feat(core): items & creatures — entity layer + EntityPlacer (9th pass)

The roadmap capstone: the dungeon is now populated.

- New entity layer: src/entity.rs (Entity { kind, at }, EntityKind {Entrance,
  Exit, Treasure, Monster}); Map gains an `entities: Vec<Entity>` overlay field
  (serde round-tripped). Entities aren't terrain, so no new Tile and the frozen
  viz is untouched.
- EntityPlacer/EntityConfig: places one Entrance (random room), one Exit (the
  room farthest from it — a traversal goal), per-room Treasure (treasure_chance)
  and Monsters (monster_chance, 1..=max, never in the entrance room). All on
  plain Floor only, never two per cell, fully deterministic.
- Handoff via the Blackboard (the designed side channel for non-tile/region/edge
  data) under entity::BLACKBOARD_KEY, harvested by Pipeline into Map.entities —
  so GenContext's 25 literals stay untouched.
- Renderer draws iconic markers on the final stage: green beacon (entrance),
  cyan portal (exit), gold diamond (treasure), crimson eyed-blob (monster), each
  with a soft glow. New entities toggle + treasure/monster sliders + readout.

Core: 135 tests green (6 new: one entrance/one exit on distinct floor, entrance
room monster-free, determinism, empty-map, recipe populated-check). clippy
clean. Pipeline is now 9 passes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

reikhelm-core/src/ascii.rs

@@ -85,6 +85,7 @@ mod tests {
             tiles,
             regions: Vec::new(),
             graph: ConnGraph::new(),
+            entities: Vec::new(),
             seed: 0,
             width: 3,
             height: 3,

reikhelm-core/src/entity.rs

@@ -0,0 +1,57 @@
+//! Entities: the things that *populate* a map, distinct from its terrain.
+//!
+//! Where [`Tile`](crate::map::Tile) says *what the ground is* and
+//! [`Region`](crate::region::Region) says *what areas exist*, an [`Entity`] is a
+//! discrete thing sitting **on** a walkable cell — a stairway, a chest, a
+//! monster. Entities never change the terrain (they are an overlay layer on the
+//! [`Map`](crate::map::Map)), so a renderer draws them on top of the tiles and a
+//! game treats them as occupants of a cell.
+//!
+//! Like [`Tile`](crate::map::Tile) and [`RegionKind`](crate::region::RegionKind),
+//! the kind enum starts minimal and grows additively; passes and renderers match
+//! only on the kinds they care about. All types derive serde so entities travel
+//! inside a `Map` through JSON.
+
+use serde::{Deserialize, Serialize};
+
+use crate::geometry::Point;
+
+/// The [`Blackboard`](crate::blackboard::Blackboard) key under which the entity
+/// placer stashes its `Vec<Entity>` for [`Pipeline`](crate::pass::Pipeline) to
+/// harvest into the finished [`Map`](crate::map::Map). Shared so the producer
+/// (the placer pass) and the consumer (the engine) never drift on the name.
+pub const BLACKBOARD_KEY: &str = "entities";
+
+/// What an [`Entity`] is. Additive: new kinds (traps, NPCs, altars, …) slot in
+/// without disturbing existing matches.
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+pub enum EntityKind {
+    /// Where the dungeon is entered from (the player's start / stairs up).
+    Entrance,
+    /// The dungeon's goal — the room farthest from the entrance (stairs down).
+    Exit,
+    /// A pickup: treasure, loot, an item.
+    Treasure,
+    /// A creature occupying the cell.
+    Monster,
+}
+
+/// A single entity: its [`EntityKind`] and the cell it occupies.
+///
+/// `at` is always a walkable [`Floor`](crate::map::Tile::Floor) cell in a
+/// well-formed map; the placer only ever drops entities onto open floor and never
+/// stacks two on one cell.
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, Serialize, Deserialize)]
+pub struct Entity {
+    /// What this entity is.
+    pub kind: EntityKind,
+    /// The cell it occupies.
+    pub at: Point,
+}
+
+impl Entity {
+    /// Creates an entity of `kind` at cell `at`.
+    pub const fn new(kind: EntityKind, at: Point) -> Self {
+        Entity { kind, at }
+    }
+}

reikhelm-core/src/lib.rs

@@ -5,6 +5,7 @@
 
 pub mod ascii;
 pub mod blackboard;
+pub mod entity;
 pub mod geometry;
 pub mod grid;
 pub mod map;

reikhelm-core/src/map.rs

@@ -11,6 +11,7 @@
 
 use serde::{Deserialize, Serialize};
 
