anchored-iterative-merge-prevents-compaction-drift

On subsequent compactions of a long session, summarizing only the delta since the last compaction and merging into existing sections (rather than regenerating the full summary) prevents cumulative drift. Full regeneration treats each compaction as a fresh summarization, causing ‘low-priority’ details to be dropped each cycle. The anchor is the surviving section from the prior compaction — it is not re-summarized, only new content is processed and merged in.