feat: add bounded npc memory retention

simulation/SimulationManager.gd

@@ -17,6 +17,7 @@ signal npc_decision_recorded(npc: SimNPC, decision: ActionSelectionResult)
 signal relationship_changed(relationship: RelationshipStateRecord, cause_event: EconomicEventRecord)
 signal event_knowledge_changed(knower_id: int, event: EconomicEventRecord)
 signal event_knowledge_transferred(speaker_id: int, listener_id: int, event: EconomicEventRecord)
+signal event_knowledge_forgotten(knower_id: int, event: EconomicEventRecord)
 
 var village := SimVillage.new()
 
@@ -158,6 +159,8 @@ func simulate_tick() -> void:
 
 	if village_was_changed:
 		village_changed.emit(village)
+	if tick_count % get_knowledge_review_interval() == 0:
+		_maintain_event_knowledge(true)
 
 	if debug_logs:
 		print(village.get_summary())
@@ -600,13 +603,15 @@ func try_communicate_at_shared_activity(speaker_id: int, listener_id: int) -> bo
 	var listener := _find_npc_by_id(listener_id)
 	if not _can_communicate_at_shared_activity(speaker, listener):
 		return false
-	var known_event_ids := event_knowledge_system.get_known_event_ids(speaker.id, 0)
-	for index in range(known_event_ids.size() - 1, -1, -1):
-		var event := event_log.get_by_id(known_event_ids[index])
+	var known_event_ids := event_knowledge_system.get_communicable_event_ids(
+		speaker.id, _get_lasting_event_ids(speaker.id)
+	)
+	for event_id in known_event_ids:
+		var event := event_log.get_by_id(event_id)
 		if event == null:
 			continue
 		var learned_record := event_knowledge_system.communicate_event(
-			event, speaker.id, listener.id
+			event, speaker.id, listener.id, tick_count
 		)
 		if learned_record == null:
 			continue
@@ -648,13 +653,51 @@ func _can_communicate_at_shared_activity(speaker: SimNPC, listener: SimNPC) -> b
 func _apply_new_event_knowledge(
 	known_event: KnownEventStateRecord, event: EconomicEventRecord
 ) -> void:
-	event_knowledge_changed.emit(known_event.get_knower_id(), event)
 	var newly_informed_ids: Array[int] = [known_event.get_knower_id()]
 	var changed_relationships: Array[RelationshipStateRecord] = relationship_system.apply_event(
 		event, npcs, newly_informed_ids
 	)
+	event_knowledge_changed.emit(known_event.get_knower_id(), event)
 	for relationship in changed_relationships:
 		relationship_changed.emit(relationship, event)
+	_maintain_event_knowledge(false)
+
+
+func _maintain_event_knowledge(expire_by_age: bool) -> void:
+	var forgotten := event_knowledge_system.maintain_retention(
+		tick_count, get_knowledge_review_interval(), _get_lasting_knowledge_records(), expire_by_age
+	)
+	for known_event in forgotten:
+		var event := event_log.get_by_id(known_event.get_event_id())
+		if event != null:
+			event_knowledge_forgotten.emit(known_event.get_knower_id(), event)
+
+
+func _get_lasting_knowledge_records() -> Array[KnownEventStateRecord]:
+	var lasting: Array[KnownEventStateRecord] = []
+	var seen := {}
+	for relationship in relationship_system.get_all_sorted():
+		var event_id := relationship.get_last_trust_cause_event_id()
+		if event_id == RelationshipStateRecord.NO_CAUSE_EVENT:
+			continue
+		var record := event_knowledge_system.get_record(relationship.get_observer_id(), event_id)
+		if record == null:
+			continue
+		var key := "%d:%d" % [record.get_knower_id(), record.get_event_id()]
+		if seen.has(key):
+			continue
+		seen[key] = true
+		lasting.append(record)
+	return lasting
+
+
+func _get_lasting_event_ids(npc_id: int) -> Array[int]:
+	var event_ids: Array[int] = []
+	for record in _get_lasting_knowledge_records():
+		if record.get_knower_id() == npc_id:
+			event_ids.append(record.get_event_id())
+	event_ids.sort()
+	return event_ids
 
 
 func _find_npc_by_id(npc_id: int) -> SimNPC:
@@ -695,6 +738,24 @@ func get_known_event_record(npc_id: int, event_id: int) -> KnownEventStateRecord
 	return event_knowledge_system.get_record(npc_id, event_id)
 
 
+func is_known_event_lasting(npc_id: int, event_id: int) -> bool:
+	return event_id in _get_lasting_event_ids(npc_id)
+
+
+func get_memory_summary(npc_id: int) -> Dictionary:
+	var total := event_knowledge_system.get_known_event_ids(npc_id, 0).size()
+	var lasting := _get_lasting_event_ids(npc_id).size()
+	return {"lasting": lasting, "recent": maxi(total - lasting, 0)}
+
+
+func get_knowledge_review_interval() -> int:
+	var active_cycle_duration := (
+		clock.cycle_duration_seconds if clock != null else cycle_duration_seconds
+	)
+	var active_tick_interval := clock.tick_interval if clock != null else tick_interval
+	return maxi(roundi(active_cycle_duration / maxf(active_tick_interval, 0.0001)), 1)
+
+
 func get_current_speed() -> String:
 	return "%.2fx" % SPEED_LEVELS[speed_index]
 
@@ -1018,6 +1079,7 @@ func restore_state(record: SimulationStateRecord) -> bool:
 		npcs.append(npc_record.restore(debug_logs))
 	relationship_system.restore(record.relationships)
 	event_knowledge_system.restore(record.event_knowledge)
+	_maintain_event_knowledge(tick_count % get_knowledge_review_interval() == 0)
 
 	wander_random_sources.clear()
 	var wander_streams: Array = record.simulation["wander_random_streams"]