+use crate::entity::Entity;
 use crate::grid::Grid;
 use crate::region::{ConnGraph, Region};
 
@@ -59,6 +60,9 @@ pub struct Map {
     pub regions: Vec<Region>,
     /// How regions connect (each edge is a door/corridor link).
     pub graph: ConnGraph,
+    /// The entities populating the map (entrance, exit, treasure, monsters) —
+    /// an overlay on the terrain, each sitting on a walkable cell.
+    pub entities: Vec<Entity>,
     /// The seed that produced this map, for reproducibility.
     pub seed: u64,
     /// Map width in cells.
@@ -70,6 +74,7 @@ pub struct Map {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::entity::{Entity, EntityKind};
     use crate::geometry::{Point, Rect};
     use crate::region::{RegionId, RegionKind};
 
@@ -94,6 +99,7 @@ mod tests {
             tiles,
             regions: vec![region],
             graph,
+            entities: vec![Entity::new(EntityKind::Treasure, Point::new(1, 0))],
             seed: 0xDEAD_BEEF,
             width: 3,
             height: 2,
@@ -116,6 +122,7 @@ mod tests {
         // Spot-check the semantic layer, which does implement `Eq`, directly.
         assert_eq!(original.regions, restored.regions);
         assert_eq!(original.graph, restored.graph);
+        assert_eq!(original.entities, restored.entities);
         assert_eq!(original.seed, restored.seed);
         assert_eq!(
             (original.width, original.height),

reikhelm-core/src/pass.rs

@@ -34,6 +34,7 @@
 //! resulting [`Map`] is identical for a given seed with or without snapshots.
 
 use crate::blackboard::Blackboard;
+use crate::entity::Entity;
 use crate::geometry::{Point, Rect};
 use crate::grid::Grid;
 use crate::map::{Map, Tile};
@@ -231,10 +232,18 @@ impl Pipeline {
             }
         }
 
+        // Harvest the entity layer the placer (if any) stashed on the blackboard
+        // — the side channel for data that isn't a tile/region/edge (§4.6). A
+        // recipe with no placer simply yields no entities.
+        let entities = ctx
+            .blackboard
+            .take::<Vec<Entity>>(crate::entity::BLACKBOARD_KEY)
+            .unwrap_or_default();
         let map = Map {
             tiles: ctx.tiles,
             regions: ctx.regions,
             graph: ctx.graph,
+            entities,
             seed,
             width: self.width,
             height: self.height,

