feat(fuzz): add input robustness testing harnesses and fixes

- Add fuzz testing scripts for `nostrEventSchemas.js`, `dmDecryptor.js`, and `magnetUtils.js` in `scripts/agent/`.
- Fix `build...` functions in `nostrEventSchemas.js` to handle `null`/`undefined` inputs.
- Fix `buildVideoPostEvent` to gracefully handle circular references in content serialization.
- Fix `normalizeAndAugmentMagnet` in `magnetUtils.js` to handle non-iterable `extraTrackers`.
- Include minimal reproducers for discovered crashes in `examples/reproducers/`.

scripts/agent/fuzz-utils.mjs

@@ -0,0 +1,94 @@
+
+import { randomBytes } from 'crypto';
+
+export function randomString(length = 100) {
+    const chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!@#$%^&*()_+-=[]{}|;:,.<>?/`~';
+    let result = '';
+    for (let i = 0; i < length; i++) {
+        result += chars.charAt(Math.floor(Math.random() * chars.length));
+    }
+    return result;
+}
+
+export function randomUnicodeString(length = 100) {
+    let result = '';
+    for (let i = 0; i < length; i++) {
+        // Random printable unicode range (roughly)
+        result += String.fromCharCode(Math.floor(Math.random() * 0xFFFF));
+    }
+    return result;
+}
+
+export function randomSurrogateString(length = 100) {
+  let result = '';
+  for (let i = 0; i < length; i++) {
+    // Generate random surrogates
+    const code = Math.random() > 0.5
+      ? Math.floor(0xD800 + Math.random() * (0xDBFF - 0xD800 + 1))
+      : Math.floor(0xDC00 + Math.random() * (0xDFFF - 0xDC00 + 1));
+    result += String.fromCharCode(code);
+  }
+  return result;
+}
+
+export function randomInt(max = 10000) {
+    return Math.floor(Math.random() * max);
+}
+
+export function randomBool() {
+    return Math.random() > 0.5;
+}
+
+export function randomObject(depth = 2) {
+    if (depth <= 0) return randomString(10);
+    const obj = {};
+    const keys = randomInt(5) + 1;
+    for (let i = 0; i < keys; i++) {
+        obj[randomString(5)] = Math.random() > 0.5 ? randomString(10) : randomObject(depth - 1);
+    }
+    return obj;
+}
+
+export function randomHex(length = 64) {
+    return randomBytes(length / 2).toString('hex');
+}
+
+export function pickRandom(arr) {
+    return arr[Math.floor(Math.random() * arr.length)];
+}
+
+export function fuzzGenerators() {
+    const generators = [
+        () => null,
+        () => undefined,
+        () => "",
+        () => "   ",
+        () => 0,
+        () => 1,
+        () => -1,
+        () => NaN,
+        () => Infinity,
+        () => -Infinity,
+        () => [],
+        () => [null],
+        () => {},
+        () => randomString(1000),
+        () => randomUnicodeString(100),
+        () => randomSurrogateString(20),
+        () => randomObject(),
+        () => randomHex(64),
+        () => "magnet:?xt=urn:btih:" + randomHex(40),
+        () => "https://" + randomString(20) + ".com",
+        () => {
+            const obj = {};
+            obj.self = obj;
+            return obj; // Circular
+        }
+    ];
+    return generators;
+}
+
+export function getRandomFuzzInput() {
+    const gens = fuzzGenerators();
+    return pickRandom(gens)();
+}