test(simulation): QA coverage for Phase 2 verbs, sprint suppression, occupancy, inventory

Add comprehensive test suites across sprint 6 systems:
- Phase 2 observer filter: Confront injection, archetype label relabeling,
  contradiction marking, POI priority ordering (12 tests)
- Sprint anomaly: detection during sprint, queue semantics, delay timing,
  D-055 visible-but-suppressed integration (7 tests)
- Wire format: Confront and CharacterArchetype msgpack roundtrip (4 tests)
- TilePresence: 4-layer coexistence on same tile (1 test)
- Inventory: Take/Place full roundtrip, capacity enforcement (3 tests)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/simulation/movement.rs

@@ -857,4 +857,50 @@ mod tests {
             "two Fixtures on same tile should collide"
         );
     }
+
+    #[test]
+    fn all_four_layers_coexist_on_same_tile() {
+        // D-054: Standing + Prone + Seated + Fixture all share one tile
+        let mut world = bevy_ecs::world::World::new();
+        world.insert_resource(WalkabilityMap::new(10, 10, 1));
+
+        let target = TilePosition::new(5, 4, 0);
+
+        // Fixture and Prone already at tile
+        world.spawn((target, TilePresence::Fixture));
+        world.spawn((target, TilePresence::Prone));
+
+        // Standing mover enters
+        let standing = world
+            .spawn((
+                TilePosition::new(5, 5, 0),
+                TilePresence::Standing,
+                MoveIntent { target },
+            ))
+            .id();
+
+        // Seated mover enters from elsewhere
+        let seated = world
+            .spawn((
+                TilePosition::new(5, 3, 0),
+                TilePresence::Seated,
+                MoveIntent { target },
+            ))
+            .id();
+
+        let mut schedule = bevy_ecs::schedule::Schedule::default();
+        schedule.add_systems(validate_movement);
+        schedule.run(&mut world);
+
+        assert_eq!(
+            *world.get::<TilePosition>(standing).unwrap(),
+            target,
+            "Standing should share tile with Fixture + Prone"
+        );
+        assert_eq!(
+            *world.get::<TilePosition>(seated).unwrap(),
+            target,
+            "Seated should share tile with Fixture + Prone + Standing"
+        );
+    }
 }