reikhelm-core/src/passes/entity_placer.rs

@@ -0,0 +1,277 @@
+//! The [`EntityPlacer`] pass: populate the dungeon with entities.
+//!
+//! A *placer* that drops [`Entity`](crate::entity::Entity)s onto open floor — the
+//! final pass of the dungeon recipe, after all terrain (rooms, caves, corridors,
+//! doors, pools, pillars) is settled. It changes **no** tiles or regions; it
+//! produces an overlay layer the engine harvests into [`Map::entities`](crate::map::Map::entities).
+//!
+//! Because [`GenContext`] has no entity field (entities aren't tiles, regions, or
+//! edges), this pass stashes its `Vec<Entity>` on the [`Blackboard`](crate::blackboard::Blackboard)
+//! under [`crate::entity::BLACKBOARD_KEY`] — the side channel designed for exactly
+//! this kind of cross-pass/-engine handoff (spec §4.6) — and
+//! [`Pipeline`](crate::pass::Pipeline) takes it out into the final `Map`.
+//!
+//! Placement, in a fixed (deterministic) order:
+//!
+//! 1. **Entrance** — a random room; the entity sits on the floor cell nearest its
+//!    center.
+//! 2. **Exit** — the room whose center is farthest (Manhattan) from the entrance,
+//!    again on its central floor cell. Gives the dungeon a traversal goal.
+//! 3. **Treasure** — each room has a `treasure_chance` of holding one, on a random
+//!    open floor cell.
+//! 4. **Monsters** — each room *except the entrance room* has a `monster_chance` of
+//!    holding 1..=`max_monsters`, scattered on open floor.
+//!
+//! Entities only ever land on plain [`Floor`](crate::map::Tile::Floor) (never a
+//! door, pool, pillar, or wall), and never two on one cell, so a renderer or game
+//! can treat `at` as a free walkable cell.
+
+use serde::{Deserialize, Serialize};
+use std::collections::BTreeSet;
+
+use crate::entity::{Entity, EntityKind, BLACKBOARD_KEY};
+use crate::geometry::Point;
+use crate::map::Tile;
+use crate::pass::{GenContext, Pass};
+use crate::region::{Region, RegionKind};
+use crate::rng::Rng;
+
+/// Configuration for an [`EntityPlacer`] pass.
+#[derive(Clone, Copy, Debug, PartialEq, Serialize, Deserialize)]
+pub struct EntityConfig {
+    /// Probability that a given room holds a treasure.
+    pub treasure_chance: f64,
+    /// Probability that a given room (other than the entrance room) holds
+    /// monsters.
+    pub monster_chance: f64,
+    /// The most monsters a single monster-room may hold (each placed on its own
+    /// floor cell). The actual count is `1..=max_monsters`.
+    pub max_monsters: i32,
+}
+
+impl Default for EntityConfig {
+    /// A sensible default: about a third of rooms hold treasure, half hold up to
+    /// three monsters.
+    fn default() -> Self {
+        EntityConfig {
+            treasure_chance: 0.35,
+            monster_chance: 0.50,
+            max_monsters: 3,
+        }
+    }
+}
+
+/// An entity-placing pass.
+///
+/// Construct one with [`EntityPlacer::new`]; it implements [`Pass`] with the
+/// stable name `"entity_placer"`.
+#[derive(Clone, Copy, Debug, PartialEq)]
+pub struct EntityPlacer {
+    cfg: EntityConfig,
+}
+
+impl EntityPlacer {
+    /// Creates an entity placer with the given configuration.
+    pub fn new(cfg: EntityConfig) -> Self {
+        EntityPlacer { cfg }
+    }
+}
+
+/// A real room's data, snapshotted so placement doesn't hold a borrow on `ctx`.
+struct RoomInfo {
+    center: Point,
+    /// The room's open-floor cells (Tile::Floor only), row-major.
+    floor: Vec<Point>,
+}
+
+impl Pass for EntityPlacer {
+    fn name(&self) -> &str {
+        "entity_placer"
+    }
+
+    fn apply(&self, ctx: &mut GenContext, rng: &mut Rng) {
+        // Snapshot each real room's center and its open-floor cells. Only plain
+        // Floor counts — doors, pools, pillars and walls are never entity homes.
+        let rooms: Vec<RoomInfo> = ctx
+            .regions
+            .iter()
+            .filter(|r: &&Region| r.kind == RegionKind::Room && !r.cells.is_empty())
+            .map(|r| RoomInfo {
+                center: r.bounds.center(),
+                floor: r
+                    .cells
+                    .iter()
+                    .copied()
+                    .filter(|&p| ctx.tiles.get(p) == Some(&Tile::Floor))
+                    .collect(),
+            })
+            .collect();
+
+        let mut entities: Vec<Entity> = Vec::new();
+        let mut taken: BTreeSet<(i32, i32)> = BTreeSet::new();
+
+        if !rooms.is_empty() {
+            // 1) Entrance — a random room, central floor cell.
+            let entrance_idx = rng.range(0, rooms.len() as i32) as usize;
+            if let Some(p) = nearest_free(&rooms[entrance_idx], rooms[entrance_idx].center, &taken) {
+                taken.insert((p.x, p.y));
+                entities.push(Entity::new(EntityKind::Entrance, p));
+            }
+
+            // 2) Exit — the room whose center is farthest from the entrance.
+            let from = rooms[entrance_idx].center;
+            let exit_idx = (0..rooms.len())
+                .max_by_key(|&i| rooms[i].center.manhattan(from))
+                .unwrap_or(entrance_idx);
+            if let Some(p) = nearest_free(&rooms[exit_idx], rooms[exit_idx].center, &taken) {
+                taken.insert((p.x, p.y));
+                entities.push(Entity::new(EntityKind::Exit, p));
+            }
+
+            // 3 & 4) Per-room treasure and monsters, in room order for determinism.
+            for (i, room) in rooms.iter().enumerate() {
+                if rng.chance(self.cfg.treasure_chance) {
+                    if let Some(p) = choose_free(room, &taken, rng) {
+                        taken.insert((p.x, p.y));
+                        entities.push(Entity::new(EntityKind::Treasure, p));
+                    }
+                }
+                // Keep the entrance room clear of monsters.
