Port the fishing rods and wild Magikarp

The Old, Good and Super Rods run FishFunction facing water: the map's fish
group and Fish pick no fish, no bite, or a Pokémon from FishGroups and the
time of day's TimeFishGroups. The player casts and jiggles with the
fishing frames drawn from LoadFishingGFX's tiles, shows "!" on a bite, and
the hooked Pokémon attacks as BATTLETYPE_FISH. Facing pieces now use
signed offsets, which the rod above and left of the player needs.

Wild Magikarp no longer stop a battle: LoadEnemyMon redraws their DVs
through CalcMagikarpLength and its filters, as the original does. The
length routine matches the original in the reference emulator.

Part of #27

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

tests/reference-parity.spec.ts

@@ -6,6 +6,7 @@ import {
   Battle,
   applyTypeMatchups,
   calculateDamage,
+  magikarpLength,
   restoreHealth,
   restoredPP,
   sendOutText,
@@ -638,3 +639,75 @@ test("native switch texts, healing, PP, happiness and CalcPlayerStats match the
     ).toEqual(results.stats[index]);
   });
 });
+
+test("native Magikarp lengths match CalcMagikarpLength", async ({ page }) => {
+  test.skip(
+    !existsSync(romPath) || !existsSync(symbolsPath),
+    "Requires the local user ROM and the private PRET rebuild.",
+  );
+  const { at, routine } = loadSymbols();
+  const reader = new CrystalAssets(new Uint8Array(readFileSync(romPath))).reader;
+  let seed = 0x4a39;
+  const next = (limit: number) => {
+    seed = (seed * 1103515245 + 12345) >>> 0;
+    return (seed >>> 8) % limit;
+  };
+  // Random DVs and IDs, plus indexes below 10 and at the table's edges.
+  const cases = [
+    ...Array.from({ length: 1500 }, () => ({ dvs: next(0x10000), id: next(0x10000) })),
+    ...[0x0000, 0x0009, 0x000a, 0x00ff, 0x0100, 0xfdff, 0xfe00, 0xff00, 0xffff].map((dvs) => ({
+      dvs,
+      id: 0,
+    })),
+  ];
+  await openReference(page);
+  const addresses = {
+    calc: routine("CalcMagikarpLength"),
+    length: at("wMagikarpLength"),
+  };
+  const results = await page.evaluate(
+    async ({ addresses, cases }) => {
+      const { BinjgbEmulator } = await import("/src/emulator/binjgb.ts");
+      const file = (document.querySelector("#reference-fixture") as HTMLInputElement).files![0];
+      const reference = new BinjgbEmulator();
+      await reference.load(new Uint8Array(await file.arrayBuffer()), document.createElement("canvas"));
+      const write = (address: number, value: number) => reference.writeMemory(address, value & 0xff);
+      // Trampoline: DI; SP=$c7fe; switch to the routine's bank; set BC (the
+      // ID) and DE (the DVs); CALL CalcMagikarpLength; write a sentinel; loop.
+      const dvs = 0xc100,
+        id = 0xc102;
+      const program = [
+        0xf3, 0x31, 0xfe, 0xc7, 0x3e, addresses.calc.bank, 0xe0, 0x9d, 0xea, 0x00, 0x20,
+        0x01, id & 0xff, id >> 8, 0x11, dvs & 0xff, dvs >> 8,
+        0xcd, addresses.calc.address & 0xff, addresses.calc.address >> 8,
+        0x3e, 0x42, 0xea, 0xff, 0xc6, 0x18, 0xfe,
+      ];
+      write(0xff70, 1);
+      const lengths = cases.map((input) => {
+        write(dvs, input.dvs >> 8);
+        write(dvs + 1, input.dvs);
+        write(id, input.id >> 8);
+        write(id + 1, input.id);
+        write(0xc6ff, 0);
+        program.forEach((value, index) => write(0xc000 + index, value));
+        reference.setProgramCounter(0xc000);
+        reference.advanceFrames(2);
+        return {
+          returned: reference.readMemory(0xc6ff) === 0x42,
+          feet: reference.readMemory(addresses.length),
+          inches: reference.readMemory(addresses.length + 1),
+        };
+      });
+      reference.dispose();
+      return lengths;
+    },
+    { addresses, cases },
+  );
+  cases.forEach((input, index) => {
+    const { returned, ...original } = results[index];
+    expect(returned, `case ${index} returned`).toBe(true);
+    expect(magikarpLength(reader, input.dvs, input.id), JSON.stringify(input)).toEqual(original);
+  });
+  const lengths = new Set(results.map(({ feet, inches }) => feet * 12 + inches));
+  expect(lengths.size).toBeGreaterThan(30);
+});