Nuum incremental distillation and evaluation lessons

Trigger backgroundDistill after storing a completed assistant message when undistilled count reaches config.distillation.maxSegment (default 50); retain session.idle as catchall. Historical sessions require explicit backfill. The distillation prompt must capture every assistant-generated item, preserve numbered ordering, and retain distinguishing quantities, ratios, temperatures, names, locations, and prices. Under-capture caused single-session-assistant accuracy to fall from 83.9% to 57.1%; explicit rules/examples raised it to 96.4%. LongMemEval improved from 72.6% baseline to 88.0% final, and coding evaluation from 10/15 to 14/15. Prioritize incremental batches, prompt coverage, then cross-session entity merging.