Add implementation

src/lib/peer.ts

@@ -0,0 +1,22 @@
+const PEER_ID_KEY = "p2p-poll-peer-id";
+
+/** Generate a UUID v4 */
+function generateUUID(): string {
+  return crypto.randomUUID();
+}
+
+/**
+ * Get or create a persistent peer ID.
+ * Stored in localStorage so each browser tab/device gets a stable identity.
+ */
+export function getPeerId(): string {
+  if (typeof globalThis.localStorage === "undefined") {
+    return generateUUID();
+  }
+  let id = localStorage.getItem(PEER_ID_KEY);
+  if (!id) {
+    id = generateUUID();
+    localStorage.setItem(PEER_ID_KEY, id);
+  }
+  return id;
+}