Root cause bugs fixed in local echo overlay:
1. Stored flushed text as string (_flushedText, _flushedTexts Map) to avoid reading stale terminal buffer
2. Overlay stays visible when pendingText empties but flushed > 0
3. Backspace into flushed text has immediate visual feedback
4. _flushedTexts.delete() added alongside _flushedOffsets.delete() in Enter/Ctrl+C/cleanup
5. OSC terminal responses (xterm color queries) no longer clear flushed text state —
was triggered by _handleColorEvent → triggerDataEvent during buffer load after tab switch
Added comprehensive test suite (test/local-echo-user-test.mjs): 39 tests across 9 groups
including line wrapping, tab switch round-trips, backspace into flushed text, and more.
All 6 test suites pass (133 total assertions).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
