feat(@projects/@magic-civilization): ✨ add per-tile fauna density updates

Co-Authored-By: Lilith Autocommit <noreply@atlilith.com>

src/game/engine/src/autoloads/ecology_state.gd

@@ -46,6 +46,17 @@ func tick(grid: RefCounted, seed: int) -> void:
 	fauna_ecology.call("tick_populations", grid, seed)
 
 
+## Per-tile total fauna population for the live-map fauna overlay
+## (`fauna_overlay_renderer.gd`). One bulk bridge read per refresh: a Dictionary
+## keyed by `Vector2i(col, row)` → total population (float). Empty when no
+## engine or no populations yet (emergence has not fired). The overlay reads
+## this on each `EventBus.worldsim_updated` and normalizes for its heatmap.
+func tile_densities() -> Dictionary:
+	if fauna_ecology == null:
+		return {}
+	return fauna_ecology.call("populated_tile_densities")
+
+
 func _ensure_species_registered() -> void:
 	## Idempotent: a non-empty registry short-circuits via the engine's
 	## `population_slot_count` proxy on subsequent ticks (slots only appear

src/game/engine/src/autoloads/event_bus.gd

@@ -272,6 +272,11 @@ signal creature_died(pos: Vector2i, species_name: String, quality: int)
 signal creature_born(pos: Vector2i, species_name: String)
 ## Tile crossed Q4 threshold — natural wonder emerged from ecology.
 signal landmark_formed(pos: Vector2i, name: String, quality: int)
+## Emitted once per full game turn after the continuous worldsim has advanced
+## (climate physics + fauna `EcologyState.tick` + `WorldsimState.dispatch`).
+## The fauna overlay subscribes to refresh its per-tile density heatmap so the
+## evolving living world is visible on the playable map (p2-80 render hook).
+signal worldsim_updated(turn: int)
 
 # -- Natural event signals --
 signal natural_event_spawned(event_type: String, position: Vector2i, intensity: float)

src/game/engine/src/autoloads/turn_manager.gd

@@ -301,6 +301,10 @@ func next_player() -> void:
 					WorldsimState.dispatch(
 						fauna_grid, GameState.turn_number, GameState.map_seed
 					)
+					# p2-80 render hook: signal the fauna overlay to refresh its
+					# per-tile density heatmap so the evolving living world is
+					# visible on the playable map, not just simulated.
+					EventBus.worldsim_updated.emit(GameState.turn_number)
 		GameState.current_player_index = 0
 		GameState.turn_number += 1
 		# Check victory conditions after all players have moved

src/simulator/api-gdext/src/lib.rs

@@ -851,6 +851,26 @@ impl GdFaunaEcology {
     fn populated_tile_count(&self) -> i64 {
         self.inner.tile_populations.len() as i64
     }
+
+    /// Per-tile total fauna population, as a `Dictionary` keyed by
+    /// `Vector2i(col, row)` → total population (`f64`, summed across all species
+    /// slots on the tile). One bulk read so the live-map fauna overlay
+    /// (`fauna_overlay_renderer.gd`) refreshes per turn with a single bridge
+    /// call instead of `populated_tile_count`×`populations_on_tile`. Tiles with
+    /// zero population are omitted (the map is sparse, mirroring the engine's
+    /// own `tile_populations`). Deterministic order is irrelevant here — the
+    /// renderer keys by position, not iteration order.
+    #[func]
+    fn populated_tile_densities(&self) -> Dictionary {
+        let mut out = Dictionary::new();
+        for (&(col, row), slots) in &self.inner.tile_populations {
+            let total: f32 = slots.iter().map(|s| s.population).sum();
+            if total > 0.0 {
+                out.set(Vector2i::new(col, row), f64::from(total));
+            }
+        }
+        out
+    }
 }
 
 // ── GdAtmosphericChemistry ──────────────────────────────────────────────