WI-1: injectable RNG - request_rng() single construction point (StdRng::from_os_rng), thread rng through create_character and run_adventure, seeded determinism test (PSP1, issue #1)

crates/sb-core/src/character.rs

@@ -126,10 +126,15 @@ pub fn training_cost(stat: i64) -> i32 {
     (5.0_f64 * 1.3_f64.powi(scaled)) as i32
 }
 
-pub fn create_character(user_id: u32, name: String, race: Race, class: Class) -> Character {
-    let mut rng = rand::rng();
+pub fn create_character(
+    rng: &mut impl rand::Rng,
+    user_id: u32,
+    name: String,
+    race: Race,
+    class: Class,
+) -> Character {
     let class_str = class.as_str().to_string();
-    let stats = roll_stats(&mut rng, &race);
+    let stats = roll_stats(rng, &race);
     let max_hp = calc_max_hp(&class, &stats);
     let max_energy = calc_max_energy(&class);
     let max_nerve = calc_max_nerve(&class);
@@ -412,4 +417,28 @@ mod tests {
         assert!(dwarf.strength > human.strength);
         assert!(dwarf.intelligence < human.intelligence);
     }
+
+    #[test]
+    fn create_character_is_deterministic_under_seeded_rng() {
+        use rand::SeedableRng;
+        let first = create_character(
+            &mut rand::rngs::StdRng::seed_from_u64(42),
+            7,
+            "Twin".into(),
+            Race::Human,
+            Class::Warrior,
+        );
+        let second = create_character(
+            &mut rand::rngs::StdRng::seed_from_u64(42),
+            7,
+            "Twin".into(),
+            Race::Human,
+            Class::Warrior,
+        );
+        assert_eq!(format!("{:?}", first.stats), format!("{:?}", second.stats));
+        assert_eq!(first.hp, second.hp);
+        assert_eq!(first.max_hp, second.max_hp);
+        assert_eq!(first.energy, second.energy);
+        assert_eq!(first.nerve, second.nerve);
+    }
 }