fix(terminal): settle the edit-sync diff at the next keydown so Enter cannot erase the line (#541 review)

A pending 229 edit plus Enter in one page task: xterm clears the textarea for CR before the edit timer runs, so the timer diffed the whole line against '' and sent one DEL per character ahead of the submitted line. The pending diff is now applied synchronously from handleKeyEvent, before flushPending() (which keeps the orphan candidate from sending the character twice).

Tests: unit (3) and browser (4, local echo on and off, plain last character and autocorrect), each verified to fail without the settle call. xterm-private-api guard now names the CompositionHelper fields this depends on and checks the shipped bundle; CLAUDE.md notes the edit-based 229 diff.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JrzFKEdBLwVfu6ev2ZscJS

test/terminal-keycode229-recovery.test.ts

@@ -520,6 +520,57 @@ describe('edit-based sync of the helper textarea (autocorrect replacements)', ()
     h.flush();
   };
 
+  // The batched Android shape (#441): the last character's keydown and `insertText` arrive in the
+  // SAME page task as Enter's keydown. xterm's own Enter handling clears the textarea before the
+  // edit's timer runs, so a timer left pending would diff the whole line against '' and send one
+  // DEL per character AHEAD of the submitted line. The edit is therefore settled at the next
+  // keydown, before xterm sees that key.
+  it('settles a pending edit at the next keydown, so Enter in the same task cannot erase the line', () => {
+    const h = editSyncHarness();
+    const controller = h.create(true);
+    typeKeys(h, 'hell');
+    h.keydown();
+    h.edit('hello');
+    controller.handleKeyEvent({ type: 'keydown', key: 'Enter', keyCode: 13 });
+    h.textarea.value = ''; // xterm's CR handling, which runs after the custom key handler
+    h.flush();
+    expect(h.sent.join('')).toBe('hello');
+    expect(h.sent).not.toContain('\x7f');
+  });
+
+  it('autocorrect and Enter in one task submits the corrected line, not a run of DELs', () => {
+    const h = editSyncHarness();
+    const controller = h.create(true);
+    typeKeys(h, 'testing the peompt');
+    h.keydown();
+    h.edit('testing the p');
+    h.keydown();
+    h.edit('testing the prompt ');
+    controller.handleKeyEvent({ type: 'keydown', key: 'Enter', keyCode: 13 });
+    h.textarea.value = '';
+    h.flush();
+    expect(h.line()).toBe('testing the prompt ');
+    expect(h.sent.filter((c) => c === '\x7f')).toHaveLength(5); // the five deleted characters, nothing more
+  });
+
+  it('settling first stands the same keystroke’s orphan candidate down (no double send)', () => {
+    const h = editSyncHarness();
+    const controller = h.create(true);
+    // xterm's canonical-data hook, as terminal-ui.js wires it.
+    const origTrigger = h.helper._coreService.triggerDataEvent;
+    h.helper._coreService.triggerDataEvent = (data: string) => {
+      origTrigger(data);
+      controller.notifyCanonicalData();
+    };
+    controller.handleKeyEvent({ type: 'keydown', key: 'Unidentified', keyCode: 229 });
+    h.keydown();
+    h.edit('o');
+    h.textarea.fire('input', inputEvent('o'));
+    controller.handleKeyEvent({ type: 'keydown', key: 'Enter', keyCode: 13 });
+    h.flush();
+    expect(h.sent.join('')).toBe('o');
+  });
+
   it('control: xterm alone duplicates the line when the keyboard autocorrects', () => {
     const h = editSyncHarness();
     h.create(false);