInactive,
             IsTempTab = IsTempTab,
             AllSenderMessages = AllSenderMessages,
-            TellTarget = TellTarget.From(TellTarget),
+            TellTarget = TellTarget.Clone(),
             IsGreeted = IsGreeted,
         };
     }
@@ -690,6 +690,29 @@ public class UsedChannel
     {
         Channel = channel;
     }
+
+    // ---------------------------------------------------------------
+    // Cherry-picked from ChatTwo upstream f35b7d3 (Infiziert90, 2026-05-12)
+    // - Deep-clone the UsedChannel so Tab.Clone() no longer shares
+    //   channel state (incl. TellTarget) with its origin Tab. Previously
+    //   a reference copy: PopOut and Temp tabs mutated each other.
+    // - Name is intentionally a reference copy (matches upstream); it
+    //   gets reassigned on every channel switch anyway.
+    // TEST-MIRROR: ../../Hellion Build test/_Helpers/UsedChannelCloneTests.cs
+    // ---------------------------------------------------------------
+    public UsedChannel Clone()
+    {
+        return new UsedChannel
+        {
+            Channel = Channel,
+            Name = Name,
+            TellTarget = TellTarget?.Clone(),
+
+            UseTempChannel = UseTempChannel,
+            TempChannel = TempChannel,
+            TempTellTarget = TempTellTarget?.Clone(),
+        };
+    }
 }
 
 [Serializable]

HellionChat/GameFunctions/Types/TellTarget.cs

@@ -40,5 +40,11 @@ public class TellTarget
 
     public static TellTarget Empty() => new(string.Empty, 0, 0, TellReason.Direct);
 
-    public static TellTarget From(TellTarget t) => new(t.Name, t.World, t.ContentId, t.Reason);
+    // ---------------------------------------------------------------
+    // Cherry-picked from ChatTwo upstream f35b7d3 (Infiziert90, 2026-05-12)
+    // - Replaced static From(t) with an instance-style Clone() so call
+    //   sites read like a copy operation, not a factory.
+    // TEST-MIRROR: ../../../Hellion Build test/_Helpers/TellTargetCloneTests.cs
+    // ---------------------------------------------------------------
+    public TellTarget Clone() => new(Name, World, ContentId, Reason);
 }