With StaComThread's GetMessage loop in place, OnWriteComplete callbacks are now delivered properly. Write flow: dispatch Write() on STA thread, await OnWriteComplete via TCS, clean up on STA thread. Falls back to fire-and-forget on timeout as safety net. OnWriteComplete now resolves or rejects the TCS with MxStatus error details. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>