feat: add bounded npc memory retention

docs/PROJECT_CONTEXT.md

@@ -415,8 +415,8 @@ Focused `RefCounted` collaborators keep rule ownership visible:
   village resource views;
 - `SimulationEventLog` owns deterministic event history and queries;
 - `EventKnowledgeSystem` owns per-NPC known-event references, immutable
-  first-acquisition provenance, actor/nearby evidence capture, and bounded
-  one-hop communication;
+  first-acquisition time/provenance, actor/nearby evidence capture, bounded
+  one-hop communication, and deterministic recent-memory retention;
 - `RelationshipSystem` owns directed relationship state, event-driven trust
   consequences, and deterministic social queries.
 
@@ -523,7 +523,7 @@ NpcVisual navigates through the active world
 │   ├── definitions/           Stable IDs and custom definition resources
 │   ├── economy/               Inventory and storage transactions
 │   ├── events/                Ordered event history and queries
-│   ├── knowledge/             Per-NPC facts, provenance, and bounded transfer
+│   ├── knowledge/             Per-NPC facts, provenance, transfer, and retention
 │   ├── persistence/           Validated local save-slot storage
 │   ├── relationships/         Directed social consequences and queries
 │   └── state/                 Versioned simulation-state records
@@ -533,6 +533,7 @@ NpcVisual navigates through the active world
 │   ├── deterministic_simulation_test.gd
 │   ├── food_storage_loop_test.gd
 │   ├── jajce_world_scaffold_test.gd
+│   ├── knowledge_retention_consequence_test.gd
 │   ├── jajce_runtime_integration_test.gd
 │   ├── npc_visual_lifecycle_test.gd
 │   ├── relationship_consequence_test.gd
@@ -571,7 +572,7 @@ These are expected prototype constraints, not necessarily isolated bugs:
   gathering use `ResourceNode` instances with no fallback, food transfer uses
   the typed pantry `StorageNode`, and patrol/study/rest use `ActivitySite`.
 - Current NPC, village, resource, storage, event, knowledge, relationship,
-  clock, and RNG state serialize through world schema v6. F5/F9 provide one
+  clock, and RNG state serialize through world schema v7. F5/F9 provide one
   validated local quicksave; a save menu, metadata, and player-transform
   persistence remain deferred.
 - Simulation-owned resource records retain live amounts, reservations, and
@@ -586,12 +587,14 @@ These are expected prototype constraints, not necessarily isolated bugs:
   located items.
 - NPCs have home positions, schedule periods, carried food/wood, and directed
   familiarity/trust. They retain direct or one-hop communicated knowledge of a
-  food deposit with first-acquisition provenance, but do not yet have wider
-  social dimensions, goals, line-of-sight/hearing evidence, importance/decay,
-  false beliefs, or multi-hop rumours.
+  food deposit with first-acquisition provenance. Current trust causes are
+  lasting; other knowledge is capped and reviewed after one simulated day.
+  NPCs do not yet have wider social dimensions, goals, line-of-sight/hearing
+  evidence, personalized reinforcement/decay, false beliefs, or multi-hop
+  rumours.
 - The reason inspector exposes current decisions, utility rejections, one exact
-  relationship cause, and the latest known fact with its speaker when
-  communicated, but deeper historical decision traces are not yet retained.
+  relationship cause, memory counts, and the latest known fact with its speaker
+  and retention class, but a broader person-history view is not yet present.
 - Active navigation is used as if all agents are local; no simulation LOD exists.
 - Unloaded traveling NPCs preserve their state but do not yet advance through
   abstract travel time.
@@ -836,7 +839,10 @@ shared non-storage activity, an already-working direct knower can tell one fact
 to an arriving nearby villager. The same event remains visible as known fact
 and relationship cause, the inspector names the speaker, and the listener's
 future work can change without duplicating event history. Importance and
-retention for known facts is the next systems slice.
+retention now keep current relationship causes lasting, cap other memories,
+and forget routine facts at deterministic daily-sized reviews without deleting
+the objective event. A compact retained-memory/person-history view and visible
+social-reaction cue are the next systems slice.
 
 The remaining simulation-garden target still aims for: