feat: add bounded npc memory retention

docs/BUILD_IN_PUBLIC_PLAN.md

@@ -695,11 +695,16 @@ Completed:
     can hear one direct fact from a nearby worker at the same non-storage
     activity; the inspector names the speaker, the original event is not
     replayed, and heard facts do not cascade yet.
+23. Bounded memory retention: acquisition time now drives fact recency; current
+    relationship causes remain lasting while each NPC keeps only three other
+    recent facts. A deterministic daily-sized review fades old routine facts,
+    conversations prefer lasting evidence, and the inspector shows both memory
+    counts and the displayed fact's retention class.
 
 Next:
 
-1. Add bounded importance/retention rules for known facts, as sequenced in
-   `LEARNING_ROADMAP.md`.
+1. Add a compact retained-memory/person-history view and one visible social
+   reaction cue, as sequenced in `LEARNING_ROADMAP.md`.
 
 Do not start with GIS data, a full city, a large asset pack, or more NPC
 mechanics. The next proof is a beautiful stage for the systems that already