refactor(ipc): drop this.-qualifier and trim BuildState comments

Same shadowing-via-instance-property as Plugin.CurrentTab above. Comments
trimmed to default 1-3 line density; security/threading WHY-blocks earn
their lines when they document non-obvious invariants, not standard C#
name resolution.

HellionChat/Ipc/TypingIpc.cs

@@ -70,30 +70,13 @@ internal sealed class TypingIpc : IDisposable
             : usedChannel.Channel;
         var channelType = inputChannel.ToChatType();
 
-        // `Plugin` here is the instance property on TypingIpc (TypingIpc.cs:18
+        // MainWindow is Phase-1-resolved and never reassigned;
-        // `private Plugin Plugin { get; }`), NOT the type `HellionChat.Plugin`.
+        // the `?.` is defense-in-depth for pre-Phase-1 IPC-pulls.
-        // C# resolves `Plugin.MainWindow` as `this.Plugin.MainWindow` because
+        var mainWindowOpen = Plugin.MainWindow?.IsOpen ?? false;
-        // the instance property shadows the type name inside this class. Do
-        // NOT switch to a type-qualified read (CS0120 — `MainWindow` is an
-        // instance member, not a static one). MainWindow is resolved in Phase-1
-        // (Plugin.cs:295) and never re-assigned, so `this.Plugin.MainWindow`
-        // is non-null by the time TypingIpc.Update() runs (HostedServices only
-        // start after Phase-1). The `null!`-suppression on the MainWindow
-        // property would let us drop the `?.`, but a null-safe read costs
-        // nothing at runtime and shields against a theoretical pre-Phase-1
-        // caller (a future IPC-pull that fires before HostedServices start).
-        // Defense in depth, no behaviour change for the production path.
-        var mainWindowOpen = this.Plugin.MainWindow?.IsOpen ?? false;
 
-        // Stale-state guard: InputBar._isFocused is only written in DrawInputField,
+        // Stale-state guard: InputBar's focus and pending-buffer fields are
-        // which only runs while MainWindow is open. After the user closes the
+        // only written by DrawInputField. Closing MainWindow freezes them, so
-        // window, _isFocused freezes on the last value. _pendingMessage has the
+        // gate all four state fields on mainWindowOpen.
-        // same stale problem — it is only cleared in TrySend (successful send)
-        // or ClearBuffer (manual reset), so closing MainWindow with non-empty
-        // buffer leaves PendingLength frozen above zero. Without gating all
-        // four state fields on mainWindowOpen, Cross-Plugin-Subscribers would
-        // keep seeing InputFocused: true / HasText: true / IsTyping: true /
-        // TextLength: N even though no input field exists.
         var inputFocused = mainWindowOpen && _inputBar.IsFocused;
         var hasText = mainWindowOpen && _inputBar.PendingLength > 0;
         var textLength = mainWindowOpen ? _inputBar.PendingLength : 0;