diff --git a/src/simulator/api-gdext/src/lib.rs b/src/simulator/api-gdext/src/lib.rs
index 0d75d937..28e8c877 100644
--- a/src/simulator/api-gdext/src/lib.rs
+++ b/src/simulator/api-gdext/src/lib.rs
@@ -965,6 +965,34 @@ impl GdClimateSpecEval {
     }
 }
 
+// ── BuildingEntity Dictionary conversion helper ─────────────────────────
+//
+// Shape mirrors `Building.gd::to_dict()` exactly — same key set, same
+// value types, same `position: [col, row]` array — so renderers and
+// encyclopedia panels can keep consuming the dict shape during the
+// Stage 2b → Stage 3 transition. The inverse path (Dictionary →
+// BuildingEntity) is not needed today; spawn callers pass the field
+// set positionally to `GdGameState::spawn_npc_building`.
+
+fn building_entity_to_dict(entity: &mc_core::BuildingEntity) -> Dictionary {
+    let mut d: Dictionary = Dictionary::new();
+    d.set("id", GString::from(entity.id.as_str()));
+    d.set("type_id", GString::from(entity.type_id.as_str()));
+    d.set("name", GString::from(entity.name.as_str()));
+    let placement_str = match entity.placement {
+        mc_core::Placement::Map => "map",
+        mc_core::Placement::City => "city",
+    };
+    d.set("placement", GString::from(placement_str));
+    d.set("owner", entity.owner as i64);
+    let mut position = Array::<i64>::new();
+    position.push(entity.position.0 as i64);
+    position.push(entity.position.1 as i64);
+    d.set("position", position);
+    d.set("visited", entity.visited);
+    d
+}
+
 // ── Tile Dictionary conversion helpers ──────────────────────────────────
 
 fn tile_to_dict(tile: &mc_core::grid::TileState) -> Dictionary {
@@ -2981,6 +3009,159 @@ impl GdGameState {
         true
     }
 
