feat: Rollback steps back through the last 50 interactions (wheel up, PageUp, Rollback action)

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

frontend/src/player/engine.ts

@@ -48,6 +48,9 @@ function fontGroup() {
   return group;
 }
 
+/** How many interactions Rollback can step back through. */
+const ROLLBACK_LIMIT = 50;
+
 export class Engine {
   private liveImages?: LiveImages;
   private imageScales = new Map<string, number>();
@@ -83,6 +86,8 @@ export class Engine {
   private windowShown = true;
   private lastSay: { name: string; text: string; color?: string; char?: CharacterDef } | null = null;
   private history: { name: string; text: string }[] = [];
+  /** One state per interaction, newest last: what Rollback steps back through. */
+  private rollbackLog: { snap: SaveData; history: { name: string; text: string }[] }[] = [];
   private nvlLines: HTMLElement[] = [];
   private interactions = 0;
 
@@ -1061,6 +1066,7 @@ export class Engine {
       quit: () => this.onExit(),
       mainMenu: () => this.restart(() => { this.stack = []; this.cur = { label: "", path: [0] }; }),
       openMenu: () => this.openGameMenu(),
+      rollback: () => this.rollback(),
       openUrl: (url) => {
         if (/^https?:\/\//i.test(url)) window.open(url, "_blank", "noopener,noreferrer");
       },
@@ -1531,11 +1537,24 @@ export class Engine {
 
   private interactionStart() {
     this.renderer.commit();
+    this.rollbackLog.push({ snap: this.snapshotState(), history: this.history.slice() });
+    if (this.rollbackLog.length > ROLLBACK_LIMIT) this.rollbackLog.shift();
     this.interactions++;
     if (this.interactions % 15 === 0) void this.save("auto", true);
     this.preloadAhead();
   }
 
+  /** Back to the previous interaction: the one being shown is dropped, the one before it is shown again. */
+  private rollback() {
+    if (!this.running || this.rollbackLog.length < 2) return;
+    this.rollbackLog.pop();
+    const entry = this.rollbackLog.pop()!;
+    this.restart(() => {
+      this.applySave(entry.snap);
+      this.history = entry.history;
+    });
+  }
+
   private preloadAhead() {
     const block = this.labels.has(this.cur.label) ? this.blockFor(this.cur) : [];
     const start = this.cur.path[this.cur.path.length - 1];
@@ -1878,6 +1897,7 @@ export class Engine {
       this.newStore();
       this.stack = [];
       this.history = [];
+      this.rollbackLog = [];
       this.lastSay = null;
       this.textbox.classList.add("pg-hidden");
       this.cur = at ?? { label: this.game.entry, path: [0] };
@@ -1973,6 +1993,7 @@ export class Engine {
     }
     if (!data.revision && !(await this.confirmAsk("Старое сохранение не содержит ревизию игры. После изменения скрипта его позиции могут быть неверны. Попробовать загрузить?", "Загрузить"))) return;
     this.replayStash = null;
+    this.rollbackLog = [];
     this.restart(() => this.applySave(data));
   }
 
@@ -2123,7 +2144,7 @@ export class Engine {
       this.advanceInput();
     });
     stage.addEventListener("wheel", (ev) => {
-      if (ev.deltaY < 0 && this.screen.classList.contains("pg-hidden") && this.running) this.openHistory();
+      if (ev.deltaY < 0 && this.screen.classList.contains("pg-hidden") && this.running) this.rollback();
     }, { passive: true });
   }
 
@@ -2203,6 +2224,9 @@ export class Engine {
       this.setSkip(!this.skip);
     } else if (ev.key === "a" || ev.key === "ф") {
       this.setAuto(!this.auto);
+    } else if (ev.key === "PageUp") {
+      ev.preventDefault();
+      this.rollback();
     } else if (ev.key === "h" || ev.key === "р") {
       this.textbox.classList.toggle("pg-ui-hidden");
     }

frontend/src/player/screens.ts

@@ -43,6 +43,8 @@ export interface ScreenHost {
   quit(): void;
   mainMenu(): void;
   openMenu(): void;
+  /** The Rollback action: back to the previous interaction. */
+  rollback?(): void;
   openUrl(url: string): void;
   quickSave(): void;
   quickLoad(): void;
@@ -1797,7 +1799,7 @@ export class ScreenManager {
       case "UploadSync":
       case "DownloadSync": this.host.notify("Синхронизация недоступна в браузере"); return;
       case "Skip": this.host.setSkipping?.(true); return;
-      case "Rollback": return;  // there is no rollback in the browser player
+      case "Rollback": this.host.rollback?.(); return;
       case "ToggleLocalVariable": {
         const now = owner?.vars.get(a);
         owner?.vars.set(a, !truthy(now));