fix(slashing-protection): more robust solution to determine min epoch

Epochs array might have more than ~10^5 elements, cannot use `Math.min`
as it would throw `RangeError: Maximum call stack size exceeded`.

packages/validator/src/slashingProtection/utils.ts

@@ -28,7 +28,7 @@ export function numToString(num: number): string {
 }
 
 export function minEpoch(epochs: Epoch[]): Epoch | null {
-  return epochs.length > 0 ? Math.min(...epochs) : null;
+  return epochs.length > 0 ? epochs.reduce((minEpoch, epoch) => (minEpoch < epoch ? minEpoch : epoch)) : null;
 }
 
 export function uniqueVectorArr(buffers: Uint8Array[]): Uint8Array[] {

packages/validator/test/unit/slashingProtection/utils.test.ts

@@ -0,0 +1,28 @@
+import {expect} from "chai";
+import {Epoch} from "@lodestar/types";
+import {minEpoch} from "../../../src/slashingProtection/utils.js";
+
+describe("slashingProtection / utils / minEpoch", () => {
+  it("should return the minimum epoch from an array of epochs", () => {
+    const epochs: Epoch[] = [15, 10, 20, 30, 5, 1, 50];
+    const result = minEpoch(epochs);
+    expect(result).to.equal(1);
+  });
+
+  it("should return the only epoch if epochs array only contains one element", () => {
+    const epochs: Epoch[] = [10];
+    const result = minEpoch(epochs);
+    expect(result).to.equal(10);
+  });
+
+  it("should return null if epochs array is empty", () => {
+    const epochs: Epoch[] = [];
+    const result = minEpoch(epochs);
+    expect(result).to.equal(null);
+  });
+
+  it("should not throw 'RangeError: Maximum call stack size exceeded' for huge epoch arrays", () => {
+    const epochs = Array.from({length: 1e6}, (_, index) => index);
+    expect(() => minEpoch(epochs)).to.not.throw(RangeError);
+  });
+});