Compaction

Compaction is summarising a conversation that is nearing the window limit and reinitiating a fresh one from the summary. Anthropic calls it the first lever for long-term coherence; Claude Code's version keeps architectural decisions, unresolved bugs and implementation details while dropping redundant tool output. The hard part is selection, and Anthropic says so directly — aggressive compaction loses context whose importance only becomes clear later. The corollary engineers keep relearning expensively is that conversation is exactly what compaction eats, so anything load-bearing has to live in a file the agent will read back.