fix: iOS Safari Chinese punctuation input not working

Fix input handling for Chinese punctuation (，。！？) and spaces on iOS Safari.

The issue occurs because:
1. iOS Safari fires keydown (setting _keyDownSeen=true)
2. Then fires input event with ev.composed=true
3. But NO composition events are triggered for punctuation

The old condition `(!ev.composed || !this._keyDownSeen)` would reject these
inputs because both conditions are true.

The fix changes the condition to check `!this._compositionHelper.isComposing`
instead. This correctly:
- Accepts punctuation input (not composing, so we handle it)
- Rejects input during actual composition (CompositionHelper handles it)
- Prevents emoji duplication (emoji goes through composition flow)

Fixes #3070, #4486

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: mylukin

src/browser/CoreBrowserTerminal.ts

@@ -1241,10 +1241,13 @@ export class CoreBrowserTerminal extends CoreTerminal implements ITerminal {
    * @param ev The input event to be handled.
    */
   protected _inputEvent(ev: InputEvent): boolean {
-    // Only support emoji IMEs when screen reader mode is disabled as the event must bubble up to
-    // support reading out character input which can doubling up input characters
-    // Based on these event traces: https://github.com/xtermjs/xterm.js/issues/3679
-    if (ev.data && ev.inputType === 'insertText' && (!ev.composed || !this._keyDownSeen) && !this.optionsService.rawOptions.screenReaderMode) {
+    // Handle direct text input (not from composition).
+    // When composing (e.g., emoji picker, CJK IME), the CompositionHelper handles input via
+    // compositionend event. We skip input events during composition to prevent duplicates.
+    // When NOT composing, we accept input events even if ev.composed=true, which fixes
+    // iOS Safari Chinese punctuation input (issue #3070, #4486).
+    // Screen reader mode needs the event to bubble for accessibility announcements.
+    if (ev.data && ev.inputType === 'insertText' && !this._compositionHelper!.isComposing && !this.optionsService.rawOptions.screenReaderMode) {
       if (this._keyPressHandled) {
         return false;
       }