Package weight, payload capacity and per-kg payout (ISS-045)

Packages carry a real weightKg (unit weight x count with +/-30% jitter),
plane capacity becomes maxPayloadKg instead of 6 slots, load validation
sums cargo weight against the payload, and the payout gains a per-kg part.
Loadout display shows tonnage; OpenAPI swaps CatalogEntry.capacity for
maxPayloadKg and adds PackageState.weightKg.

lib/game/actions.ts

@@ -20,7 +20,7 @@ import { HUB_ICAO } from './seed';
 // GameActionError carrying the HTTP status:
 //   404 — unknown entity id
 //   409 — valid ids but the current state forbids the action (wrong package/plane
-//         status, plane not at origin, no free slot, insufficient fuel/funds, last plane)
+//         status, plane not at origin, no payload room, insufficient fuel/funds, last plane)
 //   400 — bad input that isn't an existence problem (unknown airport/model)
 
 export class GameActionError extends Error {
@@ -43,8 +43,9 @@ async function airportByIcao(icao: string): Promise<{ icao: string; lat: number;
 // --- Load (POST /api/packages/:id/load {planeId}) ---
 
 // open → loaded, bound to the plane. The plane must be GROUNDED at the package's
-// origin with a free slot (slots = packages 'loaded' or 'expired' on it — expired
-// cargo keeps occupying its space until delivered/abandoned).
+// origin with enough payload room (v0.27.0: used kg = sum of weightKg over packages
+// 'loaded' or 'expired' on it — expired cargo keeps occupying its space until
+// delivered/abandoned).
 export async function loadPackage(inst: GameDb, packageId: string, planeId: string): Promise<void> {
   const [pkgRows, planeRows] = await Promise.all([
     inst.db.select().from(schema.packages).where(eq(schema.packages.id, packageId)),
@@ -69,13 +70,12 @@ export async function loadPackage(inst: GameDb, packageId: string, planeId: stri
 
   const type = PLANE_TYPES[plane.model];
   if (!type) throw new Error(`unknown plane model ${plane.model}`); // → 500, cannot happen for seeded data
-  const occupied = (
-    await inst.db.select().from(schema.packages).where(
-      and(inArray(schema.packages.status, ['loaded', 'expired']), eq(schema.packages.planeId, plane.id)),
-    )
-  ).length;
-  if (occupied >= type.capacity) {
-    throw new GameActionError(409, `no free slots: the ${type.name} carries ${occupied}/${type.capacity} packages`);
+  const occupied = await inst.db.select({ weightKg: schema.packages.weightKg }).from(schema.packages).where(
+    and(inArray(schema.packages.status, ['loaded', 'expired']), eq(schema.packages.planeId, plane.id)),
+  );
+  const usedKg = occupied.reduce((sum, r) => sum + (r.weightKg ?? 0), 0);
+  if (usedKg + pkg.weightKg > type.maxPayloadKg) {
+    throw new GameActionError(409, `no payload room: the ${type.name} carries ${Math.round(usedKg)}/${type.maxPayloadKg} kg`);
   }
 
   await inst.db.update(schema.packages)