APX Memory Compaction Is Two Knobs, Not One

APX Memory Compaction uses two knobs: compact_threshold and keep_recent. compact_threshold decides when compression starts, while keep_recent decides how much of the newest work stays verbatim. Setting keep_recent too close to compact_threshold can disable the useful part of the system. A sane rule is to keep keep_recent clearly below compact_threshold. The default configuration is { "memory": { "compact_threshold": 60, "keep_recent": 40 } }.