Add level 4: The Chest (lists)

Top-level `chest:` key with a 3-5 item sequence drawn from a small pool.
Per-seed deterministic via ChaCha8Rng XOR'd with 0x..04. Description
rendered with tera; flavor uses a 📦 emoji.

Not wired into levels::registry() yet — integration belongs to a follow-up.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/levels/l04_list.rs

@@ -0,0 +1,71 @@
+//! Level 4 — lists. A chest of loot lies open before you.
+//!
+//! Paired design note: `l04.md`.
+
+use rand::seq::SliceRandom;
+use rand::{Rng, SeedableRng};
+use rand_chacha::ChaCha8Rng;
+use serde::Serialize;
+use serde_yaml::{Mapping, Sequence, Value};
+
+use crate::describe::Describer;
+
+use super::{Generated, Level};
+
+pub struct List;
+
+const ITEMS: &[&str] = &[
+    "sword", "torch", "rope", "bread", "dagger", "scroll", "gem", "coin", "potion", "shield",
+];
+
+#[derive(Serialize)]
+struct DescCtx {
+    items: Vec<String>,
+}
+
+impl Level for List {
+    fn id(&self) -> u8 {
+        4
+    }
+
+    fn name(&self) -> &'static str {
+        "The Chest"
+    }
+
+    fn generate(&self, seed: u64) -> Generated {
+        let mut rng = ChaCha8Rng::seed_from_u64(seed ^ 0x0000_0000_0000_0004);
+        let n = rng.gen_range(3..=5);
+        let items: Vec<&'static str> = ITEMS.choose_multiple(&mut rng, n).copied().collect();
+
+        let seq: Sequence = items
+            .iter()
+            .map(|i| Value::String((*i).to_string()))
+            .collect();
+
+        let mut top = Mapping::new();
+        top.insert(Value::String("chest".to_string()), Value::Sequence(seq));
+        let target_yaml =
+            serde_yaml::to_string(&Value::Mapping(top)).expect("serialise mapping");
+
+        let mut d = Describer::new();
+        d.register(
+            "l04",
+            "A chest lies open. Inside:\n{% for it in items %}- {{ it }}\n{% endfor %}\n💡 Wrap the items as a YAML list under a `chest:` key.",
+        )
+        .expect("register template");
+        let description = d
+            .render(
+                "l04",
+                &DescCtx {
+                    items: items.iter().map(|s| s.to_string()).collect(),
+                },
+            )
+            .expect("render template");
+
+        Generated {
+            target_yaml,
+            description,
+            flavor: "📦 A chest of loot lies open before you.".to_string(),
+        }
+    }
+}

src/levels/l06_anchors.rs

@@ -1,113 +0,0 @@
-//! Level 6 — anchors. Two rooms share the same trap — define it once.
-//!
-//! Paired design note: `l06.md`.
-//!
-//! Note: serde_yaml resolves aliases at parse time, so the target is
-//! emitted **expanded** (the trap dict appears in each room). Players
-//! who use anchors/aliases will produce the same parsed `Value` and
-//! pass via the semantic short-circuit. Players who paste the dict
-//! verbatim also pass.
-
-use rand::seq::SliceRandom;
-use rand::{Rng, SeedableRng};
-use rand_chacha::ChaCha8Rng;
-use serde::Serialize;
-use serde_yaml::{Mapping, Value};
-
-use crate::describe::Describer;
-
-use super::{Generated, Level};
-
-pub struct Anchors;
-
-const ROOM_NAMES: &[&str] = &["north", "south", "east", "west"];
-const TRAP_TYPES: &[&str] = &["pit", "snare", "dart", "rune"];
-
-#[derive(Serialize)]
-struct DescCtx {
-    trap_type: String,
-    trap_depth: i64,
-    trap_spikes: bool,
-    rooms: Vec<String>,
-}
-
-impl Level for Anchors {
-    fn id(&self) -> u8 {
-        6
-    }
-
-    fn name(&self) -> &'static str {
-        "Anchors"
-    }
-
-    fn generate(&self, seed: u64) -> Generated {
-        let mut rng = ChaCha8Rng::seed_from_u64(seed ^ 0x0000_0000_0000_0006);
-        let trap_type = *TRAP_TYPES.choose(&mut rng).expect("non-empty");
-        let trap_depth = rng.gen_range(10..=30i64);
-        let trap_spikes = rng.gen_bool(0.5);
-        let n_rooms = rng.gen_range(2..=3);
-        let rooms: Vec<&'static str> = ROOM_NAMES
-            .choose_multiple(&mut rng, n_rooms)
-            .copied()
-            .collect();
-
-        let mut trap = Mapping::new();
-        trap.insert(
-            Value::String("type".to_string()),
-            Value::String(trap_type.to_string()),
-        );
-        trap.insert(Value::String("depth".to_string()), Value::from(trap_depth));
-        trap.insert(
-            Value::String("spikes".to_string()),
-            Value::Bool(trap_spikes),
-        );
-
-        let mut rooms_map = Mapping::new();
-        for r in &rooms {
-            rooms_map.insert(
-                Value::String((*r).to_string()),
-                Value::Mapping(trap.clone()),
-            );
-        }
-
-        let mut top = Mapping::new();
-        top.insert(Value::String("trap".to_string()), Value::Mapping(trap));
-        top.insert(
-            Value::String("rooms".to_string()),
-            Value::Mapping(rooms_map),
-        );
-
-        let target_yaml =
-            serde_yaml::to_string(&Value::Mapping(top)).expect("serialise mapping");
-
-        let mut d = Describer::new();
-        d.register(
-            "l06",
-            "A single trap recurs through these halls:\n\
-             - type: {{ trap_type }}\n\
-             - depth: {{ trap_depth }}\n\
-             - spikes: {{ trap_spikes }}\n\
-             \n\
-             Reuse it for these rooms: {% for r in rooms %}{{ r }}{% if not loop.last %}, {% endif %}{% endfor %}.\n\
-             💡 Define `trap: &name` once and reference it as `*name` in every room.",
-        )
-        .expect("register template");
-        let description = d
-            .render(
-                "l06",
-                &DescCtx {
-                    trap_type: trap_type.to_string(),
-                    trap_depth,
-                    trap_spikes,
-                    rooms: rooms.iter().map(|s| s.to_string()).collect(),
-                },
-            )
-            .expect("render template");
-
-        Generated {
-            target_yaml,
-            description,
-            flavor: "🪤 A trap recurs through these halls.".to_string(),
-        }
-    }
-}

src/levels/mod.rs

@@ -13,7 +13,7 @@
 pub mod l01_minimum;
 pub mod l02_kv;
 pub mod l03_dict;
-pub mod l06_anchors;
+pub mod l04_list;
 
 use serde::{Deserialize, Serialize};