+                if i != entrance_idx && rng.chance(self.cfg.monster_chance) {
+                    let n = rng.range(1, self.cfg.max_monsters.max(1) + 1);
+                    for _ in 0..n {
+                        match choose_free(room, &taken, rng) {
+                            Some(p) => {
+                                taken.insert((p.x, p.y));
+                                entities.push(Entity::new(EntityKind::Monster, p));
+                            }
+                            None => break, // room is full
+                        }
+                    }
+                }
+            }
+        }
+
+        ctx.blackboard.insert(BLACKBOARD_KEY, entities);
+    }
+}
+
+/// The room's free floor cell nearest `target`, or [`None`] if none are free.
+fn nearest_free(room: &RoomInfo, target: Point, taken: &BTreeSet<(i32, i32)>) -> Option<Point> {
+    room.floor
+        .iter()
+        .copied()
+        .filter(|p| !taken.contains(&(p.x, p.y)))
+        .min_by_key(|p| (p.x - target.x).pow(2) + (p.y - target.y).pow(2))
+}
+
+/// A uniformly random free floor cell of the room, drawn from `rng`, or [`None`].
+fn choose_free(room: &RoomInfo, taken: &BTreeSet<(i32, i32)>, rng: &mut Rng) -> Option<Point> {
+    let free: Vec<Point> = room
+        .floor
+        .iter()
+        .copied()
+        .filter(|p| !taken.contains(&(p.x, p.y)))
+        .collect();
+    rng.choose(&free).copied()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::blackboard::Blackboard;
+    use crate::geometry::Rect;
+    use crate::grid::Grid;
+    use crate::region::{ConnGraph, RegionId};
+
+    /// Builds a context with `rooms` rectangular Floor rooms (each `(x,y,w,h)`).
+    fn ctx_with_rooms(w: u32, h: u32, rooms: &[(i32, i32, i32, i32)]) -> GenContext {
+        let mut ctx = GenContext {
+            tiles: Grid::new(w, h, Tile::Wall),
+            regions: Vec::new(),
+            graph: ConnGraph::new(),
+            blackboard: Blackboard::new(),
+        };
+        for &(x, y, rw, rh) in rooms {
+            let bounds = Rect::new(x, y, rw, rh);
+            let cells: Vec<Point> = bounds.iter().collect();
+            for &p in &cells {
+                ctx.tiles.set(p, Tile::Floor);
+            }
+            ctx.add_region(RegionKind::Room, bounds, cells);
+        }
+        ctx
+    }
+
+    fn run(ctx: &mut GenContext, cfg: EntityConfig, seed: u64) -> Vec<Entity> {
+        let mut rng = Rng::from_seed(seed).fork("entity_placer#0");
+        EntityPlacer::new(cfg).apply(ctx, &mut rng);
+        ctx.blackboard.take::<Vec<Entity>>(BLACKBOARD_KEY).unwrap_or_default()
+    }
+
+    #[test]
+    fn name_is_entity_placer() {
+        assert_eq!(EntityPlacer::new(EntityConfig::default()).name(), "entity_placer");
+    }
+
+    /// A multi-room map gets exactly one entrance and one exit, on distinct floor
+    /// cells, and every entity sits on a Floor cell with no two sharing a cell.
+    #[test]
+    fn places_one_entrance_one_exit_on_distinct_floor() {
+        let rooms = [(0, 0, 8, 8), (20, 0, 8, 8), (0, 12, 8, 8)];
+        let mut ctx = ctx_with_rooms(32, 24, &rooms);
+        let entities = run(&mut ctx, EntityConfig::default(), 0x1234);
+
+        let entrances = entities.iter().filter(|e| e.kind == EntityKind::Entrance).count();
+        let exits = entities.iter().filter(|e| e.kind == EntityKind::Exit).count();
+        assert_eq!(entrances, 1, "exactly one entrance");
+        assert_eq!(exits, 1, "exactly one exit");
+
+        // Every entity on Floor; all on distinct cells.
+        let mut cells = BTreeSet::new();
+        for e in &entities {
+            assert_eq!(ctx.tiles.get(e.at), Some(&Tile::Floor), "entity {e:?} not on Floor");
+            assert!(cells.insert((e.at.x, e.at.y)), "two entities share cell {:?}", e.at);
+        }
+
+        // Entrance and exit are different cells (different rooms here).
+        let entrance = entities.iter().find(|e| e.kind == EntityKind::Entrance).unwrap();
+        let exit = entities.iter().find(|e| e.kind == EntityKind::Exit).unwrap();
+        assert_ne!(entrance.at, exit.at);
+    }
+
+    /// No monster shares the entrance room; the entrance room is a safe start.
+    #[test]
+    fn entrance_room_has_no_monsters() {
+        let rooms = [(0, 0, 8, 8), (20, 0, 8, 8), (0, 12, 8, 8)];
+        let mut ctx = ctx_with_rooms(32, 24, &rooms);
+        // Force monsters everywhere they're allowed.
+        let cfg = EntityConfig { treasure_chance: 0.0, monster_chance: 1.0, max_monsters: 3 };
+        let entities = run(&mut ctx, cfg, 7);
+
+        let entrance = entities.iter().find(|e| e.kind == EntityKind::Entrance).unwrap().at;
+        // Which room contains the entrance?
+        let in_room = |p: Point, r: (i32, i32, i32, i32)| Rect::new(r.0, r.1, r.2, r.3).contains(p);
+        let entrance_room = rooms.iter().copied().find(|&r| in_room(entrance, r)).unwrap();
+        for m in entities.iter().filter(|e| e.kind == EntityKind::Monster) {
+            assert!(!in_room(m.at, entrance_room), "monster {m:?} spawned in the entrance room");
+        }
+    }
+
+    /// Same seed reproduces the exact same entity layer.
+    #[test]
+    fn placement_is_deterministic() {
+        let rooms = [(0, 0, 8, 8), (20, 0, 8, 8), (0, 12, 8, 8), (20, 12, 8, 8)];
+        let cfg = EntityConfig::default();
+        let mut a = ctx_with_rooms(32, 24, &rooms);
+        let mut b = ctx_with_rooms(32, 24, &rooms);
+        assert_eq!(run(&mut a, cfg, 0x5EED), run(&mut b, cfg, 0x5EED));
+    }
+
+    /// An empty map (no rooms) places no entities and does not panic.
+    #[test]
+    fn no_rooms_places_nothing() {
+        let mut ctx = ctx_with_rooms(8, 8, &[]);
+        assert!(run(&mut ctx, EntityConfig::default(), 1).is_empty());
+    }
+}

