Port the Johto badge stat boosts (#31)

BadgeStatBoosts runs where the original calls it: when a Pokémon is sent out, after an in-battle level-up, and in CalcPlayerStats. It keeps the PlainBadge/MineralBadge swap and the Glacier Badge's Special Defense register bug. A transformed Pokémon that levels up now keeps its copied stats.

The reference emulator compares all 256 badge bytes over 28 stat sets per browser against the unmodified routine.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/reference-badges.spec.ts

@@ -0,0 +1,69 @@
+import { test, expect } from "@playwright/test";
+import { existsSync } from "node:fs";
+import { romPath, symbolsPath, loadSymbols, openReference } from "./reference-fixture";
+
+test.skip(!existsSync(romPath) || !existsSync(symbolsPath), "Needs private ROM and reference symbols.");
+test("badge stat boosts match the original for every Johto badge byte", async ({ page }) => {
+  const { at, routine } = loadSymbols();
+  const addresses = {
+    romBank: at("hROMBank"),
+    badges: at("wJohtoBadges"),
+    linkMode: at("wLinkMode"),
+    tower: at("wInBattleTowerBattle"),
+    stats: at("wBattleMonAttack"),
+  };
+  const boosts = routine("BadgeStatBoosts");
+  await openReference(page);
+  const result = await page.evaluate(async ({ a, boosts }) => {
+    const { BinjgbEmulator } = await import("/src/emulator/binjgb.ts");
+    const { CrystalAssets } = await import("/src/game/rom/assets.ts");
+    const { Battle } = await import("/src/game/battle/battle.ts");
+    const rom = new Uint8Array(await (document.querySelector("#reference-fixture") as HTMLInputElement).files![0].arrayBuffer());
+    const assets = new CrystalAssets(rom);
+    const reference = new BinjgbEmulator();
+    await reference.load(rom, document.createElement("canvas"));
+    const write = (p: number, v: number) => reference.writeMemory(p, v & 255);
+    const read = (p: number) => reference.readMemory(p);
+    // DI; SP=$c7fe; select the bank; CALL BadgeStatBoosts; sentinel; loop.
+    // The sentinel lives in audio RAM, away from the battle variables.
+    const program = [0xf3, 0x31, 0xfe, 0xc7, 0x3e, boosts.bank, 0xe0, a.romBank & 255, 0xea, 0, 0x20,
+      0xcd, boosts.address & 255, boosts.address >> 8, 0x3e, 0x42, 0xea, 0xf0, 0xc0, 0x18, 0xfe];
+    // Around the cap, a range of Special Attack values for the Glacier
+    // Badge's register bug, and small stats.
+    const statSets = [
+      [1, 2, 3, 4, 5],
+      [10, 20, 30, 40, 50],
+      [887, 888, 889, 900, 998],
+      [999, 999, 999, 999, 999],
+      ...Array.from({ length: 24 }, (_, i) => [100, 150, 200, 180 + i * 30, 300]),
+    ];
+    const failures: unknown[] = [];
+    let compared = 0;
+    for (let badges = 0; badges < 256; badges++)
+      for (const stats of statSets) {
+        const battle = new Battle({
+          data: assets.pokemon, party: [], pokedex: { seen: new Set(), caught: new Set() }, playerId: 1,
+          playerName: "CHRIS", timeOfDay: 1, random: () => 0, text: () => ({}) as never, johtoBadges: badges,
+        });
+        battle.player.mon = { stats: [...stats] } as never;
+        (battle as unknown as { badgeStatBoosts(): void }).badgeStatBoosts();
+        write(a.badges, badges);
+        write(a.linkMode, 0);
+        write(a.tower, 0);
+        stats.forEach((value, i) => { write(a.stats + i * 2, value >> 8); write(a.stats + i * 2 + 1, value); });
+        write(0xc0f0, 0);
+        program.forEach((value, i) => write(0xc000 + i, value));
+        reference.setProgramCounter(0xc000);
+        reference.advanceFrames(1);
+        if (read(0xc0f0) !== 0x42) throw Error("BadgeStatBoosts did not return");
+        const original = stats.map((_, i) => (read(a.stats + i * 2) << 8) | read(a.stats + i * 2 + 1));
+        const native = battle.player.mon.stats;
+        if (original.some((value, i) => value !== native[i])) failures.push({ badges, stats, original, native });
+        compared++;
+      }
+    reference.dispose();
+    return { compared, failures: failures.slice(0, 5), count: failures.length };
+  }, { a: addresses, boosts });
+  expect(result.compared).toBe(256 * 28);
+  expect(result, JSON.stringify(result)).toMatchObject({ count: 0 });
+});