+    // ── p2-72a Stage 2b: NPC-buildings accessor surface ─────────────────
+    //
+    // Stage 2b makes the Rust-side `npc_buildings: Vec<BuildingEntity>`
+    // mirror of `GameState.npc_buildings` (GDScript) authoritative for
+    // save-format purposes. The full read-path migration (renderer / AI
+    // / encyclopedia / fauna) lands in Stage 3+ — for now GDScript
+    // continues to maintain its own `BuildingScript` array as a view
+    // alongside the Rust mirror, and every spawn / mutate / remove path
+    // routes through these accessors so the mirror stays in lockstep.
+
+    /// Number of NPC buildings currently in the Rust mirror.
+    #[func]
+    fn npc_building_count(&self) -> i64 {
+        self.inner.npc_buildings.len() as i64
+    }
+
+    /// Return the building at `idx` as a `Dictionary` shaped to match
+    /// `Building.gd::to_dict()`. Returns an empty `Dictionary` if `idx`
+    /// is out of range (logged via `godot_error!`). Renderers and
+    /// encyclopedia panels consume this shape today.
+    #[func]
+    fn npc_building_dict(&self, idx: i64) -> Dictionary {
+        if idx < 0 || (idx as usize) >= self.inner.npc_buildings.len() {
+            godot_error!(
+                "GdGameState::npc_building_dict: idx {idx} out of range (len {})",
+                self.inner.npc_buildings.len()
+            );
+            return Dictionary::new();
+        }
+        building_entity_to_dict(&self.inner.npc_buildings[idx as usize])
+    }
+
+    /// Return every NPC building as an `Array<Dictionary>` (one entry
+    /// per building, ordered by insertion). Used by Stage 3 read-path
+    /// migration to drain the Rust mirror into renderer/encyclopedia
+    /// data structures.
+    #[func]
+    fn npc_buildings_all(&self) -> Array<Dictionary> {
+        let mut arr = Array::new();
+        for b in &self.inner.npc_buildings {
+            arr.push(&building_entity_to_dict(b));
+        }
+        arr
+    }
+
+    /// Append a new NPC building to the Rust mirror. Called by every
+    /// GDScript spawn path (`VillageLairPlacer._create_npc_building`)
+    /// in lieu of allocating a `BuildingScript` and appending it to
+    /// `GameState.npc_buildings` directly. Returns the index of the
+    /// newly inserted entity.
+    ///
+    /// Parameters mirror `BuildingEntity` field-for-field; `placement`
+    /// accepts the GDScript-shaped lowercase strings `"map"` /
+    /// `"city"` and falls back to `"map"` on any other value (with a
+    /// `godot_error!`).
+    #[func]
+    fn spawn_npc_building(
+        &mut self,
+        id: GString,
+        type_id: GString,
+        name: GString,
+        placement: GString,
+        owner: i64,
+        col: i64,
+        row: i64,
+        visited: bool,
+    ) -> i64 {
+        let placement = match placement.to_string().as_str() {
+            "map" => mc_core::Placement::Map,
+            "city" => mc_core::Placement::City,
+            other => {
+                godot_error!(
+                    "GdGameState::spawn_npc_building: unknown placement '{other}', defaulting to 'map'"
+                );
+                mc_core::Placement::Map
+            }
+        };
+        let entity = mc_core::BuildingEntity {
+            id: id.to_string(),
+            type_id: type_id.to_string(),
+            name: name.to_string(),
+            placement,
+            owner: owner as i32,
+            position: (col as i32, row as i32),
+            visited,
+        };
+        let idx = self.inner.npc_buildings.len() as i64;
+        self.inner.npc_buildings.push(entity);
+        idx
+    }
+
+    /// Drop an NPC building from the mirror by instance id. Returns
+    /// `true` if a matching entity was removed. Used by Stage 3+
+    /// remove-paths (raid-clear, lair-destroyed). Linear scan because
+    /// `Vec<BuildingEntity>` keeps the on-disk save shape simple — the
+    /// spatial-index migration that would replace this with a
+    /// `BTreeMap<AxialPos, Vec<usize>>` is Stage 3 scope.
+    #[func]
+    fn remove_npc_building_by_id(&mut self, id: GString) -> bool {
+        let target = id.to_string();
+        if let Some(pos) = self.inner.npc_buildings.iter().position(|b| b.id == target) {
+            self.inner.npc_buildings.remove(pos);
+            true
+        } else {
+            false
+        }
+    }
+
+    /// Mark an NPC building as visited / unvisited by instance id.
+    /// Returns `true` if a matching entity was found and updated.
+    #[func]
+    fn set_npc_building_visited(&mut self, id: GString, visited: bool) -> bool {
+        let target = id.to_string();
+        if let Some(b) = self.inner.npc_buildings.iter_mut().find(|b| b.id == target) {
+            b.visited = visited;
+            true
+        } else {
+            false
+        }
+    }
+
+    /// Convert an NPC building's `type_id` (and `name`) in-place by
+    /// instance id. Used by the lair-abandonment / ruin-conversion
+    /// paths in `ecological_event_handlers_b.gd::_abandon_lair` and
+    /// `fauna.gd::_abandon_lair`, which today mutate the GDScript
+    /// `BuildingScript` instance directly. The Rust mirror tracks the
+    /// same mutation so the save round-trip emits the post-conversion
+    /// state. Returns `true` if a matching entity was found.
+    #[func]
+    fn convert_npc_building_type(
+        &mut self,
+        id: GString,
+        new_type_id: GString,
+        new_name: GString,
+    ) -> bool {
+        let target = id.to_string();
+        if let Some(b) = self.inner.npc_buildings.iter_mut().find(|b| b.id == target) {
+            b.type_id = new_type_id.to_string();
+            b.name = new_name.to_string();
+            true
+        } else {
+            false
+        }
+    }
+
+    /// Reset the NPC-buildings mirror to empty. Called by
+    /// `GameState.initialize_game` to clear stale entities between
+    /// games / save loads before fresh spawn paths run.
+    #[func]
+    fn clear_npc_buildings(&mut self) {
+        self.inner.npc_buildings.clear();
+    }
+
     /// p2-71c — load the runtime `UnitsCatalog` (id → `UnitStats`) from a
     /// JSON array harvested from `public/resources/units/*.json`. GDScript
     /// reads every per-unit file, collects them into an `Array`, and