feat: expand sudoku analysis and interoperability

tests/state/gridNavigation.test.ts

@@ -0,0 +1,27 @@
+import { describe, expect, it } from "vitest";
+import { navigateGridCell } from "../../src/state/gridNavigation";
+
+describe("accessible grid navigation", () => {
+  it("moves with arrows without wrapping at edges", () => {
+    expect(navigateGridCell(4, 3, "ArrowRight")).toBe(5);
+    expect(navigateGridCell(5, 3, "ArrowRight")).toBe(5);
+    expect(navigateGridCell(3, 3, "ArrowLeft")).toBe(3);
+    expect(navigateGridCell(1, 3, "ArrowUp")).toBe(1);
+    expect(navigateGridCell(7, 3, "ArrowDown")).toBe(7);
+  });
+
+  it("supports row, grid and column-edge shortcuts", () => {
+    expect(navigateGridCell(4, 3, "Home")).toBe(3);
+    expect(navigateGridCell(4, 3, "End")).toBe(5);
+    expect(navigateGridCell(4, 3, "Home", true)).toBe(0);
+    expect(navigateGridCell(4, 3, "End", true)).toBe(8);
+    expect(navigateGridCell(4, 3, "PageUp")).toBe(1);
+    expect(navigateGridCell(4, 3, "PageDown")).toBe(7);
+  });
+
+  it("ignores non-navigation keys and rejects unsafe inputs", () => {
+    expect(navigateGridCell(0, 9, "Enter")).toBeNull();
+    expect(() => navigateGridCell(-1, 9, "Home")).toThrow(/outside/i);
+    expect(() => navigateGridCell(0, 0, "Home")).toThrow(/size/i);
+  });
+});