Add level 5: Chambers (dictionaries + lists)

Top-level `chambers:` mapping; each chamber name maps to an item list.
2-3 chambers, 2-3 items each, drawn from typed pools. Deterministic per
seed via ChaCha8Rng XOR'd with 0x..05.

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/l05_dict_list.rs

@@ -0,0 +1,99 @@
+//! Level 5 — dictionaries AND lists. Each chamber keeps its own inventory.
+//!
+//! Paired design note: `l05.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 DictList;
+
+const CHAMBERS: &[&str] = &[
+    "armory", "pantry", "library", "vault", "kitchen", "cellar",
+];
+const ITEMS: &[&str] = &[
+    "sword", "shield", "bread", "water", "tome", "scroll", "gem", "coin", "dagger", "potion",
+];
+
+#[derive(Serialize)]
+struct DescCtx {
+    chambers: Vec<ChamberDesc>,
+}
+
+#[derive(Serialize)]
+struct ChamberDesc {
+    name: String,
+    items: Vec<String>,
+}
+
+impl Level for DictList {
+    fn id(&self) -> u8 {
+        5
+    }
+
+    fn name(&self) -> &'static str {
+        "Chambers"
+    }
+
+    fn generate(&self, seed: u64) -> Generated {
+        let mut rng = ChaCha8Rng::seed_from_u64(seed ^ 0x0000_0000_0000_0005);
+        let n = rng.gen_range(2..=3);
+        let chamber_names: Vec<&'static str> =
+            CHAMBERS.choose_multiple(&mut rng, n).copied().collect();
+
+        let mut inner = Mapping::new();
+        let mut desc_chambers = Vec::new();
+        for name in &chamber_names {
+            let item_n = rng.gen_range(2..=3);
+            let items: Vec<&'static str> =
+                ITEMS.choose_multiple(&mut rng, item_n).copied().collect();
+            let seq: Sequence = items
+                .iter()
+                .map(|i| Value::String((*i).to_string()))
+                .collect();
+            inner.insert(Value::String((*name).to_string()), Value::Sequence(seq));
+            desc_chambers.push(ChamberDesc {
+                name: (*name).to_string(),
+                items: items.iter().map(|s| s.to_string()).collect(),
+            });
+        }
+
+        let mut top = Mapping::new();
+        top.insert(
+            Value::String("chambers".to_string()),
+            Value::Mapping(inner),
+        );
+
+        let target_yaml =
+            serde_yaml::to_string(&Value::Mapping(top)).expect("serialise mapping");
+
+        let mut d = Describer::new();
+        d.register(
+            "l05",
+            "Several chambers branch off, each with its own inventory:\n\
+             {% for c in chambers %}\n{{ c.name }}:{% for it in c.items %}\n  - {{ it }}{% endfor %}\n{% endfor %}\n\
+             💡 Wrap the whole tree under a `chambers:` key — a dict of lists.",
+        )
+        .expect("register template");
+        let description = d
+            .render(
+                "l05",
+                &DescCtx {
+                    chambers: desc_chambers,
+                },
+            )
+            .expect("render template");
+
+        Generated {
+            target_yaml,
+            description,
+            flavor: "🏛 You enter a hall. Doors lead to many chambers.".to_string(),
+        }
+    }
+}

src/levels/mod.rs

@@ -13,6 +13,7 @@
 pub mod l01_minimum;
 pub mod l02_kv;
 pub mod l03_dict;
+pub mod l05_dict_list;
 
 use serde::{Deserialize, Serialize};