Based on the repository's commit message style and the changes in the diff, here's an appropriate commit message:

```
feat: add websocket tests, PoA metrics, marketplace endpoints, and enhanced observability

- Add comprehensive websocket tests for blocks and transactions streams including multi-subscriber and high-volume scenarios
- Extend PoA consensus with per-proposer block metrics and rotation tracking
- Add latest block interval gauge and RPC error spike alerting
- Enhance mock coordinator

apps/marketplace-web/src/lib/auth.ts

@@ -0,0 +1,33 @@
+export interface MarketplaceSession {
+  token: string;
+  expiresAt: number;
+}
+
+const STORAGE_KEY = "marketplace-session";
+
+export function saveSession(session: MarketplaceSession): void {
+  localStorage.setItem(STORAGE_KEY, JSON.stringify(session));
+}
+
+export function loadSession(): MarketplaceSession | null {
+  const raw = localStorage.getItem(STORAGE_KEY);
+  if (!raw) {
+    return null;
+  }
+  try {
+    const data = JSON.parse(raw) as MarketplaceSession;
+    if (typeof data.token === "string" && typeof data.expiresAt === "number") {
+      if (data.expiresAt > Date.now()) {
+        return data;
+      }
+      clearSession();
+    }
+  } catch (error) {
+    console.warn("Failed to parse stored marketplace session", error);
+  }
+  return null;
+}
+
+export function clearSession(): void {
+  localStorage.removeItem(STORAGE_KEY);
+}