test(terminal): guard the xterm mouse-service privates touch forwarding reads

Merge-time fix for #664: _shouldForwardTouchToApp reads
terminal._core.coreMouseService.activeEncoding, an xterm private. The
bundle-string loop in test/xterm-private-api.test.ts now checks
coreMouseService and activeEncoding too, and both failure messages name
_shouldForwardTouchToApp, so an xterm upgrade that renames either field
cannot silently stop touch forwarding to native SGR tracking apps.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

test/xterm-private-api.test.ts

@@ -49,8 +49,10 @@ describe('xterm private-API dependency guard', () => {
       'xterm moved off the verified version — re-verify _kickRenderer in a real browser ' +
         '(terminal-ui.js: _core._renderService._renderDebouncer._animationFrame) AND the ' +
         'CompositionHelper fields installEditSync() uses (terminal-keycode229-recovery.js: ' +
-        '_handleAnyTextareaChanges, _coreService, _isComposing, _isSendingComposition, _dataAlreadySent), ' +
-        'then update VERIFIED_XTERM_VERSION here. The accessor is optional-chained, so a renamed field ' +
+        '_handleAnyTextareaChanges, _coreService, _isComposing, _isSendingComposition, _dataAlreadySent) ' +
+        'and the mouse-encoding read _shouldForwardTouchToApp makes (terminal-ui.js: ' +
+        '_core.coreMouseService.activeEncoding), then update VERIFIED_XTERM_VERSION here. ' +
+        'The accessor is optional-chained, so a renamed field ' +
         'degrades to a silent no-op and the freeze it heals comes back unnoticed.'
     ).toBe(VERIFIED_XTERM_VERSION);
   });
@@ -60,9 +62,12 @@ describe('xterm private-API dependency guard', () => {
   // append-only diff duplicates). It reaches `_compositionHelper`, `_coreService`, `_isComposing`,
   // `_isSendingComposition` and `_dataAlreadySent`; if xterm renames any of them the install quietly
   // falls back to xterm's own handler and the duplication returns (or, for `_isSendingComposition`, a
-  // composition xterm finalizes at an Enter keydown is sent twice). Property names survive
+  // composition xterm finalizes at an Enter keydown is sent twice). terminal-ui.js's
+  // _shouldForwardTouchToApp reads `_core.coreMouseService.activeEncoding` to forward a touch drag
+  // only to an app that asked for SGR mouse reports; if either name changes the read is undefined
+  // and touch quietly stops forwarding to native SGR tracking apps. Property names survive
   // minification, so a string check on the shipped bundle catches a rename on upgrade.
-  it('still ships the composition-helper fields the edit-based 229 sync depends on', () => {
+  it('still ships the composition-helper and mouse-service fields terminal input depends on', () => {
     const bundle = readFileSync(resolve(root, 'node_modules/@xterm/xterm/lib/xterm.js'), 'utf8');
     for (const name of [
       '_handleAnyTextareaChanges',
@@ -71,11 +76,14 @@ describe('xterm private-API dependency guard', () => {
       '_isComposing',
       '_isSendingComposition',
       '_dataAlreadySent',
+      'coreMouseService',
+      'activeEncoding',
     ]) {
       expect(
         bundle,
         `xterm no longer mentions ${name}: re-verify terminal-keycode229-recovery.js installEditSync() ` +
-          '(src/web/public) against the new CompositionHelper before bumping VERIFIED_XTERM_VERSION'
+          'against the new CompositionHelper, and terminal-ui.js _shouldForwardTouchToApp against the ' +
+          'new CoreMouseService (both in src/web/public), before bumping VERIFIED_XTERM_VERSION'
       ).toContain(name);
     }
   });