reikhelm-core/src/passes/mod.rs

@@ -46,3 +46,6 @@ pub use pool::{PoolConfig, PoolDecorator};
 
 pub mod pillar;
 pub use pillar::{PillarConfig, PillarPlacer};
+
+pub mod entity_placer;
+pub use entity_placer::{EntityConfig, EntityPlacer};

reikhelm-core/src/recipes/dungeon.rs

@@ -7,7 +7,7 @@
 //!
 //! ```text
 //! BspPartition → RoomCarver → CaveShaper → MstConnect → CorridorCarver
-//!   → DoorPlacer → PoolDecorator → PillarPlacer
+//!   → DoorPlacer → PoolDecorator → PillarPlacer → EntityPlacer
 //! ```
 //!
 //! 1. [`BspPartition`] cuts the canvas into leaf rectangles (one placeholder
@@ -24,6 +24,8 @@
 //!    (a connectivity-guarded decorator — never orphans part of a room).
 //! 7. [`PillarPlacer`] scatters free-standing pillars into larger rooms (a
 //!    finishing decorator; isolated obstacles that never break connectivity).
+//! 8. [`EntityPlacer`] populates the dungeon — an entrance, a far-off exit, and
+//!    scattered treasure and monsters — as an overlay layer (no terrain change).
 //!
 //! ## Why validation matters (spec §8)
 //!
@@ -46,8 +48,8 @@ use serde::{Deserialize, Serialize};
 use crate::pass::Pipeline;
 use crate::passes::{
     BspConfig, BspPartition, CaveConfig, CaveShaper, ConnectConfig, CorridorCarver, DoorConfig,
-    DoorPlacer, MstConnect, PillarConfig, PillarPlacer, PoolConfig, PoolDecorator, RoomCarver,
-    RoomConfig, ShapeWeights,
+    DoorPlacer, EntityConfig, EntityPlacer, MstConnect, PillarConfig, PillarPlacer, PoolConfig,
+    PoolDecorator, RoomCarver, RoomConfig, ShapeWeights,
 };
 
