fix(tell): strip stale tell state on tab activation

OnTabActivated clears the runtime tell state the game-side detour leaves on a tab (CurrentChannel tell target + partner label) when a DIFFERENT tab becomes the input surface, so a normal typed line can no longer route as a silent /tell to the old partner. Re-clicking the active tab and tabs carrying their own Tab.TellTarget binding (leg1) are preserved.

All four activation paths route through it: Sidebar, TopTabBar, ChannelPopoutPool.TryOpen, and the MainWindow draw-seed. EnsureCurrentChannel becomes a pure derive-helper reached only via OnTabActivated. Adds the TellResetOnActivateStep self-test (step count 29 -> 30).

HellionChat/Ui/Components/Sidebar.cs

@@ -247,8 +247,9 @@ internal sealed class Sidebar
         var rowHovered = ImGui.IsItemHovered();
         if (ImGui.IsItemClicked())
         {
+            var previous = activeTab;
             activeTab = tab;
-            TabLifecycleHelpers.EnsureCurrentChannel(tab);
+            TabLifecycleHelpers.OnTabActivated(tab, previous);
         }
 
         dl.DrawHoverSheen(

HellionChat/Ui/Components/TopTabBar.cs

@@ -34,8 +34,9 @@ internal sealed class TopTabBar
                 )
             )
             {
+                var previous = activeTab;
                 activeTab = tab;
-                TabLifecycleHelpers.EnsureCurrentChannel(tab);
+                TabLifecycleHelpers.OnTabActivated(tab, previous);
             }
 
             TabContextMenu.Draw(tab, $"toptab_ctx_{i}", _pool);

HellionChat/Ui/Windows/ChannelPopoutPool.cs

@@ -1,3 +1,4 @@
+using HellionChat.Util;
 using Microsoft.Extensions.Logging;
 
 namespace HellionChat.Ui.Windows;
@@ -40,6 +41,12 @@ internal sealed class ChannelPopoutPool
 
     public bool TryOpen(Tab tab)
     {
+        // A popped tab gets its own input bar, so strip stale tell state first —
+        // otherwise a popped-out stale-tell tab would be a send surface that
+        // bypasses the click-path activation strip. Previous = the main window's
+        // active tab; popping the active tab itself must not strip (TR-4 guard).
+        TabLifecycleHelpers.OnTabActivated(tab, Plugin.Instance.MainWindow?.ActiveTab);
+
         var slot = _slots.TryReserve(tab.Identifier);
         if (slot < 0)
         {

HellionChat/Ui/Windows/MainWindow.cs

@@ -156,7 +156,13 @@ internal sealed class MainWindow : Window
         // First-frame seed: the active tab defaults to the first persisted
         // tab so the message list isn't empty on a clean session.
         if (_activeTab is null && Plugin.Config.Tabs.Count > 0)
-            _activeTab = Plugin.Config.Tabs[0];
+        {
+            var seeded = Plugin.Config.Tabs[0];
+            _activeTab = seeded;
+            // The seeded Tabs[0] is the likeliest legacy stale-tell carrier
+            // (pre-coupling the detour wrote here); strip it like any activation.
+            TabLifecycleHelpers.OnTabActivated(seeded, null);
+        }
 
         var statusHeight = Components.StatusBar.Height;