After a whole sheet is 完成, clicking 开始生成 silently shows '0 待处理 /
完成 0' and also re-empties the preview sample dropdown. Document two fixes:
(1) a clear 'no pending rows' message (N done skipped / M failed retryable /
clear E column to redo), (2) _on_tasks_loaded must not reset the preview combo
(read_all_rows owns it). Add §10.4 + §19.10.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>