 /// Configuration for the [`dungeon`] recipe.
@@ -76,6 +78,9 @@ pub struct DungeonConfig {
     pub pools: PoolConfig,
     /// How free-standing pillars are scattered into larger rooms (decorator).
     pub pillars: PillarConfig,
+    /// How the dungeon is populated with entities (entrance, exit, treasure,
+    /// monsters).
+    pub entities: EntityConfig,
 }
 
 impl Default for DungeonConfig {
@@ -113,6 +118,7 @@ impl Default for DungeonConfig {
             doors: DoorConfig::default(),
             pools: PoolConfig::default(),
             pillars: PillarConfig::default(),
+            entities: EntityConfig::default(),
         }
     }
 }
@@ -226,7 +232,8 @@ pub fn dungeon(cfg: DungeonConfig) -> Result<Pipeline, ConfigError> {
         .then(CorridorCarver::new())
         .then(DoorPlacer::new(cfg.doors))
         .then(PoolDecorator::new(cfg.pools))
-        .then(PillarPlacer::new(cfg.pillars));
+        .then(PillarPlacer::new(cfg.pillars))
+        .then(EntityPlacer::new(cfg.entities));
 
     Ok(pipeline)
 }
@@ -240,7 +247,7 @@ mod tests {
     use std::collections::{BTreeSet, VecDeque};
 
     /// The pass names in pipeline order, used to check snapshot labels.
-    const PASS_NAMES: [&str; 8] = [
+    const PASS_NAMES: [&str; 9] = [
         "bsp_partition",
         "room_carver",
         "cave_shaper",
@@ -249,6 +256,7 @@ mod tests {
         "door_placer",
         "pool_decorator",
         "pillar_placer",
+        "entity_placer",
     ];
 
     /// Is `p` a walkable cell (Floor or Door are both walkable; Wall is not)?
@@ -314,7 +322,7 @@ mod tests {
         let (snapped, snapshots) = dungeon(cfg).unwrap().run_with_snapshots(7);
 
         assert_eq!(plain, snapped, "snapshotting must not change the map");
-        assert_eq!(snapshots.len(), 8, "one snapshot per pass (eight passes)");
+        assert_eq!(snapshots.len(), 9, "one snapshot per pass (nine passes)");
 
         let labels: Vec<&str> = snapshots.iter().map(|s| s.label.as_str()).collect();
         assert_eq!(
@@ -606,7 +614,32 @@ mod tests {
         assert!(total_full > 0, "door_chance=1.0 must place doors");
     }
 
-    // --- Test 7: eyeball render ---------------------------------------------
+    // --- Test 7: entities ---------------------------------------------------
+
+    /// The populated default dungeon has exactly one entrance and one exit across
+    /// many seeds, and every entity sits on a walkable Floor cell (never a wall,
+    /// door, pool, or pillar).
+    #[test]
+    fn default_dungeon_is_populated_with_entities() {
+        use crate::entity::EntityKind;
+        let cfg = DungeonConfig::default();
+        for seed in 1..=16u64 {
+            let map = dungeon(cfg).unwrap().run(seed);
+            let entrances = map.entities.iter().filter(|e| e.kind == EntityKind::Entrance).count();
+            let exits = map.entities.iter().filter(|e| e.kind == EntityKind::Exit).count();
+            assert_eq!(entrances, 1, "seed {seed}: expected exactly one entrance");
+            assert_eq!(exits, 1, "seed {seed}: expected exactly one exit");
+            for e in &map.entities {
+                assert_eq!(
+                    map.tiles.get(e.at),
+                    Some(&Tile::Floor),
+                    "seed {seed}: entity {e:?} must sit on Floor"
+                );
+            }
+        }
+    }
+
+    // --- Test 8: eyeball render ---------------------------------------------
 
     /// Prints one dungeon for eyeball confirmation under `--nocapture`. Not an
     /// assertion (beyond non-empty output); it documents what the recipe makes.

reikhelm-wasm/src/lib.rs

@@ -23,6 +23,7 @@
 use serde::Serialize;
 use wasm_bindgen::prelude::*;
 
+use reikhelm_core::entity::{Entity, EntityKind};
 use reikhelm_core::geometry::Point;
 use reikhelm_core::grid::Grid;
 use reikhelm_core::map::{Map, Tile};
@@ -97,6 +98,32 @@ impl From<&Region> for RegionDto {
     }
 }
 
+/// The entity-kind tag sent on the wire.
+fn entity_kind_str(kind: EntityKind) -> &'static str {
+    match kind {
+        EntityKind::Entrance => "Entrance",
+        EntityKind::Exit => "Exit",
+        EntityKind::Treasure => "Treasure",
+        EntityKind::Monster => "Monster",
+    }
+}
+
+/// An entity on the wire: its kind tag and the `[x, y]` cell it occupies.
+#[derive(Serialize)]
+struct EntityDto {
+    kind: &'static str,
+    at: [i32; 2],
+}
+
+impl From<&Entity> for EntityDto {
+    fn from(e: &Entity) -> Self {
+        EntityDto {
+            kind: entity_kind_str(e.kind),
+            at: [e.at.x, e.at.y],
+        }
+    }
+}
+
 /// A connectivity edge on the wire. `at` is the door cell once known.
 #[derive(Serialize)]
 struct EdgeDto {
@@ -145,6 +172,7 @@ struct Envelope {
     tiles: Vec<Vec<u8>>,
     regions: Vec<RegionDto>,
     edges: Vec<EdgeDto>,
+    entities: Vec<EntityDto>,
     snapshots: Vec<SnapshotDto>,
 }
 
