game_data: UnitRoster loader — per-mission battle compositions

Decode the EnumUnit tables (schema 35b8dc67) into mission rosters: the
distinct combatant `UN_*` ids for one battle, stage props (asteroids,
collision meshes) dropped. The tables aren't tagged with their stage on
disc, so `stage` is inferred from any `UN_S<NN>_…` prop id in the roster
and left None otherwise (honest — ~8 of 31 rosters self-identify).

Joined against load_units / load_vessels this gives each battle's
combatants with stats, e.g. S01 = ADAN Turret (100 HP), Attacker
(500 HP), Destroyer (10000 HP). Example `battle` prints them.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

crates/sylpheed-formats/examples/battle.rs

@@ -0,0 +1,19 @@
+use sylpheed_formats::{game_data as gd, PakArchive};
+fn main(){
+    let disc=std::env::var("SYLPHEED_DISC").unwrap();
+    let pak=PakArchive::open(format!("{disc}/dat/GP_MAIN_GAME_E.pak")).unwrap();
+    let units=gd::load_units(&pak); let vessels=gd::load_vessels(&pak);
+    let hp=|id:&str|->String{
+        units.iter().find(|u|u.id.as_deref()==Some(id)).and_then(|u|u.hp).map(|h|format!("{h:.0}hp"))
+            .or_else(||vessels.iter().find(|v|v.id.as_deref()==Some(id)).and_then(|v|v.hp).map(|h|format!("{h:.0}HP")))
+            .unwrap_or("·".into())
+    };
+    let rosters=gd::load_unit_rosters(&pak);
+    for r in rosters.iter().filter(|r|r.stage.is_some()).take(4){
+        println!("\n{} — {} combatants:", r.stage.as_deref().unwrap(), r.units.len());
+        for u in r.units.iter().filter(|u|u.contains("ADAN")).take(6){
+            let short=u.trim_start_matches("UN_").split('_').skip(1).collect::<Vec<_>>().join("_");
+            println!("   {short:32} {}", hp(u));
+        }
+    }
+}

crates/sylpheed-formats/src/game_data.rs

@@ -573,6 +573,56 @@ pub fn load_demo_messages(pak: &PakArchive) -> Vec<DemoMessage> {
     out
 }
 
+// ── Unit roster (per-mission combatants) ────────────────────────────────────────
+
+/// Schema of the per-stage `EnumUnit` roster tables.
+const ENUM_UNIT_SCHEMA: u32 = 0x35b8_dc67;
+
+/// A mission's unit roster — the craft, vessels and props that can appear in one
+/// battle (an `EnumUnit_S<NN>` table). Join the ids against [`load_units`] /
+/// [`load_vessels`] for stats. The table isn't tagged with its stage on disc, so
+/// [`stage`](UnitRoster::stage) is inferred from any `S<NN>_`-prefixed prop id in
+/// the roster (asteroid collision meshes etc.) and is `None` when none is present.
+#[derive(Debug, Clone)]
+pub struct UnitRoster {
+    pub stage: Option<String>,
+    /// Distinct combatant unit ids (`UN_*`), excluding stage props (asteroids,
+    /// collision meshes).
+    pub units: Vec<String>,
+}
+
+/// Load every mission unit roster from a pak.
+pub fn load_unit_rosters(pak: &PakArchive) -> Vec<UnitRoster> {
+    let mut out = Vec::new();
+    for e in pak.entries() {
+        let Ok(b) = pak.read(e) else { continue };
+        let Ok(o) = IdxdObject::parse(&b) else { continue };
+        if o.schema_hash != ENUM_UNIT_SCHEMA {
+            continue;
+        }
+        let ids: Vec<&str> = o.tokens().iter().filter(|s| s.starts_with("UN_")).map(String::as_str).collect();
+        // Stage tag from an `UN_S<NN>_…` prop id (e.g. UN_S01_Asteroid_cmesh_…).
+        let stage = ids.iter().find_map(|s| {
+            let r = s.trim_start_matches("UN_");
+            let bytes = r.as_bytes();
+            (r.len() >= 3 && bytes[0] == b'S' && bytes[1].is_ascii_digit() && bytes[2].is_ascii_digit())
+                .then(|| r[..3].to_string())
+        });
+        // Combatants: drop the stage props, dedup preserving order.
+        let mut units = Vec::new();
+        for id in ids {
+            let prop = id.contains("Asteroid") || id.contains("cmesh") || id.contains("_Box");
+            if !prop && !units.iter().any(|u| u == id) {
+                units.push(id.to_string());
+            }
+        }
+        if !units.is_empty() {
+            out.push(UnitRoster { stage, units });
+        }
+    }
+    out
+}
+
 // ── Generic record access (any of the ~105 schemas) ─────────────────────────────
 
 /// A generically-decoded IDXD record: its table name, schema id, identity, and
@@ -743,6 +793,21 @@ mod tests {
         assert!(m.page_keys.iter().all(|k| k.starts_with(&m.id)));
     }
 
+    #[test]
+    fn loads_unit_rosters() {
+        let Some(pak) = pak() else { return };
+        let rosters = load_unit_rosters(&pak);
+        assert!(rosters.len() > 20, "expected many rosters, got {}", rosters.len());
+        // At least a few tag their stage; all rosters carry combatants, no props.
+        assert!(rosters.iter().filter(|r| r.stage.is_some()).count() >= 4);
+        assert!(rosters.iter().all(|r| {
+            !r.units.is_empty() && r.units.iter().all(|u| !u.contains("Asteroid"))
+        }));
+        // A roster tagged S01 exists and names the player's Delta Saber.
+        let s01 = rosters.iter().find(|r| r.stage.as_deref() == Some("S01"));
+        assert!(s01.is_some_and(|r| r.units.iter().any(|u| u.contains("DeltaSaber"))));
+    }
+
     #[test]
     fn generic_records_read_any_schema() {
         let Some(pak) = pak() else { return };