Finish the opening milestone's switching, items and acceptance run

- Decode evolution lists from the ROM; all 251 match the pinned PRET source.
- Compare CalcMonStats and CalcExpAtLevel against the original routines in
  the reference emulator.
- Add a continuous opening playthrough from the intro to the catching
  tutorial, reloading a JSON save after every stage.
- Port player switching in battle: the PKMN menu, forced choices after a
  faint, Shift mode's offer and double faints, with the original texts.
- Port HP and status healing items in battle through the ROM's ItemEffects,
  HealingHPAmounts and StatusHealingActions tables.
- Add the battle party menu and the Items pocket to the UI.

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

src/main.ts

@@ -379,8 +379,11 @@ function drawPic(
 const battlePics = { foe: "", player: "" };
 let battleMenuKey = "";
 let showMoves = false;
-/** BattlePack's Balls pocket, the only pocket usable in battle so far. */
+/** BattlePack, opened on the last pocket used (wLastPocket). */
 let showPack = false;
+let packPocket: "item" | "ball" = "item";
+/** The party slot whose BattleMonMenu (SWITCH/STATS/CANCEL) is open. */
+let partyChoice: number | undefined;
 let battleCursor = 0;
 let battleSelectionKey = "";
 
@@ -460,6 +463,11 @@ function handleBattleInput(button: Button): boolean {
     showMoves = showPack = false;
     return true;
   }
+  if (button === "b" && partyChoice !== undefined) {
+    partyChoice = undefined;
+    showWorld(world);
+    return true;
+  }
   const buttons = battleButtons();
   if (!buttons.length) return false;
   if (button === "a") {
@@ -530,22 +538,38 @@ function showBattle(world: GameWorld) {
   }
   const prompt = view.prompt;
   get("battle-text").textContent =
-    prompt?.kind === "name" ? prompt.title : (view.message?.text ?? "");
+    prompt?.kind === "name"
+      ? prompt.title
+      : prompt?.kind === "party"
+        ? prompt.text
+        : (view.message?.text ?? "");
   if (prompt?.kind !== "action") showMoves = showPack = false;
-  const selectionKey = `${prompt?.kind ?? "text"}:${showMoves}:${showPack}`;
+  if (prompt?.kind !== "party") partyChoice = undefined;
+  const selectionKey = `${prompt?.kind ?? "text"}:${showMoves}:${showPack}:${partyChoice}`;
   if (selectionKey !== battleSelectionKey) {
     battleCursor = 0;
     battleSelectionKey = selectionKey;
   }
   if (prompt?.kind === "yesno") battleCursor = view.selected === 1 ? 0 : 1;
-  const balls = world.liveState.bag.balls;
+  const bag = world.liveState.bag;
+  // The Pokémon out has its live battle HP; the others their party values.
+  const party = world.liveState.party.map((mon, index) =>
+    index === view.engine.curBattleMon && own
+      ? { ...mon, hp: own.hp, status: own.status }
+      : mon,
+  );
   const key = JSON.stringify([
     prompt,
     view.selected,
     showMoves,
     showPack,
+    partyChoice,
+    packPocket,
     own?.pp,
-    balls,
+    bag.items,
+    bag.balls,
+    prompt?.kind === "party" &&
+      party.map(({ hp, status, level }) => [hp, status, level]),
     view.message?.prompt,
   ]);
   if (key === battleMenuKey) return;
@@ -610,7 +634,19 @@ function showBattle(world: GameWorld) {
         ),
       );
     } else if (showPack) {
-      balls.forEach(({ item, quantity }, slot) =>
+      for (const pocket of ["item", "ball"] as const)
+        buttons.push(
+          button(
+            data.pocketName(pocket),
+            () => {
+              packPocket = pocket;
+              showWorld(world);
+            },
+            { pressed: packPocket === pocket },
+          ),
+        );
+      const slots = packPocket === "item" ? bag.items : bag.balls;
+      slots.forEach(({ item, quantity }, slot) =>
         buttons.push(
           button(
             data.itemName(item),
@@ -622,10 +658,11 @@ function showBattle(world: GameWorld) {
           ),
         ),
       );
-      if (!balls.length)
+      if (!slots.length)
         buttons.push(
-          button("No BALLS", () => {}, {
-            disabled: "The BALL pocket is empty.",
+          button("Empty", () => {}, {
+            disabled: `The ${data.pocketName(packPocket)} is empty.`,
+            wide: true,
           }),
         );
       buttons.push(
@@ -644,9 +681,7 @@ function showBattle(world: GameWorld) {
           showMoves = true;
           showWorld(world);
         }),
-        button("PKMN", () => {}, {
-          disabled: "Switching Pokémon is not ported yet.",
-        }),
+        button("PKMN", () => runtime.battleAction({ action: "pkmn" })),
         button("PACK", () => {
           showPack = true;
           showWorld(world);
@@ -663,6 +698,45 @@ function showBattle(world: GameWorld) {
         pressed: view.selected === 0,
       }),
     );
+  } else if (prompt?.kind === "party" && partyChoice !== undefined) {
+    // BattleMonMenu. STATS opens the stats screen, which is not ported.
+    const slot = partyChoice;
+    buttons.push(
+      button("SWITCH", () => {
+        partyChoice = undefined;
+        runtime.battleChoose(slot);
+      }),
+      button("STATS", () => {}, {
+        disabled: "The stats screen is not ported yet.",
+      }),
+      button("CANCEL", () => {
+        partyChoice = undefined;
+        showWorld(world);
+      }),
+    );
+  } else if (prompt?.kind === "party") {
+    party.forEach((mon, slot) =>
+      buttons.push(
+        button(
+          mon.nickname,
+          () => {
+            if (!prompt.menu) return runtime.battleChoose(slot);
+            partyChoice = slot;
+            showWorld(world);
+          },
+          {
+            detail: `:L${mon.level} HP ${mon.hp}/${mon.stats[0]}${
+              mon.status ? ` ${statusName(mon.status)}` : ""
+            }`,
+            wide: true,
+          },
+        ),
+      ),
+    );
+    if (prompt.cancel)
+      buttons.push(
+        button("CANCEL", () => runtime.battleChoose(-1), { wide: true }),
+      );
   } else if (prompt?.kind === "forget") {
     prompt.moves.forEach((move, index) =>
       buttons.push(