@@ -175,6 +203,7 @@ fn build_envelope(seed: u64, map: &Map, snapshots: &[Snapshot]) -> Envelope {
         tiles: tiles_to_rows(&map.tiles),
         regions: map.regions.iter().map(RegionDto::from).collect(),
         edges: map.graph.edges().iter().map(EdgeDto::from).collect(),
+        entities: map.entities.iter().map(EntityDto::from).collect(),
         snapshots: snapshots.iter().map(SnapshotDto::from).collect(),
     }
 }

reikhelm-web/main.js

@@ -21,7 +21,7 @@ const state = {
   env: null,       // last successful envelope
   stage: 0,        // snapshot index currently shown
   followFinal: true,
-  opts: { lighting: true, outlines: false, graph: false, grid: false },
+  opts: { lighting: true, outlines: false, graph: false, grid: false, entities: true },
   genMs: 0,
 };
 
@@ -43,6 +43,8 @@ const SLIDERS = [
   ['pillars.room_chance', 'pillars', 0, 1, 0.05],
   ['pools.water_chance', '≈ water', 0, 1, 0.05],
   ['pools.lava_chance', '♨ lava', 0, 1, 0.05],
+  ['entities.treasure_chance', '◆ treasure', 0, 1, 0.05],
+  ['entities.monster_chance', '● monsters', 0, 1, 0.05],
 ];
 
 function getPath(obj, path) {
@@ -95,10 +97,14 @@ function updateReadout() {
   const rooms = env.regions.filter((r) => r.kind === 'Room' && r.cells.length > 0).length;
   const corrs = env.regions.filter((r) => r.kind === 'Corridor').length;
   const doors = countTiles(env, 2);
+  const ents = env.entities || [];
+  const byKind = (k) => ents.filter((e) => e.kind === k).length;
   readout.querySelector('#stats').innerHTML =
     `seed <b>${env.seed}</b> · ${env.width}×${env.height} · ` +
     `<b>${rooms}</b> rooms · ${corrs} corridors · ${doors} doors · ` +
-    `${env.edges.length} edges · gen <b>${state.genMs.toFixed(1)}</b> ms`;
+    `gen <b>${state.genMs.toFixed(1)}</b> ms<br>` +
+    `◆ <b>${byKind('Treasure')}</b> treasure · ● <b>${byKind('Monster')}</b> monsters · ` +
+    `${byKind('Entrance')} entrance · ${byKind('Exit')} exit`;
 }
 
 // --- controls UI ---------------------------------------------------------
@@ -144,7 +150,7 @@ function buildControls() {
   // Toggles.
   const togRow = document.createElement('div');
   togRow.className = 'row toggles';
-  togRow.innerHTML = ['lighting', 'outlines', 'graph', 'grid']
+  togRow.innerHTML = ['lighting', 'entities', 'outlines', 'graph', 'grid']
     .map((k) => `<label class="tog"><input type="checkbox" data-opt="${k}" ${state.opts[k] ? 'checked' : ''}>${k}</label>`)
     .join('');
   panel.appendChild(togRow);
@@ -195,6 +201,7 @@ window.reikhelm = {
     pillarTiles: state.env ? countTiles(state.env, 3) : 0,
     water: state.env ? countTiles(state.env, 4) : 0,
     lava: state.env ? countTiles(state.env, 5) : 0,
+    entities: state.env ? state.env.entities.length : 0,
     ok: !!state.env }),
 };
 

reikhelm-web/render.js

@@ -25,6 +25,10 @@ const PAL = {
   waterShallow: [66, 120, 152], // sheen
   lavaCrust: [120, 32, 10],   // cooled crust
   lavaHot: [255, 152, 48],    // molten core
+  entrance: [96, 214, 124], // green beacon
+  exit: [96, 200, 232],     // cyan portal
+  treasure: [242, 202, 92], // gold
+  monster: [226, 84, 72],   // crimson
   outlineRoom: 'rgba(122, 184, 240, 0.85)',
   outlineCorr: 'rgba(150, 150, 170, 0.40)',
   edge: 'rgba(232, 96, 84, 0.85)',
@@ -336,9 +340,79 @@ export function renderMap(ctx, vw, vh, env, opts = {}) {
   if (opts.graph) drawGraph(ctx, regions, edges, layout);
   if (opts.grid) drawGrid(ctx, layout);
 
