docs: mark simulation architecture gate complete

- Update ACTION_SYSTEM_ARCHITECTURE.md to describe the active-position
  contract and visual lifecycle proof
- Mark BUILD_IN_PUBLIC_PLAN.md systems-gate section complete
- Mark LEARNING_ROADMAP.md architecture-gate section complete and
  renumber post-gate implementation sequence
- Update PROJECT_CONTEXT.md immediate-milestone section to reflect
  completed gate and next food-loop milestone
- Update SIMULATION_STATE_SCHEMA.md with NPCStateRecord v2 details
- Update ADR 0001 checklist to mark active-position sync done

docs/PROJECT_CONTEXT.md

@@ -469,6 +469,7 @@ NpcVisual navigates through the active world
 │   ├── deterministic_simulation_test.gd
 │   ├── flat_map_baseline_test.gd
 │   ├── jajce_world_scaffold_test.gd
+│   ├── npc_visual_lifecycle_test.gd
 │   ├── resource_node_player_parity_test.gd
 │   ├── simulation_definitions_test.gd
 │   └── simulation_state_serialization_test.gd
@@ -515,6 +516,8 @@ These are expected prototype constraints, not necessarily isolated bugs:
   goals, or social knowledge.
 - NPC reasoning is logged but not presented through an in-game inspector.
 - 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.
 - There is no spatial query/index layer for large populations.
 - SimulationManager still orchestrates multiple systems and player-facing
   mutation APIs, but selection, execution, target resolution, and active-world
@@ -715,12 +718,8 @@ visual milestone should support or reveal actual simulation state.
 
 ## Immediate milestone: scaffold, architecture gate, then simulation garden
 
-Food and wood migration and the deliberately minimal `JajceWorld` scaffold,
-greybox, navigation spike, and stable-ID placement proof are complete. Do not
-proceed directly from that proof into open-ended beauty production.
-
-The architecture gate is now the active milestone. Its first five slices are
-complete:
+Food and wood migration, the minimal `JajceWorld` proof, and the mandatory
+architecture gate are complete:
 
 - explicit fixed-step simulation clock;
 - seeded per-NPC decision and wander random streams;
@@ -732,11 +731,14 @@ complete:
 - stable StringName action/profession IDs plus validated custom definition
   resources used by simulation, targeting, generation, and persistence;
 - separate selection, execution, target resolution, active-world query, and
-  visual travel responsibilities.
+  visual travel responsibilities;
+- authoritative active position and persisted travel destinations;
+- checksum-invariant NPC visual unload/reload with reservation preservation.
 
-The remaining gate work is:
-
-- explicit synchronization of active NPC position.
+The next systems milestone is a complete location-based food loop: storage,
+inventory, carrying, depositing, withdrawing, and eating through transactions.
+Bounded Terrain3D look-development can resume, but runtime terrain integration
+should remain coordinated with that visible systems slice.
 
 The coherent visual slice can then aim for: