working through a review

src/lib/encounter-budget.ts

@@ -62,3 +62,45 @@ export const DIFFICULTY_COLOR: Record<Difficulty, string> = {
   Hard: "var(--color-gold-bright)",
   Deadly: "var(--color-danger)",
 };
+
+// ─── Self-check (run: node scripts/check-encounter-budget.ts) ────
+// ponytail: the smallest thing that fails if the budget math breaks. No
+// framework — plain asserts. Verifies the per-level table scales, the
+// party-size multiplier, level clamping, and the XP→difficulty bucketing
+// (the boundary the DMG relies on: a budget-equal XP is the *next* tier).
+function assert(cond: boolean, msg: string): void {
+  if (!cond) throw new Error(`encounter-budget self-check failed: ${msg}`);
+}
+
+export function demo(): void {
+  // Level 5, 4 PCs — DMG p.82 per-character: Easy 250 / Med 500 / Hard 750 / Deadly 1100.
+  const b = encounterBudget(5, 4);
+  assert(b.easy === 1000, "L5×4 easy = 250×4");
+  assert(b.medium === 2000, "L5×4 medium = 500×4");
+  assert(b.hard === 3000, "L5×4 hard = 750×4");
+  assert(b.deadly === 4400, "L5×4 deadly = 1100×4");
+
+  // Solo L1 character.
+  const solo = encounterBudget(1, 1);
+  assert(solo.easy === 25 && solo.deadly === 100, "L1×1 matches table");
+
+  // Level clamps to 1..20; size clamps to >=1.
+  const low = encounterBudget(0, 1);
+  assert(low.easy === 25, "level clamps up to 1");
+  const high = encounterBudget(99, 1);
+  assert(high.deadly === 12700, "level clamps down to 20");
+  const zero = encounterBudget(5, 0);
+  assert(zero.medium === 500, "size clamps up to 1");
+
+  // difficultyForXp: budget-equal XP lands in the *next* tier up (>=, not >),
+  // and anything below the easy floor is still Easy (never undefined).
+  const d = encounterBudget(5, 4);
+  assert(difficultyForXp(999, d) === "Easy", "below easy floor stays Easy");
+  assert(difficultyForXp(1000, d) === "Easy", "== easy budget is Easy");
+  assert(difficultyForXp(2000, d) === "Medium", "== medium budget is Medium");
+  assert(difficultyForXp(3000, d) === "Hard", "== hard budget is Hard");
+  assert(difficultyForXp(4400, d) === "Deadly", "== deadly budget is Deadly");
+  assert(difficultyForXp(9999, d) === "Deadly", "over deadly stays Deadly");
+
+  console.log("encounter-budget self-check passed ✓");
+}