+  // 6) Entities (entrance/exit/treasure/monsters) — only exist on the final
+  //    stage, drawn on top of everything as the dungeon's inhabitants.
+  const lastStage = (env.snapshots?.length ?? 1) - 1;
+  const isFinal = (opts.stage ?? lastStage) >= lastStage;
+  if (isFinal && opts.entities !== false && env.entities) {
+    drawEntities(ctx, env.entities, layout);
+  }
+
   return layout;
 }
 
+// Draw each entity as an iconic marker centered in its cell, with a soft glow so
+// it reads over the lit floor.
+function drawEntities(ctx, entities, { cell, ox, oy }) {
+  const r = Math.max(2.5, cell * 0.3);
+  const center = (e) => [ox + e.at[0] * cell + cell / 2, oy + e.at[1] * cell + cell / 2];
+  const glow = (cx, cy, col, rad) => {
+    const g = ctx.createRadialGradient(cx, cy, 0, cx, cy, rad);
+    g.addColorStop(0, `rgba(${col[0]},${col[1]},${col[2]},0.55)`);
+    g.addColorStop(1, `rgba(${col[0]},${col[1]},${col[2]},0)`);
+    ctx.fillStyle = g;
+    ctx.beginPath();
+    ctx.arc(cx, cy, rad, 0, Math.PI * 2);
+    ctx.fill();
+  };
+
+  for (const e of entities) {
+    const [cx, cy] = center(e);
+    switch (e.kind) {
+      case 'Entrance': {
+        glow(cx, cy, PAL.entrance, r * 2.4);
+        ctx.fillStyle = rgb(PAL.entrance);
+        ctx.beginPath(); ctx.arc(cx, cy, r, 0, Math.PI * 2); ctx.fill();
+        ctx.fillStyle = 'rgba(255,255,255,0.92)';
+        ctx.beginPath(); ctx.arc(cx, cy, r * 0.42, 0, Math.PI * 2); ctx.fill();
+        break;
+      }
+      case 'Exit': {
+        glow(cx, cy, PAL.exit, r * 2.6);
+        ctx.strokeStyle = rgb(PAL.exit);
+        ctx.lineWidth = Math.max(1.5, r * 0.34);
+        ctx.beginPath(); ctx.arc(cx, cy, r, 0, Math.PI * 2); ctx.stroke();
+        ctx.beginPath(); ctx.arc(cx, cy, r * 0.45, 0, Math.PI * 2); ctx.stroke();
+        break;
+      }
+      case 'Treasure': {
+        glow(cx, cy, PAL.treasure, r * 2.0);
+        ctx.save();
+        ctx.translate(cx, cy);
+        ctx.rotate(Math.PI / 4); // diamond
+        ctx.fillStyle = rgb(PAL.treasure);
+        const s = r * 1.25;
+        ctx.fillRect(-s / 2, -s / 2, s, s);
+        ctx.fillStyle = 'rgba(255,255,255,0.85)';
+        ctx.fillRect(-s / 2, -s / 2, s * 0.32, s * 0.32);
+        ctx.restore();
+        break;
+      }
+      case 'Monster': {
+        glow(cx, cy, PAL.monster, r * 1.9);
+        ctx.fillStyle = rgb(PAL.monster);
+        ctx.beginPath(); ctx.arc(cx, cy, r * 0.92, 0, Math.PI * 2); ctx.fill();
+        // two dark "eyes"
+        ctx.fillStyle = 'rgba(20,8,8,0.92)';
+        const eye = Math.max(0.7, r * 0.2);
+        ctx.beginPath(); ctx.arc(cx - r * 0.34, cy - r * 0.12, eye, 0, Math.PI * 2); ctx.fill();
+        ctx.beginPath(); ctx.arc(cx + r * 0.34, cy - r * 0.12, eye, 0, Math.PI * 2); ctx.fill();
+        break;
+      }
+    }
+  }
+}
+
 // Trace each region's true cell-set boundary (shows polygonal room shapes).
 function drawOutlines(ctx, regions, { cell, ox, oy }) {
   for (const r of regions) {