feat: complete advanced Sudoku workbench

tests/state/playHistoryPersistence.test.ts

@@ -0,0 +1,36 @@
+import { describe, expect, it } from "vitest";
+import {
+  createGameplayHistory,
+  parseGameplayHistory,
+  serializeGameplayHistory,
+} from "../../src/state/playHistory";
+import { createSession } from "../../src/state/session";
+
+describe("gameplay history persistence", () => {
+  it("round-trips independent bounded history", () => {
+    const history = createGameplayHistory(
+      createSession(Array<number>(16).fill(0)),
+    );
+    const encoded = serializeGameplayHistory(history, 4);
+    const decoded = parseGameplayHistory(encoded, 4);
+    expect(decoded).toEqual(history);
+    (decoded.moments[0]!.state.values as number[])[0] = 4;
+    expect(history.moments[0]!.state.values[0]).toBe(0);
+  });
+
+  it("rejects dangling and oversized persisted state", () => {
+    const history = createGameplayHistory(
+      createSession(Array<number>(16).fill(0)),
+    );
+    const raw = JSON.parse(serializeGameplayHistory(history, 4)) as {
+      history: { currentMomentId: string };
+    };
+    raw.history.currentMomentId = "missing";
+    expect(() => parseGameplayHistory(JSON.stringify(raw), 4)).toThrow(
+      /missing active branch or moment/u,
+    );
+    expect(() => parseGameplayHistory("x".repeat(1_048_577), 4)).toThrow(
+      /too large/u,
+    );
+  });
+});