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/l10_dynamic.rs

@@ -1,101 +0,0 @@
-//! Level 10 — dynamic values. The vault ledger accepts numbers and
-//! dates in many forms.
-//!
-//! Paired design note: `l10.md`.
-//!
-//! The target is canonical (decimal ints, decimal float, ISO date
-//! string). The lesson is that the player can write equivalent values
-//! in hex / octal / exponent forms — all parse to the same number.
-
-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 Dynamic;
-
-#[derive(Serialize)]
-struct DescCtx {
-    gold_dec: i64,
-    gold_hex: String,
-    silver_dec: i64,
-    silver_oct: String,
-    experience: f64,
-    date: String,
-}
-
-impl Level for Dynamic {
-    fn id(&self) -> u8 {
-        10
-    }
-
-    fn name(&self) -> &'static str {
-        "Vault Ledger"
-    }
-
-    fn generate(&self, seed: u64) -> Generated {
-        let mut rng = ChaCha8Rng::seed_from_u64(seed ^ 0x0000_0000_0000_000A);
-
-        let gold = rng.gen_range(0x100..=0xFFFi64);
-        let silver = rng.gen_range(0o100..=0o777i64);
-        // Fractional float so the canonical serialisation keeps the `.5`.
-        let experience = rng.gen_range(10..=99) as f64 + 0.5;
-        let year = rng.gen_range(1100..=2050i64);
-        let month = rng.gen_range(1..=12i64);
-        let day = rng.gen_range(1..=28i64);
-        let date = format!("{year:04}-{month:02}-{day:02}");
-
-        let mut vault = Mapping::new();
-        vault.insert(Value::String("gold".to_string()), Value::from(gold));
-        vault.insert(Value::String("silver".to_string()), Value::from(silver));
-        vault.insert(
-            Value::String("experience".to_string()),
-            Value::from(experience),
-        );
-        vault.insert(
-            Value::String("date".to_string()),
-            Value::String(date.clone()),
-        );
-
-        let mut top = Mapping::new();
-        top.insert(Value::String("vault".to_string()), Value::Mapping(vault));
-
-        let target_yaml =
-            serde_yaml::to_string(&Value::Mapping(top)).expect("serialise mapping");
-
-        let mut d = Describer::new();
-        d.register(
-            "l10",
-            "The vault ledger demands its values:\n\
-             gold:       {{ gold_dec }}   (try hex: 0x{{ gold_hex }})\n\
-             silver:     {{ silver_dec }} (try octal: 0o{{ silver_oct }})\n\
-             experience: {{ experience }} (any equivalent float form passes)\n\
-             date:       {{ date }}        (an ISO-8601 date string)\n\
-             💡 Any equivalent numeric form passes — what matters is the parsed value.",
-        )
-        .expect("register template");
-        let description = d
-            .render(
-                "l10",
-                &DescCtx {
-                    gold_dec: gold,
-                    gold_hex: format!("{:X}", gold),
-                    silver_dec: silver,
-                    silver_oct: format!("{:o}", silver),
-                    experience,
-                    date,
-                },
-            )
-            .expect("render template");
-
-        Generated {
-            target_yaml,
-            description,
-            flavor: "🪙 A vault ledger awaits in many ciphers.".to_string(),
-        }
-    }
-}

src/levels/mod.rs

@@ -13,7 +13,7 @@
 pub mod l01_minimum;
 pub mod l02_kv;
 pub mod l03_dict;
-pub mod l10_dynamic;
+pub mod l04_list;
 
 use serde::{Deserialize, Serialize};