Nice architecture. The hot/warm/cold tiering with markdown-only storage is elegant with zero dependencies is a strong design choice.
One thing I've noticed building persistent agents: purely factual memory misses something important. Two memories can have the same content but very different significance depending on the emotional context when they were formed. A conversation about "work" during a stressful moment is fundamentally different from the same topic during a relaxed one.
Curious whether your compaction tree preserves any contextual weight during compression, or if all memories are treated equally in the hierarchy.