Name the Battle Tower's ZABOROWSKI instead of refusing the battle

BattleTowerTrainers' names are ten bytes padded with "@" only when
shorter, and the cartridge copies the ten bytes to wOTPlayerName before
adding the terminator. The port read the name as an "@"-terminated
string, so drawing ZABOROWSKI (trainer 5) threw "Unterminated string."
and the challenge was refused.

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

src/game/scripts/battle-tower.ts

@@ -2,7 +2,7 @@ import { JOHTO, RAM, WRAM } from "../rom/profile";
 import { maxPP, validPartyMon, type PartyMon } from "../party/pokemon";
 import type { PokemonData } from "../rom/pokemon";
 import { DIRECTION_ORDER, type Direction } from "../world/types";
-import { readString } from "./text";
+import { readFixedString, readString } from "./text";
 import type { Gen, SpecialContext } from "./special-context";
 
 /** BATTLETOWER_* (constants/battle_tower_constants.asm). */
@@ -209,7 +209,9 @@ export function loadOpponent(c: SpecialContext, bt: BattleTowerState): BattleTow
   const trainer = sample(c, BATTLE_TOWER.uniqueTrainers, (index) => bt.trainers.includes(index));
   bt.trainers[bt.beaten] = trainer;
   const entry = JOHTO.BattleTowerTrainers + trainer * TRAINER_ENTRY;
-  const name = readString(r, entry, c.text(), TRAINER_ENTRY - 1);
+  // Copied to wOTPlayerName with a "@" after its ten bytes: ZABOROWSKI
+  // fills them.
+  const name = readFixedString(r, entry, c.text(), TRAINER_ENTRY - 1);
   const trainerClass = r.byte(entry + TRAINER_ENTRY - 1);
   // LoadRandomBattleTowerMon: wBT_OTMon1-3 start as species 0 and item $ff.
   const species = [0, 0, 0],

src/game/scripts/text.ts

@@ -153,6 +153,25 @@ function character(code: number, context: TextContext): string | undefined {
   return CHARACTERS[code];
 }
 
+/** Decode a name of at most `length` characters, as CopyBytes followed by
+ * a "@" leaves it: one that fills its field has no terminator of its own. */
+export function readFixedString(
+  reader: RomReader,
+  start: number,
+  context: TextContext,
+  length: number,
+): string {
+  let output = "";
+  for (let p = start; p < start + length; p++) {
+    const code = reader.byte(p);
+    if (code === 0x50) break;
+    const value = character(code, context);
+    if (value === undefined) throw new UnsupportedText(p, code);
+    output += value;
+  }
+  return output;
+}
+
 /** Decode a plain "@"-terminated string such as a name or item label. */
 export function readString(
   reader: RomReader,

tests/battle-tower.test.ts

@@ -3,7 +3,8 @@ import { existsSync, readFileSync } from "node:fs";
 import { CrystalAssets } from "../src/game/rom/assets";
 import { GameWorld } from "../src/game/world/world";
 import { calcStats, generatePartyMon, maxPP, type PartyMon } from "../src/game/party/pokemon";
-import { CHALLENGE } from "../src/game/scripts/battle-tower";
+import { CHALLENGE, emptyBattleTowerState, loadOpponent } from "../src/game/scripts/battle-tower";
+import type { SpecialContext } from "../src/game/scripts/special-context";
 import { Playthrough } from "./playthrough-driver";
 
 const romPath =
@@ -88,6 +89,26 @@ describe.skipIf(!existsSync(romPath))("the Battle Tower with the local ROM", ()
     expect(p.world.notice, p.world.diagnostic).toBe("");
   };
 
+  it("names a trainer whose name fills all ten characters", () => {
+    // BattleTowerTrainers' sixth entry, ZABOROWSKI, has no "@" of its own.
+    let seed = 5;
+    const context = {
+      reader: assets!.reader,
+      data: assets!.pokemon,
+      random: () => {
+        seed = (seed * 1103515245 + 12345) >>> 0;
+        return (seed >>> 16) & 255;
+      },
+      text: () => ({ player: "KAWA", rival: "SILVER", mom: "MOM", strings: {}, weekday: "SUNDAY" }),
+    } as unknown as SpecialContext;
+    const names = new Map<number, string>();
+    for (let draw = 0; draw < 300 && !names.has(5); draw++) {
+      const opponent = loadOpponent(context, { ...emptyBattleTowerState(), levelGroup: 1 });
+      names.set(opponent.trainer, opponent.name);
+    }
+    expect(names.get(5)).toBe("ZABOROWSKI");
+  });
+
   it("is reached from Route 40 through its gate", () => {
     const p = new Playthrough(assets!);
     p.world = new GameWorld(assets!, p.now, p.random);